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PROPLAB-PRO
Version 2.0
High Frequency Radio Propagation Laboratory
© Copyright 1994-1996 by the
Solar Terrestrial Dispatch
USER'S MANUAL
TABLE OF CONTENTS
SECTION 1 - INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Introduction to PROPLAB PRO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SECTION 2 - BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 The Ionosphere and magnetosphere . . . . . . . . . . . . . . .
2.2 Solar-Terrestrial Relationships . . . . . . . . . . . . . . . . . .
2.2.1 General Features of the Sun . . . . . . . . . . . . . .
2.2.2 Solar Activity and Solar Cycles . . . . . . . . . . .
2.2.3 Flare Rating System . . . . . . . . . . . . . . . . . . . .
2.3 Geomagnetic Indices . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.1 The Geomagnetic K-Index . . . . . . . . . . . . . . .
2.3.2 The Geomagnetic A-Index . . . . . . . . . . . . . . .
2.4 The Auroral Zones . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.1 Importance to HF Propagation . . . . . . . . . . . .
2.4.2 Auroral Phenomena . . . . . . . . . . . . . . . . . . . .
2.5 Polar Cap Absorption (PCA) . . . . . . . . . . . . . . . . . . . .
2.6 Ionospheric Radio Propagation . . . . . . . . . . . . . . . . . .
2.6.1 Ionospheric Reflection and Refraction . . . . . .
2.6.2 Ionospheric Critical Frequencies and Heights .
2.6.3 The International Reference Ionosphere . . . . .
2.6.4 Propagation Paths . . . . . . . . . . . . . . . . . . . . .
2.6.5 Determining Propagation Conditions . . . . . . .
2.6.6 Skip Distance and Maximum Usable Frequency
2.7 Ray Tracing Techniques . . . . . . . . . . . . . . . . . . . . . . .
SECTION
3.1
3.2
3.3
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3 - PROPLAB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation of PROPLAB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Running PROPLAB, Changing Colors, and Setting Up the Printer
Setting the Required Parameters . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.1 Setting the Transmitter/Receiver Locations and Time Zones
3.3.2 Graphically Setup Transmitter/Receiver Locations . . . . . .
3.3.3 Ray Tracing Speed, Path Type, and Termination Mode . .
3.3.4 Choosing Ionospheric Models (URSI or CCIR) . . . . . . . . .
3.3.4.1 Models to use with the Simple Ray-Tracing
Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.2 Models to use with the Complex Ray-Tracing
Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.3 The "Right" Model to Use . . . . . . . . . . . . . . . . .
3.3.5 Setting the Operating Frequency . . . . . . . . . . . . . . . . . . .
3.3.6 Setting the Date/Time and Auto-Sunspot-Number
Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.3.7 Setting the Transmitter Power . . . . . . . . . . . . . . . . . . . . . . .
3.3.8 Setting Ranges and Steps . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.9 Selecting Local or Universal Time . . . . . . . . . . . . . . . . . . . .
3.3.10 Setting the Geomagnetic A-Index . . . . . . . . . . . . . . . . . . . .
3.3.11 Setting the Sunspot Number or Solar Flux . . . . . . . . . . . . .
3.3.12 Selecting the Number of Allowed Hops . . . . . . . . . . . . . . . .
3.3.13 Selecting PROPLAB's Quick or Normal Modes . . . . . . . . . .
3.3.14 Selecting Plane or Spherical Grids . . . . . . . . . . . . . . . . . . .
3.3.15 Selecting Grid Distances and Height Scales . . . . . . . . . . . . .
3.3.16 Accounting for Solar Flares . . . . . . . . . . . . . . . . . . . . . . . .
3.3.17 Defining Polar Cap Absorption and Screen Saving Functions
3.3.18 Other Comprehensive Ray-Tracing Options . . . . . . . . . . . .
3.3.18.1 Ray-Tracing Model / Ray Type . . . . . . . . . . . . . . .
3.3.18.2 Magnetic Field Model . . . . . . . . . . . . . . . . . . . . . .
3.3.18.3 Collision Frequency Model . . . . . . . . . . . . . . . . . .
3.3.18.4 Electron Density Model . . . . . . . . . . . . . . . . . . . . .
3.3.18.5 Integration Method . . . . . . . . . . . . . . . . . . . . . . . .
3.3.18.6 Display Method . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.18.7 Transmitter / Receiver Height . . . . . . . . . . . . . . . .
3.3.18.8 Ray-Tracing Rate / Steps per hop . . . . . . . . . . . . .
3.3.18.9 Magnetic Pole Lat / Lon . . . . . . . . . . . . . . . . . . . .
3.3.18.10 Maximum / Minimum Ray-Tracing Step Length .
3.3.18.11 Left Latitude / Longitude of Display . . . . . . . . . .
3.3.18.12 Right Latitude / Longitude of Display . . . . . . . . .
3.3.18.13 Grid Distance and Ticks . . . . . . . . . . . . . . . . . . .
3.3.18.14 Distance between Ticks in Altitude . . . . . . . . . . . .
3.3.18.15 3-D Rotation Angles for the X / Y / and Z Axes . .
3.3.18.16 Zoom Factors and X / Y Axis Offsets . . . . . . . . . .
3.3.18.17 HMax (and Altitude Grid) / Ym / and foF2 Layer
Shaping Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.18.18 Ground Gyrofrequency at the Equator . . . . . . . . .
3.3.18.19 Electron Collision Frequency and Profile Shaping
Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.18.20 Three-Dimensional Data (Important!) . . . . . . . . .
3.4 PROPLAB's Main Menu Functions . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1 Ray Tracing Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1.1 Ray Tracing Signals using the Simple Ray-Tracing
Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1.2 Ray Tracing Signals using the Comprehensive RayTracing Technique . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1.3 Understanding the Generation of Ionospheric Profiles
3.4.1.4 Understanding the Three-Dimensional Grid . . . . . . .
3.4.1.5 The Text File Ray-Tracing Results . . . . . . . . . . . . .
3.4.2 Computing MUFs between any two points . . . . . . . . . . . . . .
3.4.3 Setting up Regions of Sporadic-E . . . . . . . . . . . . . . . . . . . . .
3.4.4 Setting up Transmitter and Receiver Locations . . . . . . . . . . .
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3.4.5 Plotting Electron Density Profiles . . . . . . . . . . . . . . . . . . . . . . .
3.4.6 Displaying Ionospheric Profile Statistics . . . . . . . . . . . . . . . . . .
3.4.7 Quitting PROPLAB and returning to DOS . . . . . . . . . . . . . . . .
SECTION 4 - GLOBAL IONOSPHERIC MAPS . . . . . . . . . . .
4.1 Global Maps of Critical F2-Layer Frequencies . . . . .
4.2 Global Maps of Ionospheric M-Factors . . . . . . . . . .
4.3 Global Maps of Maximum Usable Frequencies . . . .
4.4 Global Maps of the Height Maximum of the F2-Layer
4.5 Generating Maps of Critical E-Layer Frequencies . .
4.6 Producing Maps of Solar Zenith Angles . . . . . . . . .
4.7 Producing Maps of Magnetic DIP Angles . . . . . . . .
4.8 Global Maps of Magnetic Field Total Intensity . . . .
4.9 Global Maps of Magnetic Latitude . . . . . . . . . . . . .
4.10 Producing Maps of Modified DIP Angles . . . . . . . .
4.11 Transverse Plasma Frequency Maps . . . . . . . . . . .
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SECTION 5 - SIMPLE RAY TRACING SCREEN . . . . . . . . . . . .
5.1 Location, Azimuth, Distance of the Transmitter/Receiver
5.2 UTC Time and Operational Frequency . . . . . . . . . . . .
5.3 CUR Lat and CUR Lon Statistics . . . . . . . . . . . . . . . .
5.4 Signal Air Distance Statistic . . . . . . . . . . . . . . . . . . . .
5.5 CURrent Angle of the Signal . . . . . . . . . . . . . . . . . . . .
5.6 The Electron Density Graph and Numeric Density . . . .
5.7 Estimated Signal Strength Bar Graph . . . . . . . . . . . . .
5.8 Signal Quality Bar Graph . . . . . . . . . . . . . . . . . . . . . .
5.9 Magnetic Coordinates of the Ray . . . . . . . . . . . . . . . .
5.10 Solar Elevation Angle at the Ray Location . . . . . . . . .
5.11 Height or Altitude of the Ray . . . . . . . . . . . . . . . . . .
5.12 Plasma Frequency at the Ray Height . . . . . . . . . . . . .
5.13 Signal Elevation Angle . . . . . . . . . . . . . . . . . . . . . . .
5.14 Auroral Zone Statistics . . . . . . . . . . . . . . . . . . . . . . .
5.15 Ionospheric Distance Travelled . . . . . . . . . . . . . . . . .
5.16 Identifying the Receiver Location . . . . . . . . . . . . . . .
5.17 Pausing and Skipping Traced Rays . . . . . . . . . . . . . .
5.18 Aborting Ray Tracing and Saving Screen Images . . . .
5.19 Identifying Regions of Sporadic-E . . . . . . . . . . . . . . .
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SECTION
6.1
6.2
6.3
6.4
6.5
6.6
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6 - SIMPLE AREA COVERAGE MAPS . . . . . .
How are Broadcast Coverage Maps Constructed?
Beginning Inputs . . . . . . . . . . . . . . . . . . . . . . . .
Computing the Required Data . . . . . . . . . . . . . .
Types of Broadcast Coverage Maps Available . .
Required Map-Generation Inputs . . . . . . . . . . .
Available Commands while Viewing Maps . . . . .
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SECTION 7 - COMBINING MAPS
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SECTION
8.1
8.2
8.3
8 - ALL-BAND SPECTRUM ANALYSIS . . . . . . . .
What is an Oblique Sounding Ionogram? . . . . . . .
Phase 1: Collecting the Required Data . . . . . . . . . .
Phase 2: Analyzing the Results . . . . . . . . . . . . . . .
8.3.1 The Propagation-Delay Plot . . . . . . . . . . .
8.3.2 Elevation Angle Plots . . . . . . . . . . . . . . . .
8.4 Applying the Results . . . . . . . . . . . . . . . . . . . . . . .
8.5 Commands Available While Viewing Ionogram Plots
SECTION
9.1
9.2
9.3
9.4
9.5
9.6
9.7
9 - COMPLEX AREA-COVERAGE MAPS . . . .
Types of Broadcast Coverage Maps Supported .
Type of Rays to Include . . . . . . . . . . . . . . . . . .
Specifying the Window Corner Coordinates of the
Specifying Limits for Collected Data . . . . . . . . .
Other Map and Contouring Options . . . . . . . . .
Database Offset Value . . . . . . . . . . . . . . . . . . . .
The Plotted Map . . . . . . . . . . . . . . . . . . . . . . . .
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SECTION 10 - ANTENNAS . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1 Selecting Existing Antennas . . . . . . . . . . . . . . . . .
10.2 Displaying the Radiation Pattern . . . . . . . . . . . . .
10.3 Creating Your Own Antenna Radiation Patterns or
Modifying/Deleting Existing Patterns . . . . . . . . .
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SECTION 11 - REAL-TIME MAPS . . . . . . . . . . . . . . . . . . . . .
11.1 Setting the Gray Angle . . . . . . . . . . . . . . . . . . . . .
11.2 Real-Time Global Ionospheric Maps . . . . . . . . . . .
11.3 Update Rates for the Real-Time Maps . . . . . . . . . .
11.4 Displaying Local Times for Cities Around the World
11.5 Commands Available While Viewing Maps . . . . . .
SECTION 12 - HOURLY MUF GRAPHS
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120
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
1
SECTION 1 - INTRODUCTION
1.1 Introduction to PROPLAB PRO
For years, the ionosphere has been used as a major avenue of communication. The
unique ability of the ionosphere to bend and reflect radio waves has been a topi c of heavy
study for decades. Over the many years since we began studying the ionosphere, w e have
learned a great deal about the characteristics and true nature of the ionosphere . Many books
have been devoted to this subject 1.
Over the last 20 years, computers have been used with ever increasing frequency to
study the effects of radio signal refraction - or the bending of radio waves - w ithin the
ionosphere. In the last 10 years, personal computers have become significantly m ore
powerful and capable of performing the complex functions necessary to analyze th e
ionosphere in relative detail. It is then no wonder that we have made many of th e major
strides in the field of ionospheric radio propagation in this same period of tim e.
There are many computer programs presently available for predicting such quantit ies
as the Maximum Usable Frequency (or MUF), great-circle paths (or the path travel led by a
radio signal from one location to another), and graylines (or the regions where the Sun is
either rising or setting). Several of these have advanced features such as the a bility to
compute signal strengths between two points, or optimum times of transmission.
PROPLAB PRO contains all of these features and many others which have previously
only been found on the larger main-frame computers available to researchers and scientists.
For example, PROPLAB PRO is the only propagation software in the world for IBM or
compatible personal computers that will show you the precise behavior of radio s ignals as
they travel through the ionosphere. It effectively simulates radio transmissions into the
ionosphere with a high-degree of accuracy by using sophisticated ionospheric ray -tracing
techniques.
It is hoped this manual will help teach the reader how to use and interpret the
numerous available features of PROPLAB as well as how to better understand the i onosphere.
This manual may therefore serve as both a tutor and a reference. Most, if not al l, of
the illustrations given in this manual, were generated by the PROPLAB PRO softwa re.
1
.
,
(1990)
.,
, . .
(1985),
2
SECTION 2 - BACKGROUND
2.1 The Ionosphere and magnetosphere
The ionosphere is that region of our upper atmosphere which lies between about 5 0
km and several Earth radii. For our purposes, the ionosphere is defined as the r egion between
about 50 km and 1000 km. This is the area where the major effects of signal refr action take
place. It also encompasses almost all of the phenomena which can affect radio
communications. Figure 2.0 below illustrates the structure of the ionosphere on a quiet
summer day.
Figure 2.0: Typical Electron Density Profile for a Summer Day
The peak electron density
of the ionosphere usually occurs
in the F region of the ionosphere.
The F-region is divided into two
regions known as F1 and F2.
The F1 region is the lower of the
two. Both of these regions are
ionized with extreme ultraviolet
light (EUV). The F1 layer is not
always present in the ionosphere.
Often, the F2 layer is large
enough to encompass the F1
layer. In Figure 2.0, the exact
location of the F1 region is
difficult to discern due to the
density and spatial extent of
ionization in the F2 layer.
The E-region of the ionosphere lies between approximately 90 and 140 km and is a
fairly dynamic region of the ionosphere. Sporadic-E, or areas of localized and s poradically
intense ionization, occurs between about 100 and 115 km with a peak near 105 km. The Eregion is ionized by soft x-ray solar radiation.
The D-region lies between about 50 and 90 km and contains the D-layer as well as
another less-influential layer known as the C-layer, or Cosmic Ray layer. The la tter is ionized
by high-energy cosmic rays which are occasionally observed following strong sola r proton
flares. The D-layer is ionized with hard x-rays or Lyman Alpha radiation.
Above the peak of the electron density, which usually occurs in the F2 layer, th e
electron density decreases relatively slowly (exponentially) with altitude. This region is
known as the Topside of the ionosphere. Above the topside lies the protonosphere and the
plasmasphere, which are not well defined boundaries and stretch for many thousan ds of
3
kilometers in height.
The ionosphere is strongly dependent on the condition of the geomagnetic field. The
geomagnetic field cocoons the Earth and stretches out on the dark-side of the Ea rth for
millions of kilometers. If we could see the magnetic field of the Earth from a d istance, it
would resemble a comet, with the Earth as the "head".
The solar wind is a stream of charged particles emanating from the Sun. This "wi nd"
blows at speeds of between 250 and 350 kilometers (km) per second under relative ly quiet
conditions. The magnetic field of the Sun is usually pulled out along with the s olar wind.
When the solar wind reaches the Earth, the magnetosphere of the Earth is pulled out along
with the solar wind. It is this which forms the "cometary" appearance of our mag netic field.
When the solar wind reaches the magnetosphere of our Earth, our magnetosphere
deflects much of the solar wind stream around the Earth. The flow of this solar wind over
our magnetic field generates a great deal of energy which is (to some extent) st ored by the
magnetic field of the Earth. Occasionally, this energy is suddenly released. The resulting
disturbance is known as a geomagnetic substorm. A geomagnetic storm is made up o f many
substorms and can have a serious impact on the ionosphere.
Geomagnetic storms are almost always associated with decreases in electron densi ty in
the F-region, which results in a lowering of the maximum usable frequency. This decreases
the usable bandwidth and can cause difficulties in communicating over long dista nces. We
will discuss this in greater detail later.
2.2 Solar-Terrestrial Relationships
The Sun is an integral part of our environment. We depend on it for life-sustain ing
light, energy, and heat. It is essential that we have a basic understanding of h ow the Sun can
influence the ionosphere before we can expect to understand the behaviour and ch aracter of
the ionosphere. This section is devoted to explaining how the sun interacts with our
terrestrial environment, and particularly the ionospheric environment.
2.2.1 General Features of the Sun
The Sun lies at an average distance of 149,600,000 kilometers (or 93,500,000 mil es)
from the Earth. The Sun is about 330,000 times more massive than the Earth and t he Moon
combined. It has a photospheric temperature of about 5800 degrees Kelvin and a
gravitational pull over 333,000 times stronger than here on Earth. The average r adius of the
Sun is 109 times larger than the radius of the Earth, or about 696,000 km. It ta kes
approximately 27 days for the solar equatorial regions to complete one rotation. We could fit
over 1.3 million Earths inside of the Sun.
4
The Sun is composed of an interior region which lies below the visible photosphe re.
Above the photosphere lies the chromosphere or lower solar atmosphere. The coron a forms
the outer atmosphere of the Sun. About 99.9 percent of the Sun is composed of hy drogen
and helium, and of these elements, hydrogen is by far the most abundant (92.1%). The
photosphere of the Sun represents that region of the solar atmosphere where the gaseous
density increases rapidly to the point where features below the boundary of the photosphere
appear opaque.
The temperature above the photosphere falls to a value of about 4200 K approxima tely
5000 km in altitude. Thereafter, the temperature increases to approximately 1 to 3 million
degrees Kelvin in the coronal regions.
2.2.2 Solar Activity and Solar Cycles
With the naked (protected) eye, the Sun appears as an almost featureless disk.
However, using telescopes, it has been determined that this is not true. The Sun contains
many different types of phenomena. Perhaps most significant are the appearance o f Sunspots.
Sunspots were first discovered by Theophrastus near 325 BC. These dark spots for m and
disappear over time intervals ranging from less than a day to several months. Su nspots
appear dark because the temperature (about 3000 K) within the dark regions is lo wer than that
of the surrounding hotter (and therefore brighter) gas. If a sunspot were remove d from the
Sun and placed in orbit some distance away from the Sun, it would appear as a ve ry luminous
object.
All sunspots (and other features) rotate from east to west. Both the Sun and the Earth
rotate in the same direction, and the Earth orbits around the Sun in the same di rection as the
Sun rotates. The Earth is a solid body and rotates from east to west at the same rate over all
of the Earth. The Sun, however, is a gaseous body and rotates faster at the sola r equator than
at the poles. This differential rotation helps to explain some of the processes occurring on
(and inside) the Sun.
One of the most notable features of the Sun is the 11-year cycle of activity tha t it
undergoes. For several hundred years (since about the year 1600), astronomers ha ve been
recording the number of sunspots that have been visible on the surface of the Su n.
Approximately every 11 years, sunspots increase in number and complexity on the Sun. This
11-year cycle is presently used to help forecast the magnitude of future solar c ycles.
Sunspots are associated with strong solar magnetic fields. A strong field within a
sunspot may approach 0.4 tesla, or about 4000 gammas. This is approximately 6 to 7 percent
of the total strength of our Earth's magnetic field. During the maximum of the 1 1-year
sunspot cycle, the total combined magnetic field strength of all visible spots m ay exceed the
entire strength of our Earth's magnetic field by many times. Sunspot groups are often
associated with many individual fields which may intertwine and interact with on e another.
5
Just as a bar magnet has both a north and a south pole, sunspots are also polari zed
with either positive or negative polarity. Most often, sunspots appear as bipola r groups, or
regions where both positive and negative polarities exist. When conditions are r ight, these
opposite polarity magnetic fields can interact and react with one another to pro duce sudden
releases of energy known as solar flares. These explosions of magnetic energy ca n be
observed using special filters on optical telescopes known as Hydrogen-Alpha fil ters. These
filters permit the observation of the solar chromosphere where solar flares orig inate.
The processes involved in the production of solar flares is not yet well known.
Currently, it is believed that flares are related to coronal mass ejections (or CMEs). CMEs
are events on the sun where mass is ejected from the Sun. Coronal mass ejections may
interfere with the magnetic fields within sunspot regions and trigger solar flar es. It is
presently believed that this may be a dominating role in flare production. Previ ously, it was
believed flares themselves may have been responsible for producing the CMEs. How ever, it
now appears the opposite may be true: CMEs may occur before the flare is observe d,
indicating that the CME is responsible for triggering the flare.
A major type of CME which is often observed are known as disappearing filaments
(or DSFs). Strings of material are often observed "floating" above the surface o f the Sun.
These ropes of gas are suspended above the surface of the Sun by magnetic fields . This
process results in the cooling of the gas, which makes it appear darker than the brighter (and
hotter) photospheric surface. When observed on the limb, the suspension of the g as above the
surface of the Sun can be clearly discerned, and the gas is luminous against the darker
background of space. Occasionally, one (or some) of the magnetic fields suspendi ng the gas
above the solar surface may break free from the surface. This may cause the gas to begin
erupting upward and outward from the Sun. This is known as an erupting filament. Some
very impressive erupting filaments have been observed as limb events on the Sun. When
observed against the brighter photospheric surface, the dark string of material within the
erupting filament simply disappears. From this follows the term, "disappearing f ilament."
Filaments (and other coronal mass ejections related to the more energetic solar flaring
processes), are capable of spewing out mass from the Sun that may quickly travel the large
distance from the Sun to the Earth. These disturbances are often travelling at s peeds
significantly greater than the background speed of the solar wind. When this occ urs, a
shockwave (not unlike the shockwaves that are formed by supersonic aircraft) may form at
the front of the disturbance. Within 2 or 3 days, this material may arrive at th e Earth and
slam into the Earth's magnetosphere at speeds as high as 7,200,000 kilometers an hour (or
4,500,000 miles per hour, or 2,000 kilometers per second). The magnetosphere res ponds to
this sudden increase in solar wind speed (and pressure) by springing inward or b eing suddenly
compressed. This can be observed in space (and on the ground) by magnetometers w hich are
capable of measuring the strength of the Earth's magnetic field. Compression of our
magnetosphere causes the strength of the magnetic field to increase. This sudden
enhancement in the strength of the magnetic field is known as a sudden impulse ( or SI).
When it is associated with the sudden occurrence of geomagnetic storming, it is known as a
6
sudden storm commencement (or SSC). Strong interplanetary disturbances can make it
difficult for satellite controllers to control their satellites. Uncontrolled tu mbling of satellites
can occur. Satellite surfaces may be electrically charged to levels which may ca use small
discharges within the satellites (and thereby damage some of the electronics).
2.2.3 Flare Rating System
Flares are rated in two different ways. The first method was used earlier this c entury
and is still in wide use today. It involves measuring the brightness of the flar e in the light of
hydrogen-alpha, and measuring the size of the flaring area. This rating system i s composed
of a numerical digit and a letter, corresponding to the measured optical size of the flare and
the brightness of the event, respectively.
Digits are defined as follow and represent the corrected area of the flare in
heliospheric square degrees when the flare is at its maximum brightness in H-Alp ha:
S - Subflare (associated with an area <= 2.0 square degrees).
1 - Importance 1 ( 2.1 <= area <= 5.1 square degrees).
2 - Importance 2 ( 5.2 <= area <= 12.4 square degrees).
3 - Importance 3 (12.5 <= area <= 24.7 square degrees).
4 - Importance 4 (area >= 24.8 square degrees).
The letter which defines the brightness of the flare, at the maximum phase of th e flare,
is defined as follows:
F = Faint.
N = Normal.
B = Brilliant.
All flare locations are given in heliographic longitude, which is a done by meas uring
the distance of the flaring site from the rotational axis of the solar poles, re lative to the limbs
of the Sun. For example, a location of S20E90 refers to a position 20 degrees so uth of the
solar rotational equator and directly on the eastern limb. A location of N40W00 refers to a
position 40 degrees north of the equator and exactly on the central meridian, or the longitude
line which cuts both through the center of the Sun and through the rotational po les (from the
northern pole to the southern pole) as observed from the Earth.
The second rating system is less subjective and depends on the measured brightne ss of
the soft-xray emissions in the wavelength band 1 to 8 Angstroms, as observed by Earthorbiting satellites such as GOES-6 and/or GOES-7 (Geostationary Operational Envi ronmental
Satellites [or GOES]). This system was initiated on 01 January 1969 and ranks so lar activity
by its peak x-ray intensity. This classification method offers two distinct adva ntages
compared with the standard optical classification system: it gives a better meas ure of the
geophysical significance of solar activity, and it provides an objective means o f classifying
geophysically significant activity, regardless of its location on the solar disk or near the solar
7
limb. This rating system is described as follows (all x-ray measurements are in Watts per
square meter):
A
Intensity <
10
-7
B
10
-7
<= Intensity <
10
-6
C
10
-6
<= Intensity <
10
-5
M
10
-5
<= Intensity <
10
-4
X
10
-4
<= Intensity
The letter designates the order of magnitude of the peak x-ray value observed. T he
number following the letter is the multiplicative factor. For example, a M3.2 ev ent indicates
an x-ray burst with a peak flux of 3.2 x 10 -5 Watts per square meter (Wm -2).
The PROPLAB software will accept, as input, the peak magnitude of the x-rays
observed during solar flares to compute circuit quality during flare activity. T he flare rating
system which should be used is this one employed for soft x-rays above. Sources for this
information are given later in this manual.
2.3 Geomagnetic Indices
It is useful to quantify the degree of magnetic disturbance observed each day ov er
various regions of the Earth, or on a global basis. Numerous different types of indices have
been developed and used over the years. 2 Most magnetic observatories determine local
indices. The local indices are then used to compute the global indices. The most popular
indices presently used to measure levels of geomagnetic activity are known as th e A and K
indices. Of these, PROPLAB only uses the A-index, although knowledge of how the A-index
is derived from the K-index is useful.
2.3.1 The Geomagnetic K-Index
The K-index is a value ranging from 0 to 9 and indicates the magnitude of irregu lar
variations occurring with the geomagnetic field over a period of 3 hours, using Universal
Time (UT). For example, one digit is used to define the level of activity occurr ing between
0000 and 0300 UTC. Another digit is used to describe activity levels between 030 0 and 0600
2
.,
,
).
.
, 10,
157.
,
. .,
8
UTC, and so on throughout the UTC day.
Since the level of magnetic disturbance is usually higher in the higher latitude regions,
each observatory is assigned their own rating scale to account for the level of activity
observed at each observatory. For example, an equatorial station may observe sma ll field
variations on the order of several gammas defining a "quiet" interval. On the ot her hand, it
may be normal for a high latitude station to observe field variations on the ord er of several
tens of gammas defining a quiet interval for that region. For this reason, each station is
assigned their own rating scale. However, all stations scale their measurements so that their
K-index values fall within the 0 to 9 range.
The range used, 0 to 9, defines the level of activity observed, from dead-quiet (0), to
extremely disturbed (9). The amplitude range of the magnetic field during a give n 3-hour
interval (that is, the maximum value minus the minimum observed value, in gammas ) is used
to determine the K-index value.
The K-index is quasi-logarithmic and open ended. Each observatory uses a look-up
table created for that specific location, to convert an amplitude range into an associated Kindex value. The table given below shows the look-up table for a typical middle- latitude
magnetic observatory.
K
0
1
2
3
4
5
6
7
8
9
ak
0
3
7
15
27
48
80
140
240
400
The "ak" indices for a particular station may be converted into units of gammas by
multiplying them by a station-specific factor. This factor can be found by divid ing the
stations minimum value for a K-index of 9 (in this case, 400) by 250. So for thi s case, a Kindex of 5 would be associated with an a k index of 27, which would convert to a magnetic
field variation of 27 x 1.6 (400 / 250 = 1.6) = 77 gammas. Another term commonly used
(and coming into greater usage), is the nanotesla (nT). One gamma is equivalent to one
nanotesla.
The planetary K-index values for a given 3-hour interval are obtained by simply
computing the numerical mean of all of the K-indices for all known stations, for each 3-hour
interval.
2.3.2 The Geomagnetic A-Index
This index is based on the K-index as follows. Each K-index for every station is
associated with a given a k index as previously described. The A-index for a particular station
is simply the average of the eight a k-indices for that UTC day. For example, eight K-indices
9
given as "3445 4332" would correspond to an A-index of 23. This is done by compu ting the
average of the associated eight a k indices as follows:
(15 + 27 + 27 + 48 + 27 + 15 + 15 + 7) / 8 = 22.6, or 23.
This simple method of computing the A-indices (and the table given above) can be applied to
most middle latitude regions. High latitude stations will be associated with a d ifferent range
index - ak (one which spans larger ranges).
The PROPLAB software will accept, as input, the A-index value. The A-index value s
broadcast by radio stations WWV and WWVH (on HF frequencies 2.5, 5.0, 10, 15, an d 20
MHz) at 18 minutes past each hour, can be input into the software. Alternatively , for 3-hour
values, the K-index value given in this same message can be converted into an eq uivalent Aindex value (as described above), and then input into the software. This may, un der rapidly
changing circumstances, result in more accurate results.
2.4 The Auroral Zones
The auroral zones can be defined as those areas of the Earth where visible auror a
occurs overhead. They typically occur within an oval-shaped ring centered approx imately on
the north and sound magnetic poles. Two zones of aurorae are therefore visible o n the Earth:
one near the north magnetic pole, and the other near the south magnetic pole. Si nce the
northern magnetic pole lies closest to North America, Canadian regions are well- placed for
observing periods of auroral activity. In the northern hemisphere, this activity is known to the
public as the "northern lights" or the "aurora borealis". In the southern hemisp here, it is
known as the "aurora australis".
The Solar Terrestrial Dispatch has developed a Professional Dynamic Auroral Oval
Simulator for IBM compatible PC computers running MSDOS, which will explicitly d elineate
the location of the auroral ovals for any given hour and level of geomagnetic ac tivity. It will
also show you where in the sky to look for aurorae, and will simulate the intens ity and spatial
extent of activity, visible from any position on the Earth. For more information , write us
regarding this software package.
Auroral activity is the result of atmospheric atoms and molecules being excited by
energetic electrons and ions beamed into the ionosphere. During geomagnetic subs torming,
for example, processes beyond the scope of this manual excite electrons and ions in the
magnetosphere and accelerate them. These particles follow the magnetic field lin es and
therefore penetrate mostly into the higher latitudes where the field lines make sharp angles to
the surface of the Earth. As they penetrate into the ionosphere, they reach suff iciently dense
regions of the atmosphere to collide with various atmospheric molecules and atom s. In the
collision, the energy released excites the atoms to higher energy states. When t hese atoms
drop back toward their more stable energy states, they release a photon of light that is unique
10
in color (or wavelength) for that particular atom. It is this light which we see as auroral
activity.
Auroral activity can occur in a variety of colors and patterns. Emitted waveleng ths
can range from radio to x-rays. As well as visible aurora, there are infrared au rora, ultraviolet
aurora, and x-ray aurora. Visible aurora can occur in a variety of colors. A few of the more
important colors observed are green and red (at 5577 Angstroms and 6300 Angstrom s
respectively) produced by excitation of oxygen, as well as colors from molecular bands of
singly ionized N 2 molecules. Most activity appears as greenish-blue or greyish colors.
2.4.1 Importance to HF Propagation
Most radio amateurs and even some professional broadcasters do not understand th e
significance of the auroral zones in radio propagation. The auroral zone is a ma jor region of
ionospheric instability and can result in significant signal degradation affecti ng frequencies
from the ELF to the VHF/UHF bands. Failure to consider this region of ionospheri c
instability can result in significantly flawed and inaccurate propagation predic tions and circuit
analyses.
The auroral zones are regions where electrons penetrate and deposit energy into the
ionosphere. Electrons with energy levels between approximately 1 and about 20 or 30 keV
are responsible for most of the ionization above 100 km. Of this ionization, a g ood portion of
the total ionization occurs at the lower-levels of the ionosphere near 100 km, a lthough
significant instabilities can exist above this level as well.
On an average quiet day, the auroral zone is situated near a geomagnetic latitud e of 67
degrees. However, the auroral zone is a dynamic region capable of rapid expansio n and
intensification during substorm periods. Equatorward migration of the auroral ov als is a
common feature of auroral substorms. During enhanced periods of geomagnetic acti vity, the
auroral zone expands equatorward to encompass areas of the world which are not p art of the
quiet-time auroral zone. This is one reason why some transatlantic circuits may experience
complete signal loss during geomagnetic storms while others are capable of condu cting
reasonable communications. The quality of the signal depends, to a fairly large extent, on the
position and level of activity of the auroral zones.
For these reasons, most radio propagation software do not take the auroral zone
degradation into consideration. This is unfortunate, since many thousands of peo ple who rely
on transauroral (paths which cross into or through the auroral zone) or transpol ar paths for
communicating cannot reliably use this propagation software to help determine si gnal quality.
Moreover, since the auroral ovals are offset from the rotational poles of the Ea rth, the
location of the auroral zones is continually changing and is difficult to track. This is another
reason why most propagation programs cannot (or fail to) account for the auroral zone
11
degradation, even though this is the area of the signal path where most signals will be
degraded most heavily.
PROPLAB is based on the results of scientific research and uses proven algorithm s for
computing the location of the auroral zones for any time of day, and any level o f geomagnetic
activity. The geomagnetic A-Index is the only parameter required (aside from the date and
time) to compute the position of the auroral zones. PROPLAB is therefore better equipped to
analyze and assess signal degradation through the auroral zones than many other propagation
software packages.
2.4.2 Auroral Phenomena
Auroral activity can produce several different types of phenomena, all of which can
influence radio communications. The enhanced ionization can absorb radio signals . This type
of phenomenon is known as auroral absorption. Sporadic-E is common within the au roral
zone, particularly during geomagnetic and auroral storms. Sporadic-E within the auroral zone
is known as auroral sporadic-E.
Auroral absorption (or AA) is a widely varying and almost completely unpredictab le
consequence of auroral activity. It can fluctuate widely both in time and space. The
maximum occurrence of auroral absorption appears to be just equatorward of the m aximum
level of visible auroral activity. It also maximizes in mid-morning at a fixed l ocation. It can
produce very poor to useless propagation between two points on a transauroral ci rcuit.
Auroral sporadic-E, when associated with geomagnetic storming, is also known as
"storm sporadic-E", or storm E s. The occurrence of a thick storm E s layer is known as night
E and is not uncommon in the higher latitude regions during local nighttime. Thi s type of
activity also varies widely in time and space, and can enhanced E-layer ionizati on by a
substantial amount. Often, the intense ionization observed with this type of act ivity may be
strong enough to reflect radio signals many times higher than usual. It can ther efore be a
useful tool for propagating over longer distances using frequencies in the highe r HF or even
the VHF bands - frequencies which would normally simply penetrate the ionosphere .
Electron density gradients within the auroral zones can vary significantly. Hori zontal
gradients can reflect radio signals in horizontal directions. Horizontal refract ion causes nongreat-circle-path propagation. This type of phenomenon is fairly common during d isturbed
geomagnetic and auroral periods in the auroral zones.
PROPLAB is unable to consider each of these differing types of phenomena
individually. The main reason for this is the high level of unpredictability whi ch exists for
these types of activity. Instead, PROPLAB attempts to lump all of these differin g types of
activity together to average their effects. It would also be necessary to input several different
types of data into the software for it to reliably take this activity into consi deration. Aside
12
from being unnecessary, the required inputs would be difficult for the average r adio
communicator to obtain. Reasonable accuracy is obtained from the software withou t requiring
these inputs.
2.5 Polar Cap Absorption (PCA)
Polar Cap Absorption is the result of intense ionization produced by energetic p rotons.
The protons originate from a class of large solar flares known as proton flares. These types
of flares successfully accelerate protons to a good fraction of the speed of lig ht. When these
protons reach Earth only minutes to hours later, they spiral around and down the magnetic
field lines of the Earth and penetrate into the atmosphere. The high energy of t hese protons
permits them to penetrate relatively deeply before being stopped about 40 to 80 kilometers
high. Some particularly powerful flares are capable of throwing out protons with energies in
the GeV range (most are between 1 and 100 MeV in energy). These very high energy
particles may penetrate much deeper than usual and produce what is known as a Gr ound
Level Event (or GLE) where neutron monitors at ground level experience sudden in creases in
neutron levels brought about by the deep penetration of these high-energy partic les.
PCA's typically last anywhere from about an hour to several days, with an averag e of
around 24 to 36 hours. The intense ionization of the lower ionosphere results in heavy
absorption of HF radio signals. The absorption associated with PCA is measured b y an
instrument known as a riometer (or relative ionospheric opacity meter) 3. This is basically a
radio receiver tuned to receive galactic radio noise on a frequency of about 30 MHz using a
vertically directed antenna. A higher frequency would be useful to avoid deviati ve effects,
but on higher frequencies galactic noise levels and ionospheric absorption level s decrease. On
a frequency of about 30 MHz, absorption changes of about 0.1 dB can be reliably measured.
To give an idea of how devastating PCA can be, consider what might happen to a
signal if the PCA measured over a polar region was 13 dB. This would produce att enuation
of approximately 170 dB for a 10 MHz signal reflected from the F-layer. This is sufficient to
produce complete signal loss for lower-power (non-commercial) transmissions and very heavy
attenuation of signals even from the large and powerful commercial transmitters.
PCA appears first over the polar regions. It then expands equatorward to a magne tic
latitude of approximately 65 degrees. The latitude where the ionization produced by the
incoming protons subsides, is known as the cutoff latitude. PCA therefore covers the entire
polar region down to about a geomagnetic latitude of 65 degrees. This can signif icantly
impact transpolar and even some transauroral circuits.
PCA is not related to auroral activity or geomagnetic storming. Flares which pro duce
3
−
,
. . . ., 47,
315.
13
proton events are almost always associated with coronal mass ejections which can often have
a dramatic geophysical impact. However, since the protons travel at much higher velocities
than the flare-related shockwave, the protons usually result in PCA for between 24 to 36
hours before the flare-related interplanetary shock reaches the Earth. After the shock front
passes the Earth, the density of the high energy protons gradually diminish towa rd pre-event
background levels. PCA therefore usually ends a few hours after the arrival of t he main
shocked disturbance. However, the level of geomagnetic storming which follows th e shocked
disturbance is frequently strong enough to maintain very poor to near-useless pr opagation over
the polar regions.
PROPLAB will take polar cap absorption into consideration when computing signal
quality values between two geographical points. The level of signal degradation is dependent
on signal power, and (perhaps more importantly), signal frequency. Higher freque ncies
experience less absorption than lower frequency signals during PCA. However, hig her
frequencies also penetrate the refracting ionospheric layers more easily than lo wer frequencies.
If propagation through the polar regions during PCA is required, it may therefor e be wisest to
use high transmission powers on frequencies close to the maximum usable frequenc y. PCA
does not significantly alter the refractive nature of the ionosphere. Since most of the
ionization and absorption associated with PCA occurs below the E-region (which i s the first
major refracting layer of the ionosphere), most signals still refract in the sam e manner as
would occur if PCA was not present.
PCA follows a diurnal pattern. Polar cap absorption is strongest during the day and
weakest at night. However, the difference between daytime absorption and nightti me
absorption is small (only about 2 dB). If PCA is relatively strong (ex. above 4 or 5 dB), this
difference in daytime and nighttime absorption levels may not be significant eno ugh to give
any better signal performance.
2.6 Ionospheric Radio Propagation
Most ionospheric disturbances have degratory effects on radio communications.
However, this is not always true. For example, strong signal absorption during a major flare
may completely absorb HF signals and enhance signals in the VHF bands. Polar Cap
Absorption may devastate interfering transpolar signals and thereby enhance want ed signals
from other less-affected paths. Similarly, blanketing sporadic-E can be responsi ble for
blacking out communications on a wide swath of the available HF bands, while pro viding
improved propagation and greater range for others. PROPLAB gives you the ability to
determine how to make the best use of your resources during ionospheric disturba nces of a
wide variety. However, we must first understand some of the more basic fundament als of
radio propagation through the ionosphere.
2.6.1 Ionospheric Reflection and Refraction
14
Reflection and refraction are important concepts which must be understood before
ionospheric radio propagation can be understood to any degree of usefulness. To help explore
these concepts, it is useful to adopt the idea of a ray (or single beam) of ligh t, and what
happens to a ray of light as it strikes (or passes through) various types of mat erial.
If a ray of light strikes a highly polished surface, such as a polished chrome s urface,
the rays of light that fall upon the surface are reflected. No light passes into or through the
chrome material due to the opaque nature of the polished metal. More accurately, if a ray
strikes a polished surface at an angle of 5 degrees, the reflected ray will also make an angle
of 5 degrees away from the surface of the polished material. Likewise, if a ray of light
strikes a mirror at a 90 degree angle (perpendicular to the surface of the mirro r), the reflected
ray will completely reverse direction and bounce right back along the same path that the
incoming ray took. This is why it is possible to see yourself in a mirror.
This same principle applies to almost all polished surfaces, whether opaque or n ot.
For example, it is possible to see your reflection in a store window, yet people inside the
store can look out, through the window. Reflected rays are well-behaved and easily
computed. Refracted rays are more difficult.
Refraction, in a practical sense, is the process of "bending" something. Althoug h light
travels in a straight line, light can be bent if it travels through material of varying densities.
For example, if you take a pencil and stick it into a bowl of water at an angle, the pencil will
appear to bend at the boundary between the air and the water, even though in rea lity the
pencil is solid and straight. Likewise, a ray of light which strikes water at an angle will
appear to change direction or bend, at the boundary between the air and the wate r. The
reason the pencil appears to bend is because the light at the boundary between t he air and the
water changes direction, or refracts .
In reality, a ray which strikes a surface which is not totally opaque may both r eflect
and refract the ray. Consider, for example, what happens with the bowl of water. If the
surface of the water is undisturbed, it is possible to see reflections in the wa ter (such as your
face). At the same time, it is possible to see a dime that has been placed at th e bottom of the
bowl. Rays of light are both reflected from the surface of the water, permitting you to see
your reflection, and rays of light are refracted into the water and reflected ba ck, permitting
you to see the dime.
The degree with which a ray of light is refracted depends on the speed of light within
the material where refraction takes place compared to the speed of light within the material
where the ray is originating. It also depends on the wavelength of the light tha t is passing
between the two materials. The speed of light within a material depends on the d ensity of the
material through which the light is travelling.
Light always travels more slowly through a material than it does in a vacuum. Th e
ratio of the two speeds is equal to a quantity known as the index of refraction . Thus, the
15
speed of light (v) in a material having an index of refraction (n) is given by:
v = c / n, or n = c / v
When light passes from one material to another, its frequency does not change fo r the
following reason. When light interacts with matter, the electrons in the materia l absorb
energy from the light and undergo vibration motion with the same frequency as th e light.
This motion causes reradiation of the energy with the same frequency. Hence, sin ce the
speed of light in a material is equal to the wavelength of the light (w) multipl ied by the
frequency (v = w x f), when the speed of light is less than the speed in a vacuu m (c), the
wavelength of the light is also correspondingly reduced. Thus the wavelength of light in a
material is less than the wavelength of the same light in a vacuum.
Rays which strike a surface such as water at a shallow angle might not experienc e any
refraction at all. For every refractive material, there is an angle known as the critical angle
where total internal reflection occurs. This process can be important in radio c ommunications
where signals may, for example, strike a highly-dense sporadic-E layer and exper ience total
reflection. Rays which strike the material at angles of incidence smaller than t he critical
angle are refracted, while rays which strike the material at angles larger than the critical angle
are totally reflected.
The idea of total internal reflection can be
understood by examining what happens when light passes
through a Porro prism (see Figure 2.1). A Porro prism is a
triangular slab of glass. When light passes perpendicularly
through one of the prisms sides, the ray of light does not
change direction but passes undeviated straight into the
glass. However, when the light reaches the other side of the
prism, it strikes that boundary between the air and the glass
at a 45 degree angle. For a glass/air boundary, the critical
angle is 42 degrees. Since the angle of incidence at this
boundary is larger than the critical angle, all of the light is
totally reflected toward the other side of the prism. The
same principle applies when the ray of light strikes the
Figure 2.1: Total Internal Reflection
second side of the prism. Since the ray also strikes this
in a Porro Prism
second side at a 45 degree angle, total reflection occurs
again, causing the light to strike the same surface that it first passed through , in a direction
opposite and parallel to the emergent ray.
In order to understand how radio signals are refracted in the ionosphere, it is necessary
to have an understanding of the radio refractive index of the ionosphere. Sir Ed ward
Appleton is usually the person to which the radio refractive index is attributed . Appleton was
responsible for much of the work which led to the computation of the radio refra ctive index.
It is therefore popularly known as the Appleton formula. Contributions by others have also
16
led to modified names, such as the Appleton-Lassen formula or the Appleton-Hartr ee formula.
Here, we will refer to it as the Appleton formula.
The ionosphere is composed mostly of electrons and ions. The heavier ions do not
influence the refractive nature of the ionosphere as much as the electrons. For this reason,
considering only the electrons is accurate enough when considering the refractiv e index of the
ionosphere.
As was mentioned previously, glass refracts rays of light because glass is dense r than
air. Likewise, a ray of light in open space is refracted when it penetrates into our denser
atmosphere. The same process applies to refraction of radio waves within the ion osphere.
Radio waves are simply low-frequency (or long-wavelength) rays of light.
When a ray penetrates into the ionosphere, the electron density increases rapidl y with
height until a maximum is reached approximately 250 to 400 km high. As the ray p enetrates
more deeply into the ionosphere, the increased electron density causes the ray t o begin
refracting. The degree of refraction which occurs depends on the maximum electro n density
observed as the ray travels through the ionosphere, and the frequency (or wavele ngth) of the
ray. Lower frequency (or longer wavelengths) encounter greater refraction than r ays with
higher frequencies (or smaller wavelengths).
Consider the example given in
Figure 2.2, where a radio ray with a
frequency of 10 MHz is transmitted through
the ionosphere with a starting transmission
elevation angle of 0 degrees. This
corresponds to the ray which propagates the
farthest and is directed toward the horizon.
Details regarding the contents of this figure
are given later in this manual. All of the
values at the bottom of the figure (from left
to right) are ground distances from the
origin at the left side of the screen, in
kilometers. The numbers from top to
Figure 2.2: Rays Traced through the Ionosphere
bottom on the left side of the figure
correspond to altitude above ground, again
in kilometers. The bottom panel shows the rays which correspond to transmission elevation
angles of 0, 5, 10, 15, and 20 degrees above the horizon. The upper central pane l with the
logarithmic scale shows the electron density of each of these rays as they pass through the
ionosphere. The upper central panel vertical tick marks denote the same distance scale as
shown in the large lower panel. The electron density trace farthest from the ori gin (in the
upper central panel) therefore corresponds to the ray with the zero-degree eleva tion angle in
the lower panel. In this example, the ray with lowest angle of transmission (zer o degrees)
penetrates into the ionosphere where the electron density begins to increase. As the density
17
increases the ray begins to show signs of being refracted. When the ray reaches a height of
approximately 200 km, the electron density begins to increase more rapidly along with a
corresponding increase in the refractive index. This causes the ray to bend more rapidly until
a point is reached where reflection occurs. The ray then begins a downward desce nt. As the
ray begins to descend, the electron density decreases which causes the ray to be gin refracting
again, only this time in a direction toward the ground. As the ray falls further , the level of
refraction decreases until the ray finally penetrates the lower boundary of the ionosphere. At
that point, the ray simply travels a straight line until it reaches the ground o ver 3,400
kilometers from the transmission point.
The last ray traced in the above example is transmitted at an elevation angle of 20
degrees above the horizon. It shows that as the elevation angle is increased, it becomes
increasingly difficult for the signal to return to the Earth through the process of refraction. In
this case, the signal did refract, but did not refract enough to return to the E arth.
2.6.2 Ionospheric Critical Frequencies and Heights
A great deal of information can be discerned through the study of signals that a re
transmitted and reflected vertically from the ionosphere. Ionosondes are used fo r this
purpose. There are many ionospheric sounding stations around the world. Most of these
stations are equipped with radio equipment designed to transmit signal pulses ve rtically and
listen for echoes. The principles are very similar to those that allow radar gun s to work. A
signal is transmitted vertically into the ionosphere at a specific frequency. As the signal
passes into the ionosphere, it is reflected back to the transmitting station whe re a receiver
records the characteristics and time required for the reflected pulse to return. The ionosonde
then transmits another signal pulse at a slightly higher frequency and listens f or the return of
that pulse. This process repeats in rapid succession with gradually increasing f requencies.
The frequency is sweeped from low to high frequencies.
As the frequency increases, a point
will be reached where the ionosphere will
fail to return a signal. This penetration
frequency is also known as the critical
frequency and represents the maximum
frequency that can be ionospherically
returned by a vertically propagated signal.
Figure 2.3 shows two rays being transmitted
at an 89.99 degree angle (essentially
vertical, but slightly offset from 90 degrees
so we can observe the ray behaviour more
clearly). The horizontal scale used is two
kilometers in distance. The vertical line
down the middle of the figure represents the
Figure 2.3: Penetration at the critical frequency
18
1 kilometer mark. In this example, the two rays were offset by slightly differen t frequencies
using the Sweep Frequency function of PROPLAB. The ray which returns to the grou nd uses
a frequency of 5.5350 MHz, which is very close to the critical frequency of 5.53 52 MHz.
Since the frequency of the ray is slightly lower than the critical frequency, th e ionosphere is
able to reflect the ray back to the ground. The other ray in the figure is trans mitted at the
same angle of elevation, but offset slightly in frequency to 5.5355 MHz. Since t his ray is
slightly above the critical frequency, the ray penetrates the ionosphere and esc apes into space.
Critical frequencies are very important in the study of radio propagation. They are
used to determine maximum usable frequencies for obliquely propagated radio wave s, and can
be used in many other ways to help determine other ionospheric quantities as wel l as the
general condition of the ionosphere.
Each ionospheric layer (the E, F1, and F2 layers) has its own critical frequency . Since
the maximum electron density usually occurs in the F2 layer, this layer is usual ly used to
determine the maximum usable frequency, or the frequency beyond which signals pe netrate
the ionosphere altogether. The critical frequency of the E layer is denoted: foE . Similarly,
the critical frequencies of the F1 and F2 layers are denoted: foF1 and foF2. It is important to
remember that a critical frequency always refers to signals that are directed st raight up,
toward the zenith. Another frequently used term is the plasma frequency , which is simply the
critical frequency of a section of ionospheric plasma. This is discussed in grea ter detail later.
Each ionospheric layer critical frequency occurs at a specific height that varie s
throughout the day. For example, the critical frequency of the E-layer usually r esides near
105 kilometers in height, while the critical frequency of the F2-layer lies betw een
approximately 240 and 350 kilometers in height. Since the critical frequency ref ers to the
location where maximum refraction occurs, it also corresponds to the location wh ere the
electron density is a maximum for that region (or layer) of the ionosphere.
Figure 2.4: Propagation to greater distances by raising
the height of maximum electron density
The height of maximum electron
density for the various layers of interest are
denoted: hmD (for the D-layer), hmE (for
the E-layer), hmF1 (for the F1 layer), and
hmF2 (for the F2 layer). For long-distance
communications, the F2-layer is usually the
controlling layer. Through simple geometry,
it can be shown that signals can travel
greater distances as the height of maximum
electron density increases. In Figure 2.4,
two rays are traced at different times of the
day. The first ray is traced at 03:00 UTC
and uses the same frequency and angle of
elevation as the second ray, traced three
hours later at 06:00 UTC. During this 3-
19
hour period of time, the height of maximum electron density in the F2 region inc reases by
approximately 50 km. This allows the signal to travel almost 1,000 kilometers fa rther. This
is one reason why propagation improves after sunset. The electron density in the lower
regions disappears which permits easier access to the F2-region, which is still strongly ionized
and capable of reflecting higher frequency signals over long distances. One of t he
disadvantages of night-sector propagation is the reduction in critical frequenci es. As the
evening spreads into night, the F2-layer slowly erodes and becomes less capable of reflecting
higher frequencies (in other words, the critical F2-layer frequency [or foF2] de creases). The
critical F2-layer frequency usually reaches a minimum in the hours just before s unrise.
Those familiar with ionospheric radio signal propagation may realize that radio signals
are split into two component waves: an ordinary wave and an extraordinary wave. Signals
are split into these component parts by the Earth's magnetic field. PROPLAB igno res this
splitting effect and shows you only the ray paths of the ordinary waves. Inclusi on of
calculations for the extraordinary wave would require a significantly higher num ber of
complex calculations that would make even many state-of-the-art computers choke. For this
reason, only the ordinary waves are modeled in PROPLAB. This does not limit or d iminish
the capabilities or accuracy of PROPLAB to any significant degree.
2.6.3 The International Reference Ionosphere
The International Reference Ionosphere (or IRI) is a collection of electron dens ity
height profiles that are used within computer code to generate realistic profile s of the
ionosphere. The IRI references one of two different models developed by two orga nizations:
URSI, and the CCIR. Both of these models can be used within the IRI code through the use
of numerical coefficients to describe the world-wide behaviour of ionospheric pr operties and
to generate realistic ionospheric profiles. PROPLAB gives you the power to selec t either the
URSI or CCIR models.
PROPLAB uses a corrected version of the most recent International Reference
Ionosphere. The uncorrected code failed to properly model the F1 region under so me
conditions, resulting in a discontinuity in the electron density joining the F1- layer region with
the lower-F2 layer.
The CCIR and URSI models both produce different results. The option to select on e
of these two models may improve the accuracy of some results. For most purposes, we
recommend the URSI model, although under some conditions the CCIR model may prov e to
be more accurate. If one model fails to prove accurate enough for your purposes, try the
other.
Consider the electron density profile given in Figure 2.0. This profile was prod uced
using the URSI model of the International Reference Ionosphere in PROPLAB. The
bottomside of the ionosphere (below the maximum in electron density) consists of five
20
regions. The lowest region of significance is the D-layer where electron densiti es begin to
rise, but are still confined to relatively low levels. The E-layer exists above the D-region
where there is usually a small peak in electron density. This is also where spor adic-E would
appear, as a sharp increase in electron density near the E-region peak. Above th e E-layer
exists a valley region which is small near noon, but deepens at low solar elevat ions and
during the night. Above the valley is an intermediate region that bridges the ga p between the
valley and the F-layer. Depending on season, time of day, etc, there may or may not be an
F1 region present. Detection of the F1-region is usually more difficult because of F2-region
dominance.
PROPLAB will let you produce ionospheric electron density profiles for any regio n of
the Earth and any level of geophysical activity.
2.6.4 Propagation Paths
Radio signals always try to travel the shortest distance between two points. On a
sphere such as the Earth (which is a close enough approximation), the shortest d istance
between two points is known as the great-circle distance. You can determine the great-circle
path between any two points on a globe by stretching a taught string between the two points.
For east-west northern hemisphere points, you will notice that the string appear s to form an
arc that arcs toward the northern pole before reaching the destination. Likewise , an east-west
great-circle path in the southern hemisphere travels toward the southern pole be fore arcing
back toward the destination. On north-south paths, the great-circle lies on one of the
longitude meridians. Longitudes are therefore great-circles because their planes cut through
the center of the Earth. Latitude circles do not have planes which cut through t he center of
the Earth, and are therefore not great-circles.
Radio signals that are transmitted between two east-west middle-latitude long-di stance
points have a fairly good chance of passing through the auroral zone, particular ly during
stronger periods of geomagnetic activity when the auroral zones have expanded in area.
The ionosphere is capable of transmitting signals approximately 4,000 kilometers in a
single hop. This is generally known as the maximum one-hop distance. For greater
distances, multiple hops are usually required. However, radio signals frequently travel far
beyond this one-hop distance during chordal-hop propagation or ducting. PROPLAB has the
power to determine when and how to accomplish communications using these special types of
radio propagation modes.
2.6.5 Determining Propagation Conditions
The determination of ionospheric propagation conditions between two points is no t an
easy task. Conditions can vary widely from minute to minute, hour to hour, and d ay to day,
21
and location to location. Many propagation prediction programs use algorithms th at are
optimized to improve calculation speed. In the process, they sacrifice accuracy. Others fail
to consider important parameters such as the location of the auroral zones, and thereby suffer
fairly serious inaccuracies particularly on transpolar and high-latitude paths. Consideration of
a wide host of variables is required in order to help secure accuracy and reliab ility. And even
then, the often unpredictable behaviour of the ionosphere may make it difficult to obtain
accurate results.
With PROPLAB, we decided to sacrifice speed in order to improve accuracy and
reliability, which is what most radio communicators are after anyway. And when c ombined
with the improved speed and processing power of the modern personal computer, ev en speed
might not be a problem for many people running state-of-the-art computer systems .
Here is a small list of the more important parameters PROPLAB considers when
determining propagation conditions:
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Entire path analyzed (no short-cuts).
Reduction in electron density profiles due to geomagnetic activity.
Passage through the auroral zone(s).
Winter Anomaly.
Passage through the polar region.
Influence of Polar Cap Absorption.
Equatorial Anomaly.
Sunset/Sunrise Enhancement/Degradation modes.
Influence of solar flares producing short wave fadeouts (SWFs).
Geomagnetic activity.
Sporadic-E.
Solar zenith angle.
D-region absorption.
Auroral absorption.
Date and Time.
Frequency and transmission power.
Possible radiowave inter-layer guiding modes.
Sunspot dependencies.
Varying ground-hop absorption.
Signal multipathing.
Signal spatial spreading loss.
Ionospheric focusing and defocusing.
Signal dependence on magnetic latitude.
Each of these items may be inter-related or dependent on each other in differing ways.
Determination of signal quality must carefully take these (and other) parameters and their
inter-relationships into consideration to produce results that can reflect the d iverse conditions
in the ionosphere.
22
2.6.6 Skip Distance and Maximum Usable Frequency
When tracing rays through the
ionosphere, it is useful to have an
understanding of skip distances and
maximum usable frequencies. Often, people
confuse maximum usable frequencies with
penetration (or critical) frequencies. For
obliquely propagated radio waves, maximum
usable frequencies are not equivalent to
critical frequencies.
Consider Figure 2.5 in the following
discussion. This figure shows a typical
situation where, for a given frequency, the
Figure 2.5: MUF and Skip Distance
elevation angle is increased so that the
signal eventually penetrates the ionosphere.
Notice that as the elevation angle is increased, the distance between consecutiv e rays begins
to decrease. Moreover, as the elevation increases, the ground-distance between t he transmitter
and the receiver decreases. If the elevation angle is further increased at regul ar increments, it
can be seen in Figure 2.5 that a point is reached where the signal no longer hit s the ground at
decreasing distances, but rapidly increasing distances. The point where the dist ance changes
direction (from decreasing to increasing) is known as the skip distance. It is i nteresting to
note that another side-effect of this phenomenon is the increasing concentration of rays as the
skip distance is approached. This effect is called ionospheric focusing and can result in
significantly higher signal strengths than is normally possible.
Figure 2.6: Illustration of Ionospheric Focusing
Figure 2.6 shows a
magnified view of the downgoing
rays and a typical (if not
somewhat exaggerated) example
of ionospheric focusing. Each
ray has been tagged with a
number indicating the elevation
angle used at the transmitter. It
can be seen that as the elevation
angle increases from 10 degrees
to 18 degrees, the distance of
each ray from the transmitter
decreases. As well, the
proximity of each ray to each
other ray decreases, thereby
increasing the concentration of
23
signals per unit area. As the elevation angle of the rays is increased further, a point is
reached where further increases in elevation cause the rays to increase in dista nce away from
the transmitter, resulting in signal defocusing. These rays are called high-angl e rays. High
angle rays are inherently unstable, since very small changes in elevation angle can result in
very large changes in propagated distances. For this reason, high-angle modes of propagation
are usually unsuccessful or at the very least, unstable. Signals associated with high-angle
modes are also usually fairly weak due to the defocusing which occurs. However, under
some special conditions where the ionosphere is particularly stable, high-angle rays can result
in communications at frequencies above the MUF.
Let's now go back to Figure 2.5. The maximum usable frequency in this example li es
just outside of the skip distance, near the location where the arrow points at t he bottom of the
figure. MUFs occur in regions where ionospheric focusing is usually strongest.
In this example, it can be seen that the elevation angle that coincides with the
maximum usable frequency does not coincide with the elevation angle correspondin g to the
penetration frequency. The penetration frequency is slightly higher than the max imum usable
frequency.
To help solidify the meaning of
maximum usable frequency, consider the
final example given in Figure 2.7. The
same parameters were used in this figure as
those that were used to produce Figure 2.5,
except that a fixed angle of elevation of 9
degrees is used while varying the frequency.
The location denoted by the arrow at the
bottom of both of these figures is the
location of the MUF. In these examples,
the MUF is approximately 13.2 MHz.
Figure 2.7 sweeps the frequency from 10
MHz to 14 MHz in steps of 0.5 MHz (or
Figure 2.7: Frequency Sweep showing concept of MUF
500 KHz), and shows that for an elevation
and penetration frequency
angle of 9 degrees, the maximum usable
frequency is approximately 13.0 MHz
(corresponding to the ray that hits the ground where the arrow points). This fre quency differs
from the penetration frequency by about 1.0 MHz, for as Figure 2.7 illustrates, the penetration
frequency occurs at about 14.0 MHz. The high-angle rays are those which would be reflected
by the ionosphere between the MUF of 13 MHz and the penetration frequency of 14 MHz.
2.7 Ray Tracing Techniques
PROPLAB PRO Version 2.0 is equipped with two major ray-tracing techniques that
24
compute how signals propagate into and through the ionosphere. These two methods will
hereafter be called the simple and comprehensive (or complex ) ray-tracing techniques.
The simple ray-tracing technique is faster than the comprehensive method, but is much
less accurate. Nevertheless, it produces statistics which are of fundamental imp ortance such
as the distance the signals travel through the auroral zones, the behavior of si gnals as they
interact with regions of sporadic-E, and much more. This method does not include effects of
the Earth's magnetic field or the process of electron collisions with neutral pa rticles in the
atmosphere (a very important parameter for determining ionospheric absorption an d accurate
ray paths). However, it does estimate the effects of geomagnetic activity on rad io signals.
The comprehensive ray-tracing method is a sophisticated and extremely powerful r aytracing engine that should be used to accurately trace signals through the ionos phere. It will,
if desired, include effects of the Earth's magnetic field and electron collision s with neutral
particles. It will also optionally trace signals through a realistic three-dimen sional ionosphere.
However, in order to keep the program which is responsible for these sophisticat ed functions
within the memory constraints imposed by the DOS environment, the rays must be t raced
through an undisturbed geomagnetic field. Therefore, the geomagnetic A-index is not used in
the complex ray-tracing technique. However, the effects of geomagnetic activity can be
approximated by inputting an effective sunspot number that is correlated with solar activity
and geomagnetic activity. Similarly, due to memory constraints, the complex ray-tra cing
method cannot include effects of the auroral zones. These are the two most impor tant
parameters which the complex method does not include in its computations. Howeve r, the
increased accuracy obtained by using the complex method outweighs the influence of the
auroral zones and geomagnetic activity. Using the complex method, the influence of
ionospheric tilts, chordal hop propagation, ducting and much more can be accurat ely displayed
on-screen. These effects are global in nature and affect all signals travelling everywhere,
unlike the effects of geomagnetic and auroral activity which tend to be localize d more to the
high and polar latitude regions.
Throughout this manual, references will be made to the simple or complex techniques.
Many of the available options apply to only one of these techniques. Others appl y to both. It
is important to know which options apply to which techniques so that PROPLAB is
appropriately set up.
25
SECTION 3 - PROPLAB
The file "README.NEW" which is installed with PROPLAB may
contain information that is not contained in this manual.
Consult that file for information not appearing in this manual.
3.1 Installation of PROPLAB
To install PROPLAB on your hard drive, insert the program code disk into drive A :
and type: "A:INSTALL". After supplying any necessary information, PROPLAB will b egin
installing the software in the directory "C:\PROPLAB" on your hard drive. Part o f the
installation procedure includes generating maps centered on your particular geog raphical
position. Each of these differing maps can be used by the PROPLAB software. In o rder for
some of the functions of PROPLAB to operate properly, it is imperative that you install at
least one map: a Plate Carree map must reside in your map library for these func tions to
work.
IMPORTANT: PROPLAB PRO Version 2.0 will now construct full-color global maps
where the ocean is colored blue and the land is colored brown with large lakes also colored
blue. This new enhancement provides aesthetically pleasing maps compared to themonocolor maps used in previous releases. If you do not want to use these new full-color maps
but would rather stick with the older style maps, use the older map management utility on
your disk named "MKMAPV1.EXE" to create the older-style map library. You can now
also customize the colors of the maps (consult Section 3.2 of this manual for more
information).
FOR INDIVIDUALS UPGRADING TO VERSION 2.0: If you have an old version of
PROPLAB on your computer, you MUST DELETE EVERYTHING in the old PROPLAB
directory before installing Version 2.0 of PROPLAB PRO. There are some significant
changes to the way PROPLAB handles some of the files and utilities. In order forit to be
properly installed, all old versions must be completely deleted from your hard-drive (unless
you are installing PROPLAB PRO Version 2.0 in a different directory). This doesNOT
apply if you are installing PROPLAB PRO Version 2.0 in a directory that is completely
separate from the old version. However, any DOS environment variables that referto the
old version must be modified to point to the new version after it has been successfully
installed.
If you previously purchased our Professional Dynamic Auroral Oval Simulator, you
will notice that the older mono-colored maps are used. However, the format of th e map files
are identical. Those who use our Auroral Oval Simulator can therefore see whethe r they want
to use the full-color map databases by copying the "MAPS.LIB" file from the PROP LAB
directory into the directory containing the Auroral Simulation Software.
26
After the installation procedure is complete, you can execute PROPLAB from your
MSDOS command prompt. PROPLAB PRO has not been tested very extensively under
Windows 95 (in a DOS mode). It does, however, work for the most part under Windo ws 3.1
in DOS mode. Keep in mind, however, that PROPLAB was developed for the DOS
environment. It will probably be ported over to Windows 95 in later releases.
3.2 Running PROPLAB, Changing Colors, and Setting Up the Printer
There are three different ways to execute PROPLAB from the DOS command prompt.
You may type "PROPLAB" and press ENTER, or you can type "PROPLAB -" and press
ENTER. The first command loads and runs PROPLAB, permitting you to see the openi ng
title page, etc. The second command loads PROPLAB, but skips displaying the titl e page and
instead takes you directly to the main menu of PROPLAB. Use either of these two methods
to run PROPLAB normally. However, the first-time you run PROPLAB, you should run it by
typing "PROPLAB" and pressing ENTER. The first time PROPLAB is run, it gathers
information about your current system configuration and writes this information to a file for
future reference. After you have run PROPLAB once, you can select any of these t hree
execution methods.
The third method of running PROPLAB permits you to change the colors (text and
graphics) used in PROPLAB. To do this, type "PROPLAB SETCOLORS" and press ENTER.
PROPLAB then asks you to type in the new colors to be used by PROPLAB.
The VGA graphics employed by PROPLAB PRO allow up to 16 different colors to be
displayed at the same time. PROPLAB PRO Version 2.0 lets you change any of these colors
to any ratio of RGB (Red Green Blue) values. It is therefore possible to change any of the
colors used by PROPLAB's graphics plots to any shade or color desired. For examp le, an
RGB combination of 0,0,0 (Red=0, Green=0, Blue=0) results in the color BLACK, si nce all
three primary colors have an intensity of 0 (or dark). The maximum RGB value tha t can be
input is 63, which represents a brilliant intensity. For example, an RGB value o f 0,63,0 will
produce the brightest GREEN color possible. A value of 0,32,0 will produce a GRE EN color
that is half as bright as the previous example. This will appear on-screen as a darker colored
GREEN.
PROPLAB PRO asks you if you want to reset the RGB colors to their default values .
If you have experimented with the RGB colors and need to reset the colors back t o their
originals, respond affirmatively to this prompt (which is only asked if you exec ute PROPLAB
using the "PROPLAB SETCOLORS" command at the DOS prompt.
To change the graphics color BLACK (which is also the background color) to WHITE
(so all graphics are drawn with a white background and black lettering), change the RGB
values for the color BLACK from 0,0,0 to 63,63,63. Similarly, change the RGB val ues for
the color WHITE from 63,63,63 to 0,0,0. To make the color RED a dark green, you might
27
change the RGB values for the color RED from 63,0,0 to 0,25,0. Almost any other color can
be created by using varying ratios of Red to Green to Blue. For example, you cou ld change
the color of YELLOW to a custom color using an example RGB value combination of:
14,48,36.
The changes you make to the colors of PROPLAB are reflected in all of the module s
of PROPLAB, including the Map Management System (MAKEMAP.EXE). So, if you want
to recreate your map database using different map colors, you simply need to exe cute
PROPLAB via "PROPLAB SETCOLORS" and then change the RGB values of the
appropriate map colors. For example, to make the oceans a GRAY color instead of blue, you
would change the RGB value for the color BLUE to an RGB combination such as 40,4 0,40.
Then rerun the MAKEMAP.EXE utility to reconstruct the desired maps using the new color.
Keep in mind that the all other PROPLAB modules that use the color BLUE will now use
the color of GRAY instead. So the colors you change may have side-effects with he
t colors
used in other sections of PROPLAB.
Some of the subprograms within PROPLAB are large. For this reason, the
PROPLAB.EXE program basically controls the main functions of PROPLAB, sets up th e
relevant parameters, contains the main menu and submenus, and redirects control to the other
subprograms when appropriate.
Most of the functions in PROPLAB are computation-intensive and require at least a
386 computer to operate at a decent speed. However, even some 386-based systems (ex.
those without math coprocessors) may operate relatively slowly while using this software.
For this reason, systems equipped with math coprocessors or 486-or-better based computers
are much better equipped to handle the large quantity of complex floating-point calculations
required for many of the functions of this package. Use of coprocessors will sig nificantly
speed up operations and are recommended for use with this software. PROPLAB will operate
fine if you don't have a math coprocessor in your system. It will simply take mo re time to
complete some of the functions.
We have made every effort to test this software for bugs. Although we can't prom ise
that all of the bugs have been corrected, we hope they have. If you find a bug i n the
software, we would appreciate it if you would write to us and notify us of the p roblem.
Inform us of the type of computer system you have, hardware configuration, type and version
of the disk operating system you are using, as well as any other pertinent infor mation that
will help us locate any potential problems in the system. We will do our best to correct any
problems that are found as quickly as possible. Alternatively, send bug reports to us on the
Internet via: [email protected] or [email protected]
PROPLAB will print graphic-screens directly to your dot-matrix printer. But befo re
this can be accomplished, PROPLAB's printer control file "PROPLAB.PTR" must be
modified to work with your particular printer. All of the instructions necessary to alter this
file are contained in that file. Edit it with a standard word processor or text editor to meet
28
your printers requirements. This printer control file is only intended for dot-m atrix printers.
If you have a laser-printer (PostScript), you should be using the command to cre ate a
PostScript image file. Do this by pressing "P" at any of the graphics screens pr esented by
PROPLAB. Then exit to DOS and send the saved PostScript file (which contains the
extension .PS) to your printer.
At any of the graphic-screens presented by PROPLAB (except the Broadcast Coverag e
Map screens), pressing "H" (short for Hard copy) will cause PROPLAB to begin sen ding the
contents of the current graphic screen to your dot-matrix printer.
If you fail to modify the printer control file "PROPLAB.PTR" correctly for your
printer, you may see garbage printed instead of an accurate rendition of the gra phic display.
The initialization strings are of greatest importance. Make certain that the ini tialization
strings contain (if needed by your printer) the correct size of the printed line s and that the
given size matches the "LOCKSIZE" parameter (read the file "PROPLAB.PTR" for mor e
information). Failure to do this will cause improper printer operation. Those wi th laserprinters may find it easier to simply convert the graphic screens to a PostScrip t compatible
format by pressing "P" (Postscript) at any of the graphic screens. This is the o nly way to
reproduce the broadcast-coverage map screens which are heavily color-coordinated .
Consult your printer manual for all of the initialization string codes which sho uld be
used in the printer control file. Each printer usually differs, which is one rea son why a
printer control file is used. It permits essentially universal compatibility wit h printers.
If you have a laser-printer, don't use the "H" command as this is optimized only for
dot-matrix printers. For later printers, create a "P"ostScript version of the gr aphic screen.
After it has been saved to a PostScript file (containing the extension ".PS"), e xit to DOS and
copy the PostScript file to your laser printer.
3.3 Setting the Required Parameters
The eighth choice of the main menu is an Options Menu. This is where you setup
most of the parameters required to run PROPLAB. It is where you define the opera ting
frequency, transmitter power, date and time, location of the transmitter and rec eiver, sunspot
number, etc. The options in this section should be adjusted to fit your specific ations before
you perform any of the major functions of PROPLAB, such as ray-tracing or determ ining
MUFs, etc. Here, we will briefly describe the available options.
3.3.1 Setting the Transmitter/Receiver Locations and Time Zones
PROPLAB requires the geographical position of the transmitter and receiver in or der
to work. The first two options of the Options Menu let you change these paramete rs to fit
your needs.
29
Geographical positions should be entered in decimal notation (not in degrees, mi nutes,
and seconds notation). That is, if your geographical location is 50 degrees nort h latitude, 30
minutes and 45 seconds, you would enter your geographical position as 50.5125 - not as
50.3045. In addition, all latitudes north of the equator must be entered as posi tive numbers,
while those latitudes south of the equator should be entered as negative numbers .
Geographical longitude values can be measured in decimal degrees west or east of
Greenwich. For example, Denver Colorado is located at approximately 105 degrees west
longitude and would therefore be entered in PROPLAB at a position of 105 degrees . Again,
decimal values must be used, not degrees minutes and seconds. Sydney Australia i s located
at 150 degrees east longitude or 210 degrees west longitude. If measurements are given in
degrees east of Greenwich, negative values must be used. That is, if Sydney's ea stern
longitude value were entered in PROPLAB, the value -150 would be used.
PROPLAB requires knowledge of the time zone of the transmitter so that if local time
is used, PROPLAB can compute what the local time is at the receiver. PROPLAB has the
ability to automatically guestimate the time zone of the transmitter by dividing the
geographical longitude of the transmitter by 15 degrees (since the Sun travels 1 5 degrees of
longitude per hour). Although this is usually accurate enough, some regions may not be in
easily divisible time-zones. PROPLAB therefore gives you the option of having th e computer
automatically calculate the time zone for you, or allowing you to input the time zone
manually. If you choose the latter, time zone information must be entered as a p ositive or
negative integer reflecting the time-difference between Universal time (UTC) and local time
for the current transmitter geographical location. Positive integers are used fo r locations that
are west of Greenwich. Negative integers are used for locations that are east of Greenwich.
For example, Denver Colorado is west of Greenwich and therefore uses a positive integer
value of +7 hours, since the difference between local time and Universal time is 7 hours.
Similarly, Sydney would use a value of about -10 hours. During daylight savings time, it
may be necessary to include the adjustment in this time-zone input.
When PROPLAB is configured to automatically compute the time zone information,
the acronym "AutoZone" is set to ON. The status of this "AutoZone" variable can be
determined at the main Options Menu. If it is set to OFF, manual input of time-z one
information is required each time the transmitter location is changed.
PROPLAB permits the selection of geographical locations by one of three differen t
methods: by numerical entry, name entry, or grid-coordinate entry. Numerical ent ries are
those where the actual latitudes and longitudes are typed. PROPLAB will also sea rch through
a geographical dictionary of locations (city names or other aliases) and accept matching
entries, if you have enabled the AutoQTH function. For example, if the geographical
dictionary contains "Orlando"'s geographical coordinates, you can inform PROPLAB to
automatically grab Orlando's coordinates from the geographical dictionary by sim ply typing
"Orlando" or "orlando" or "ORLANDO" or "oRLaNDo" at any of the prompts requestin g the
"Latitude or Site Name". The names are case-insensitive.
30
The geographical dictionary is located in the file "PROPLAB.LOC". This is a simp le
text file that can be edited with a standard text editor or word processor. Line s prepended
with an asterisk "*" are treated as comments. Each line of this file must follow this format:
CITY NAME=LATITUDE,LONGITUDE,TIME-ZONE
For example, "Philadelphia=40.0,75.0,-5" is a valid entry defining the approxima te location of
Philadelphia. At any of PROPLAB's prompts requesting a Latitude or Site Name, yo u could
type "Philadelphia" and PROPLAB would automatically enter the latitude and longi tude
values as 40.0 and 75.0 respectively. The "-5" defines what time-zone Philadelph ia is located
in. In this case, Philadelphia is -5 hours different than Universal Time, or the time reckoned
from Greenwich England. Mountain Standard Time is "-7" hours. Pacific Standard T ime is
"-8" hours, etc.
The third method of entering in locations is using the grid-location method. Thi s
method is popular amongst people who frequent the VHF and UHF bands. This method
divides the Earth into hundreds of small 2-degree-wide squares. Each square is g iven a
special fixed name or designation such as "DN43ah". To use grid-square designati ons at the
prompts requesting Latitudes or Site Names, simply prepend the grid-square name with an
exclamation mark "!". For example, "!DN43ah". PROPLAB will then automatically co nvert
this grid-square name into the appropriate geographical latitude and longitude c oordinates.
3.3.2 Graphically Setup Transmitter/Receiver Locations
If your system is equipped with a mouse, you can graphically set the position of the
transmitter and receiver using the third option of the Main Menu in PROPLAB, "Se tup
Sporadic-E / Xmit-Recvr Locations". To use this feature, a Plate Carree map proj ection must
exist in the map library. If the map exists, it is displayed on-screen along wit h the location of
the mouse cursor, the location of the auroral zones, the location of the sunrise /sunset
terminator (or grayline), and the location where the Sun appears directly overhe ad.
PROPLAB PRO also lets you plot an additional line that marks the regions of the world
where the sun is a specific number of degrees above or below the horizon. For ex ample, you
can now instantly determine the regions of the world where evening and morning t wilight is
beginning or ending by telling PROPLAB to plot a line which marks the locations where the
sun is, say, 12 degrees below the horizon. This is accomplished by specifying a value of -12
as the angle for the sun. Negative values represent angles below the horizon. Po sitive values
represent angles of the sun above the horizon. A value of zero then, represents the locations
around the world where the sun is exactly setting (or crossing the horizon). Thi s is an
extremely powerful function that lets you visually determine precisely the proxi mity of your
chosen radio path to the various zones of influence.
PROPLAB PRO Version 2.0 is now equipped with another major function which will
let you plot these various zones of influence in real-time ! Consult the appropriate section of
this manual dealing with the real-time mapping system.
31
To set a new transmitter/receiver location pair, move the mouse cursor to the po sition
of the transmitter and click on the left mouse button to mark that location. The n, move the
mouse to the location of the receiver and click on the right mouse button. The g reat-circle
path between the two points will then be traced on-screen along with updated pos itions of the
auroral ovals, the grayline, and the Sun if local time is being used.
You can alternatively keep the location of the transmitter constant and change t he
position of the receiver by moving the mouse to the new location of the receiver and clicking
on the right mouse button. This will only change the position of the receiver an d will leave
the transmitter location constant.
This powerful feature of PROPLAB permits you to instantly determine what signal
paths might cross into the influential auroral zones, or what signal paths to us e along the
grayline, etc. The usefulness of this feature goes far beyond the simple establi shment of
transmitter and receiver locations. As you become more skilled in this use of th is software,
you will discover the greater importance of these other included features.
You can save copies of these screen images to disk in one of several formats. By
pressing "G", you can save the screen to a GIF image file. By pressing the "P" k ey, you can
save the screen image to a PostScript-compatible file for sending to a laser-pri nter. And by
pressing "S", you can save the screen image to a special format that can later b e used by
PROPLAB to superimpose other information on. For example, you could superimpose
contours of maximum usable frequencies on the map used to select transmitter and receiver
locations. The additional information included on these maps (location of the au roral zones,
location of sporadic-E, the traced path between the transmitter and receiver, gr ayline, etc)
would provide a wealth of indispensable information when combined with contours of
ionospheric properties. See Section 4 for more information regarding these featu res.
3.3.3 Ray Tracing Speed, Path Type, and Termination Mode
When performing ray-tracing functions in PROPLAB using the simple technique , you
can set the speed with which PROPLAB traces rays by using the third option of th e Options
Menu. This value is preset to 10, which is a nice round arbitrary figure that pr ovides decent
speed of operation and accuracy for systems that are both equipped with and with out math
coprocessors.
Lower values cause PROPLAB to trace rays through the ionosphere in smaller
increments. This may increase the accuracy of the results slightly, but will als o slow down
the speed of operation by increasing the number of required calculations. Likewi se, larger
values will speed up traced rays by tracing through the ionosphere in larger ste ps. However,
the results will become less accurate as larger ray tracing speed values are use d. This is
particularly true for signals that must pass through regions of sporadic-E, wher e density
increases rapidly over a short height interval. A judicious choice of ray tracin g speed is
32
required when considering the effects of sporadic-E on traced rays. If a value t oo large is
used, the signal may completely step over the region containing sporadic-E. For this reason,
smaller values of around (or less than) 10 are recommended when taking sporadic- E into
consideration.
You can also define the type of path you want traced from within this option. Th is
only applies to the simple ray-tracing technique. To use Long Paths, select "L". To use
Short Paths, select "S". The complex ray-tracing method cannot trace rays using long-paths.
It always traces rays using the shortest distance between the transmitter and th e receiver. It
can therefore only trace rays out to a distance of 20,000 kilometers, which is t he
circumference of half of the Earth and is the greatest short-path distance betwe en two points.
The Termination Mode applies to both of the available ray-tracing techniques and tells
PROPLAB when you want it to stop tracing rays through the ionosphere. If the sig nal
strength or quality becomes degraded to the point where it is useless or "blacke d-out", a white
"X" is stamped on-screen at the point where the signal vanishes (the X is only d isplayed
when using the simple method). PROPLAB will normally continue tracing the ray through
the ionosphere even though the signal quality or strength is at the blackout con dition. If you
want PROPLAB to stop tracing rays whenever the blackout condition is reached, yo u can
change the termination mode to stop ray-tracing if this occurs. For the complex ray-tracing
technique, this occurs when the signal strength reaches zero decibels (dB). This will help
speed up ray-tracing sessions by ignoring signals that lose all power.
3.3.4 Choosing Ionospheric Models (URSI or CCIR)
PROPLAB is integrated with two different ionospheric models while using the simple
ray-tracing technique and six ionospheric models while using the complex ray-tracing
technique. These models are discussed below.
Ionospheric models are necessary in order to describe the characteristics of the
ionosphere around the world. These models effectively describe the electron dens ity of the
ionosphere for any location around the world and level of solar activity. They a re of critical
importance to PROPLAB, because it is the density of electrons in the ionosphere that is
responsible for the refraction (and reflection) of radio signals through the ion osphere.
3.3.4.1 Models to use with the Simple Ray-Tracing Technique
The two available models that can be used with the simple ray-tracing technique are
known as the URSI and CCIR models. Both models are accurate and reliable and are proven
performers and produce similar results. There is no real preference of one over the other.
The choice of which model to use is up to you. The default has been arbitrarily set to the
URSI model.
33
3.3.4.2 Models to use with the Complex Ray-Tracing Technique
The complex ray-tracing technique is able to use one of up to six different iono spheric
models, described as either two-dimensional or three-dimensional as follows. You can select
which model to use from Main Menu Option #8, Suboption #18, Choice #4.
Model #1: URSI Two-Dimensional Model
This model is based on the URSI ionospheric model and describes the ionospheric
characteristics for a given point on the Earth up to an altitude of 1,000 kilome ters. It does not
describe ionospheric characteristics in three-dimensions and therefore should on ly be used when
performing comprehensive single-hop ray-tracing plots. The two-dimensional comprehensive raytracing technique can only reliably handle single-hops because only one two-dime nsional
ionospheric profile is generated. On subsequent hops using the two-dimensional m odel, the same
ionospheric profile is used which represents the characteristics of the ionosphe re at the midpoint
of the first hop. Subsequent hops therefore use the same ionospheric profile whi ch differs from
reality. For multi-hop paths, use one of the three-dimensional models below.
Model #2: URSI Three-Dimensional Model
This model is based on the URSI ionospheric model and describes the ionospheric
characteristics in three dimensions up to 1,000 kilometers in height. This model (or another
three-dimensional model) should be used when accuracy is important, when chordal hop
propagation or ducting is to be analyzed, or when there may be more than one gro und reflection
on the way to the receiver.
Model #3: CCIR Two-Dimensional Model
This model is based on the CCIR ionospheric model and has the same limitations a s those
that describe Model #1. Use the CCIR Three-Dimensional Model for multi-hop paths , chordal
hop paths, ducting, etc.
Model #4: CCIR Three-Dimensional Model
This model is the three-dimensional version of the CCIR ionospheric model and is
identical to Model #2, except it uses the CCIR method of computing ionospheric c haracteristics.
Model #5: Quasi-Parabolic Two-Dimensional Model
This model is very similar to the ionospheric profile models employed by other s impler
propagation programs. It uses a standard parabolic equation to describe the elec tron density
34
throughout the ionosphere. Use of this model demands a fair bit of knowledge of ionospheric
electron density shapes and a familiarity with the standard parabolic profile eq uations. Before
this model can be used to produce an ionosphere in which rays can be traced, sev eral options
must be defined in the comprehensive ray-tracing options menu (Main Menu #8, Sub option #18).
In particular, you must define the critical frequency of the F2 layer at the mid point of the path
(if this is unknown, you can use the CCIR or URSI model with PROPLAB to print ou t the
predicted critical F2-layer frequency (use Main Menu Option #7 after defining th e location of the
transmitter and receiver)). You must also specify the thickness of the F2-layer and the height
where the electron density reaches a maximum in the ionosphere. These parameters will be
discussed in greater detail in the section which deals with these settable optio ns. This model is
only valid for single-hop paths.
Model #6: Alpha-Chapman Two-Dimensional Model
This model is similar to Model #5 and requires the same type of information. It is also
only valid for single-hop paths.
3.3.4.3 The "Right" Model to Use
There is no "right" or "wrong" ionospheric model. The model you use will usually be
dictated by exactly what you require. However, if you are not sure what you need or which
model you should select, use one of the three-dimensional models. They tend to b e a little more
time-consuming to set up but are not as prone to produce confusing results. More importantly,
the results they produce are more accurate and easier to interpret.
Generally, for most applications, either the URSI or CCIR three-dimensional mode ls will
be of greatest value. The two-dimensional models should only be used if you are tracing signals
through the ionosphere that you know will never need to be traced beyond one hop . That is, the
signals should never be reflected by the ground and back into the ionosphere bef ore reaching or
nearing the reception point. Paths beyond 4,000 kilometers definitely should not use the twodimensional models. Instead, one of the three-dimensional models should be used.
Models #5 and #6 are oriented more towards professionals who know the capabiliti es and
uses for Quasi-Parabolic and Alpha-Chapman electron density equations. If you ar e not familiar
with these models, selecting them may prove to be problematic and produce unreal istic results.
In other words, if ever in doubt, use either the URSI or CCIR three-dimensional models.
They will automatically handle all of the things which the two-dimensional model s do not, such
as recomputing electron density profiles at each point along the traced ray, etc .
3.3.5 Setting the Operating Frequency
35
The fifth option of PROPLABs Options Menu applies to both the simple and the complex
ray-tracing techniques. It lets you define the operating frequency of the transm itter (in MHz).
This is a very critical parameter. PROPLAB could not function without it, for ob vious reasons.
The operating frequency must be entered in units of megahertz (MHz). For example , a
transmitter that is set up to operate on the 40 meter shortwave band would use a frequency of
between approximately 7.0 and 7.3 MHz.
There are no real limits applied to the operating frequency. Frequencies in the Medium
Frequency bands or frequencies in the VHF bands can be input. However, please no te that
frequencies below about 2 MHz may produce increasingly error-prone results with the simple raytracing method. The complex method is better able to accurately handle these wide ranges in
frequencies since they use equations which accurately model the physical propert ies and behavior
of signals of almost any frequency.
3.3.6 Setting the Date/Time and Auto-Sunspot-Number Computation
This option applies to both of the ray-tracing methods.
The sixth option of the Options Menu permits you to define the date and time. En ter the
date in the format YY,MM,DD and the time in the format HHMM. For example, 08 Dec ember
1993 at 4:30 pm would be entered (using local time) as: 93,12,08 for the date, a nd 1630 for the
time. Be sure to enter the time according to how you have setup PROPLAB. If loca l time is
used, use local time. If UTC time is used, use Universal time.
This option also allows you to enable or disable the automatic computation of th e sunspot
number if you also are using the BCAST Solar and Geophysical Database Management Software.
If you are not using this software, this feature should be disabled to permit ma nual entry of the
sunspot number. If you have the BCAST software installed and enter a date which is in the
BCAST database, PROPLAB will automatically attempt to compute the 12-month mean sunspot
number from the BCAST database (for median results, the 12-month mean sunspot nu mber is
recommended). It will also extract the geomagnetic A-index for the given date fr om the BCAST
records and automatically modify these parameters for the new date chosen.
If you want to maintain full control over what values are input, disable this au tocomputation feature and enter in the data manually. If this feature is enabled, you will notice a
time-lag while the system tries to retrieve the necessary data from the BCAST da tabase. If
PROPLAB cannot locate the BCAST database, it will abort without any changes. The DOS
environment variable "BCAST" should point to the directory containing the databa se.
3.3.7 Setting the Transmitter Power
36
This option applies to both of the ray-tracing techniques.
NOTICE: Previous versions of PROPLAB required the input of a "relative transmitter
power" figure. PROPLAB PRO Version 2.0 no longer asks for this. It instead requi res the
actual power of the transmitter in Watts. For example, a 10 kilowatt transmitter would be
entered as 10000.
This function of the Options Menu lets you set the transmitter power (in watts). It is used
by both the simple and the comprehensive ray-tracing techniques to compute the s ignal strength
of the ray being traced.
The simple ray-tracing technique produces signal strength results that are not r igorously
computed, but they do contain estimated effects of auroral absorption and other anomalies that
can affect signals.
The comprehensive ray-tracing method rigorously computes signal strength values based
on actual computed ionospheric absorption values, signal spreading loss, etc. Th e comprehensive
technique will produce results that are more closely aligned with reality than t he simple method
(except perhaps during geomagnetic storms, as geomagnetic activity and auroral a ctivity are not
taken into consideration with the comprehensive technique, as discussed earlier) .
3.3.8 Setting Ranges and Steps
This option applies to both ray-tracing techniques.
PROPLAB often requires a range of values or step values to use in performing cer tain
functions. For example, when ray tracing signals from one point to another using elevation
angles of between 0 and 20 degrees, these values would be modified to cover the range and step
values needed to complete the tracings.
In most instances, you will not need to use this choice of the Options Menu. The
software will automatically prompt you for the appropriate ranges and steps.
3.3.9 Selecting Local or Universal Time
This option applies to both ray-tracing techniques.
Using this choice of the Options Menu, you are able to change the type of time u sed in
PROPLAB. Local time is the time you set your alarm clock to when waking up in th e morning.
Universal time is reckoned from Greenwich England. It is the time on which all o ther times
around the world are based. Universal time is the same for everyone, everywhere. Universal
time can be determined anytime of the day, to the second, by listening to radio stations WWV
37
and WWVH on the shortwave frequencies 2.5, 5.0, 10, 15, and 20 MHz. There are ot her equally
accurate clocks on the broadcast bands, but those mentioned above are the most a ccessible.
Select whichever type of time you need to use. If you use local time, PROPLAB wi ll
convert it when necessary to equivalent Universal Time using the Time Zone infor mation
described earlier. All dates and times entered into PROPLAB will be reckoned acc ording to the
type of time selected here.
3.3.10 Setting the Geomagnetic A-Index
This option is only used by the simple ray-tracing method and several of the supporting
PROPLAB functions, such as the real-time mapping system.
The geomagnetic A-index describes how active the geomagnetic field is at a given time.
The value which should be used here can be found by listening to radio stations WWV or
WWVH at 18 minutes past each hour on the frequencies 2.5, 5, 10, 15, or 20 MHz. In some
instances, it may be useful to convert the given K-index value (which is measure d every 3 hours)
to an associated A-index value. This can be done using the table of K/A Indices given in Section
2.3.1 (The Geomagnetic K-Index). For example, since a middle-latitude K-index of 5 is
associated with an a k index of 48, the A-index for that 3-hour interval would be 48. Using Kindices in this manner to help compute shorter-term A-indices may (or may not) r esult in better
short-term determination of propagation conditions. Success using this technique may vary from
one event to another.
Overall, PROPLAB is optimized to use the 24-hour A-index value given by WWV and
WWVH. Quiet geomagnetic and ionospheric conditions are assumed to exist with A-i ndices
between about 5 and 10. Input values of 5 can also be used to produce monthly me dian results.
For example, to create monthly median maps of critical frequencies or Maximum Us able
Frequencies, an A-index value of 5 or lower should be used. Use of higher A-indi ces may give
results that are not median in nature.
A "median" value is one which occurs 50% of the time.
3.3.11 Setting the Sunspot Number or Solar Flux
This option is used by both of the ray-tracing techniques.
PROPLAB permits the entry of either the sunspot number or the 10.7 cm (2800 MHz)
solar radio flux. This information is used to help determine the strength (and i ntensity of
ionization) of the ionosphere.
To input the sunspot number, simply type in the number at the prompt. To input t he 10.7
38
cm solar radio flux value, prepend an "F" (for Flux) to the number you type. An upper or lower
case F will work. For example, to input a sunspot number of 60, type "60" at the prompt. To
input a solar flux value of 145 type "F145" or "f145".
If you enter a solar flux value, PROPLAB immediately converts that value to an
equivalent sunspot number. That sunspot number is then used in all PROPLAB calcu lations.
You can obtain the 10.7 cm solar radio flux value from radio stations WWV or WWV H
at 18 minutes past each hour on one of the frequencies: 2.5, 5, 10, 15, or 20 MH z. For greater
accuracy, it is usually wise to enter the average sunspot number or solar flux v alues for the last
week or more. The ionosphere reacts more slowly to changes in solar radiation. A verage values
are therefore usually more reliable than daily values.
For monthly median results, the 12-month mean sunspot number or 12-month mean so lar
flux value must be given. If you are using the BCAST software and have enabled t he Auto-SSNCalculation feature, PROPLAB will automatically search the BCAST database for th e given date
and compute the 12-month mean sunspot number for you (when you change dates).
3.3.12 Selecting the Number of Allowed Hops
This option is used by both of the ray-tracing techniques.
When ray-tracing signals between two distant points, it may be necessary for the
ionospherically reflected signal to make more than one ground-hop to reach the d estination. This
option lets you define exactly how many hops are permitted when ray-tracing sign als. If you hit
ENTER at this prompt, PROPLAB will automatically permit as many ground-reflectio n as
necessary for the signal to reach the destination. Once the destination has been reached (or
surpassed), no more ground-hops are permitted. If you enter a value at this prom pt, that value
will be used as the maximum number of allowed hops. As soon as the number of hop s reaches
this value, tracing for that particular ray stops.
3.3.13 Selecting PROPLAB's Quick or Normal Modes
This option is only valid when using the simple ray-tracing method.
When tracing signals through the ionosphere using the Normal Mode, the upper
information panel is continually updated as the signal is traced from the transm itter to the
receiver. When the software is running in the Quick Mode, the upper information panel is not
updated. Only the simultaneous electron density curve is updated in this mode. T his has two
major effects: it reduces the number of calculations and time-consuming screen-u pdates, and it
significantly speeds up the tracing of the rays without sacrificing accuracy. On e major
disadvantage of using the Quick Mode is the loss of the computation of signal qu ality. Functions
39
that rely on signal quality data, such as the generation of Broadcast Coverage S ignal Quality
Maps, will not work properly if the traced signals are done using this Quick Mod e function.
For greater speed when using the Quick Mode, it is necessary to increase the ray tracing
speed of the software (see Section 3.3.3).
3.3.14 Selecting Plane or Spherical Grids
This option is only available while using the simple ray-tracing technique.
PROPLAB uses a spherical ray-tracing algorithm regardless of the type of grid th at is
displayed. The examples given in this manual are of the plane-grid type. That is , the surface
of the Earth is treated as a flat surface. Likewise, the ionosphere is displayed as a flat
ionosphere, even though the algorithms still use a spherical Earth and a spheric al ionosphere.
This choice of the Options Menu lets you change the type of surface you see. In the
Plane Grid mode, you are given a flat surface. In the Spherical Grid mode, you a re given a
spherical surface and a spherical ionosphere to view the traced rays.
It must be stressed that even if you use the Plane Grid mode, all traced rays us e spherical
algorithms. This is why, when using the Plane Grid mode, traced rays are gradual ly bent upward
as the distance away from the transmitter increases.
3.3.15 Selecting Grid Distances and Height Scales
This option only applies to rays that are traced using the simple method.
Use this option to define what distances should be displayed on-screen when trac ing rays
through the ionosphere. All distances, whether ground distances or height distan ces, must be in
kilometers. For example, inputting a "Grid Distance" (or Ground distance) of 400 0 km and a
"Grid Height" of 400 km would, when tracing rays, display a grid 4000 km wide by 400 km
high.
It is important to realize that the grid-distance should be at least as large as the distance
between the transmitter and receiver. If the given grid distance is too small, t raced rays will
never reach the receiver but will be forced to stop when they reach the edge of the grid
boundaries. For example, if the distance between the transmitter and receiver is 7000 km and
you specify a grid distance of only 6500 km, the rays will hit the edge of the g rid at 6500 km
and will never reach the receiver 500 km beyond the end of the grid. To rectify this situation,
a grid distance of at least 7000 km should be used.
40
3.3.16 Accounting for Solar Flares
This option is only valid for rays traced using the simple method.
The existence of solar flares during the time when signals are propagating throu gh the
ionosphere can have a significant impact on the quality of signals. Solar flares can result in
strong absorption of signals in the lower ionosphere, particularly below the E l ayer.
PROPLAB lets you input the magnitude of a flare that may be influencing propagat ion
at the given date and time. The value you enter must be a valid flare-magnitude as was
described previously in the "Flare Rating System" (see section 2.2.3). For examp le, a magnitude
M6.3 flare would be entered as "M6.3". A magnitude X4.2 flare would be entered a s "X4.2".
PROPLAB will not recognize flares in the A, B, or C-class range, since flares of these types are
usually (if not always) incapable of producing any HF signal degradation.
Flares typically do not begin influencing propagation until they reach a class M 1.0 level.
Also, it is worth noting that flares do not have significant impacts on the dark -side of the Earth.
Only sunlit regions of the ionosphere are affected. As a general rule, the highe r the Sun is in the
sky, the stronger the ionospheric impact will be from the associated flare x-ray s.
Listen to radio stations WWV or WWVH for information regarding the state of the Sun
at 18 minutes past each hour on 2.5, 5, 10, 15, and 20 MHz. Flares capable of in fluencing
ionospheric radio communications exist when the recording states that solar acti vity was
"moderate", "high", or "very high". "Low" and "very low" levels of solar activit y denote 24-hour
periods of time where no flares of significance occurred. Radio stations WWV and WWVH
usually will not state the magnitude of observed flares. To find out this inform ation, you must
either call the duty forecaster at the Space Environment Services Center at 303- 497-3171 (collect
calls are not accepted), call the Solar Terrestrial Dispatch BBS at: 403-756-300 8. If you have
access to the electronic Internet network, you can obtain this information in ne ar-real-time
(maximum 3-hour real-time lag) by using the finger command: "finger [email protected] uleth.ca" or
by anonymously FTPing to the machine: "solar.uleth.ca" and grabbing the file "in dices.doc" from
the directory "pub/solar/Indices". A World Wide Web page will also become availa ble very
shortly (and may already be in operation). Contact: [email protected] to find out what
this address is.
3.3.17 Defining Polar Cap Absorption and Screen Saving Functions
The Polar Cap Absorption section of this option only applies to the simple ray-tracing
technique. The Screen Saving Functions apply to both the simple and the complex techniques.
The last choice of the Options menu gives you the ability to define the magnitud e (or
existence) of Polar Cap Absorption (or PCA) at the given date and time. PCA can have
devastating impacts on transpolar and transauroral circuits.
41
PCA measurements can be entered directly into PROPLAB in units of decibels (dB)
absorption. At the PCA input prompt, press ENTER if no absorption exists.
The existence of PCA can be determined by listening to radio stations WWV and WW VH
at 18 minutes past each hour on 2.5, 5, 10, 15, and 20 MHz. Although they don't report the
magnitude of PCA present, magnitude information can again be obtained from the s ame sources
as given previously in section 3.3.16. Refer to that section for more informatio n on the available
sources.
This choice of the Options menu also lets you alter the way PROPLAB saves graphi c
screen images to disk. Results of ray-tracing analysis or other graphical screen products can be
saved to disk by pressing the "G" or "P" keys. Pressing "G" causes PROPLAB to sa ve the
existing screen image to a GIF image file. Pressing "P" forces PROPLAB to save s creen images
to a PostScript-compatible file.
This option lets you alter the way screen images are saved. Screens can be saved to disk
in a full-color mode or a black-and-white mode. The full-color mode saves screen s to disk in
full-color, as they appear on your screen. The black-and-white mode saves screen images to disk
by first converting all non-black pixels to white and leaving black pixels black . The resulting
screen is black and white and may work better if being printed on monotone print ers.
3.3.18 Other Comprehensive Ray-Tracing Options
This option presents you with another full screen of modifiable ray-tracing para meters
that deal exclusively with the comprehensive ray-tracing technique. These option s are discussed
in the following group of subsections.
3.3.18.1 Ray-Tracing Model / Ray Type
This option lets you change the type of ray-tracing model that should be used wh en
performing comprehensive ray-tracings through the ionosphere. There are five models available.
Four of these five models are based on formulas and techniques developed by Appl eton and
Hartree and are hence known as the Appleton-Hartree models. The fifth model is t he Sen-Wyller
model. This model produces similar results but obtains them in a different manne r.
The first two Appleton-Hartree models include effects of the Earth's magnetic field (which
therefore allows both ordinary and extraordinary rays to be traced). However, th ey differ in that
the second model does not include the effects of electron collisions with neutral particles (a
significant phenomenon that is directly responsible for a producing most of the observed
ionospheric absorption).
The second and third models are similar to the first two, except neither of these two
42
models include effects of the Earth's magnetic field. Only ordinary rays can the refore be traced
using these two models. They differ in that the third model does include effects of electron
collisions with neutral particles whereas the fourth model does not.
The fifth model computes the refractive indices and associated gradients using a different
method than the Appleton-Hartree models, but produces similar results. It will l ikely only be of
interest to those with a knowledge of the differences between the Appleton-Hartr ee and SenWyller methods. This model does not include effects of the Earth's magnetic field but it does
include the effects of electron collisions with neutral particles.
The default and recommended model is the Appleton-Hartree formula that includes effects
of both the Earth's magnetic field and electron collisions with neutral particles (Model #1). This
model will produce the most accurate ray-tracings. It will be slower than the ot hers due to the
increased number of complex computations that must be performed, but the ability to trace
extraordinary rays as well as the added accuracy of the tracings is more importa nt than the
increased computation time.
3.3.18.2 Magnetic Field Model
This option lets you define the type of model to use to describe the Earth's mag netic field.
Several models are supported, but only one will likely be used for those with se rious applications.
The first choice of this suboption specifies that no magnetic field should be used. If this
option is selected, the type of ray-tracing model selected (see Section 3.3.18.1 ) should correspond
to a model that does not require a magnetic field.
The second choice is the default and recommended choice for those who are concer ned
about accuracy. This choice selects a standard dipole field model. This model cl osely resembles
the actual shape and intensity of the Earth's magnetic field and will produce th e best results for
most applications.
The third choice selects a model that assumes the DIP angle of the magnetic fiel d is
constant. The gyrofrequency of this model also increases as the cube of the dist ance. This
model will produce unrealistic results unless the user is familiar with appropriate applic ations for
this model.
The fourth choice selects a model that assumes a constant DIP angle and a constant
gyrofrequency, regardless of the location of the traced rays. Again, this model will produce
inaccurate and unrealistic results unless the user is familiar with the appropri ate applications for
this model.
We recommend using the second choice to select the Dipole Field Model . For general
applications, this will produce the best and most reliable results.
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3.3.18.3 Collision Frequency Model
This subsection defines the type of model that should be used to represent the e lectron
collision frequency through the Earth's atmosphere. It effectively defines the r ate with which
electrons collide with neutral particles in the Earth's atmosphere and ionospher e and is quite
important for accurate computations of ionospheric absorption values.
The first choice defines a model that uses two exponential terms. The second choice
defines a model that uses only one exponential term, while the third choice defi nes a model that
has a constant collision frequency model. The third choice will produce unrealistic results and
should only be used by those who have a knowledge of the applications through wh ich such a
model can be used.
By default, the model with
two exponential terms is used. The
difference between the first and
second models (supporting two and
one exponential terms respectively) is
almost negligible. Figure 3.0 shows
the collision frequency profile for
transmission frequencies that vary
from 100 KHz to 10 MHz. The lines
are defined from left to right as
follows: 10 MHz, 5 MHz, 1 MHz,
100 KHz. Altitude above the surface
of the Earth is indicated by the Figure 3.0: Collision Frequency Profiles using 2bottom scale (from 0 to 150 km). exponential terms for frequencies from 10 to 0.1 MHz.
Collision frequency is indicated by
the vertical scale. As can be seen, as the frequency of the ray is increased, th e effect of the
collision frequency decreases so that higher frequencies do not play as large a role in collisions
as low frequencies.
For those who are familiar with the exponential models of collision frequency, t he
exponential terms and reference heights which define the shape of these profiles can be adjusted
if necessary using other options in this Comprehensive Options menu.
3.3.18.4 Electron Density Model
This is the option that lets you choose which type of electron density model to use in
PROPLAB's comprehensive ray-tracings. The default is one of the three-dimensiona l models.
These models are discussed in detail in Section 3.3.4.2. Consult that section fo r more
information regarding the type of models to select.
44
3.3.18.5 Integration Method
PROPLAB PRO's comprehensive ray-tracing technique contains numerous complex
equations that must be integrated in order to ray-trace signals. These methods a re a little bit
older but produce reliable results. The first choice selects the Runge-Kutta int egration method
while the second choice selects the Adams-Moulton method. The Runge-Kutta method is slower
than the Adams-Moulton method, but produces a prodigious amount of information i f you have
instructed PROPLAB to save the ray-tracing results to the text file "RESULTS.OUT ". You can
choose to use either of these two methods, however the Adams-Moulton method tend s to be
slightly faster and perhaps only marginally more accurate than the Runge-Kutta m ethod. The
Adams-Moulton method is the default integration method.
3.3.18.6 Display Method
There are five available ways in which PROPLAB PRO displays ray-tracing results while
using the comprehensive ray-tracing technique. They are described below.
The first method does not graphically display any ray-tracing information on-scr een. It
instead simply computes the ray-tracing paths numerically and saves the results to the file
"RESULTS.OUT" if and only if you tell PROPLAB to create this file when you are answering
the prompts that define the elevation angles to use, etc. While PROPLAB is compu ting the raypaths, nothing will be displayed. You may therefore think PROPLAB has crashed yo ur computer
depending on the length of time required to complete the ray-tracings. This meth od is not
recommended as it does not graphically show you any ray-tracing results. But it might be useful
for those who are only interested in numerical results.
The second display method graphically displays rays traced through the ionospher e by
assuming you are looking at the ray cross-ways from the ground. That is, it appears as though
you are an observer looking at the traced rays perpendicularly. In this mode, yo u cannot discern
lateral deviations easily (if at all). But you can determine the altitude the ra ys travel. This mode
can also be simulated using the three-dimensional grid by appropriately rotating the display axes.
The third display method graphically displays rays traced through the ionosphere by
assuming you are looking directly down upon the rays from above. In this mode, you cannot
discern the altitude of the rays. This mode is useful if you are interested in t he extent to which
rays are being laterally deviated. However, the three-dimensional grid will also let you look
directly down upon the rays by rotating the grid appropriately.
The fourth display method is one of two available three-dimensional graphical modes.
This mode displays the progress of the traced rays using the rotatable three-dim ensional grid.
This lets you observe ray behavior from almost any conceivable viewing angle or perspective.
45
The fifth display method is the second available three-dimensional graphical mode. It is
similar to the last display mode described but differs in one important aspect. In this mode, ray
paths are displayed while they are being integrated . In the fourth display mode, ray-paths are
only displayed at specific points along the ray-path (ex. entering/exiting the i onosphere, progress
toward ray reflection, the location where the ray reverses direction, etc). The fourth display mode
might therefore trace a more course-looking ray-path. This fifth display method smooths out the
ray-path and displays as much ray-path information as possible. This is the reco mmended and
preferred three-dimensional display mode.
3.3.18.7 Transmitter / Receiver Height
PROPLAB PRO will let you vary the height of the transmitter or the receiver to v alues
from 0 kilometers to values as high as 1,000 kilometers. However, prudence must be exercised
when selecting transmitter or receiver heights. For example, selecting a transmi tter height that
is deeply within the ionosphere (for instance, near the F2 layer maximum of elec tron density
several hundred kilometers high) may force the transmitter to attempt to transmi t signals while
it is within the evanescent region. Transmissions and ray-tracings are not possi ble if the
transmitter is within such a region. Such conditions can occur when the transmit ter is within a
region of the ionosphere where the critical frequency (at the transmitter) is ne ar the transmitter
frequency.
By selecting wise transmitter heights, it may be possible to simulate the behavi or of
satellite transmissions. It is interesting to see how different the behavior of signals can be if the
height of the transmitter is only raised several tens of kilometers.
The receiver height can also be defined here. There are some known problems with
adjusting the receiver height above the recommended 0-kilometer level (which def ines the
transmitter as residing on the surface of the Earth). For example, PROPLAB PRO V ersion 2.0
sometimes will not properly end ray-tracing when the ray's closely approach the receiver location.
These problems do not appear if the receiver is left on the surface of the Earth . However, no
harm can be done if you play with different receiver heights. We will leave the choice of
whether or not to play with the receiver height up to you. Keep in mind, however , that adjusting
the receiver height may result in some ray tracings that are terminated prematur ely or incorrectly
(accuracy is not compromised).
3.3.18.8 Ray-Tracing Rate / Steps per hop
The comprehensive ray-tracing technique traces rays through the ionosphere by in tegrating
the rays through specified distances. The default distance is 1 kilometer and th is forms the basis
for the ray-tracing rate . Larger values force PROPLAB to trace rays through the ionosphere
using larger steps while smaller values force PROPLAB to use smaller steps.
46
The steps per hop prompt define how many times PROPLAB should attempt to solve the
ray-tracing problems before giving up. The default is 5,000 times, which should be enough for
most (if not all) cases. If this value is reduced too much, PROPLAB may give up trying to solve
ray-tracing problems before they are solved. If, during a ray-tracing session, y ou get an error
indicating that PROPLAB reached the iteration limit, increase this value in step s of approximately
500 to 1000. If this value is left at 5,000, PROPLAB should handle almost all in stances without
prematurely giving up.
3.3.18.9 Magnetic Pole Lat / Lon
This suboption lets you define the exact location of the Earth's northern geomagnetic pole.
It is only used if you are using a ray-tracing model that requires the Earth's m agnetic field as
input. Positive values represent northern latitudes and western longitudes. Nega tive values
represent southern latitudes and eastern longitudes. Results may differ consider ably from reality
if the southern magnetic pole or other geographical locations are used to repres ent the magnetic
pole.
3.3.18.10 Maximum / Minimum Ray-Tracing Step Length
This option lets you change the maximum and minimum allowed step lengths during
comprehensive ray-tracing. When PROPLAB is tracing through regions which are rel atively free
of refractive effects (as occurs, for example, when ray-tracing below the ionosp here), it is
permitted to increase the stepping length to the specified maximum value. When PROPLAB is
tracing rays through regions of the ionosphere where small increments in distanc e result in
substantial changes in refractive indices, PROPLAB is permitted to decrease the stepping length
to the specified minimum value in order to properly integrate the equations through the rapidly
changing regions of the ionosphere. The defaults of 10 km and 0.01 km for the ma ximum and
minimum step lengths will suffice under almost all circumstances. Decreasing the se values may
increase the accuracy of traced rays slightly but will slow down the computation s.
3.3.18.11 Left Latitude / Longitude of Display
PROPLAB PRO's comprehensive ray-tracing method requires
encompasses the geographical region where the signals are being traced.
by stating the latitude and longitude of the left-side corner coordinates
right-side corner coordinates of the ray-path. These two sets of corner
within which the rays are traced.
a viewing window that
This win dow is defined
of the ray-path and the
coordina tes form a box
PROPLAB automatically computes these corner coordinates for you, so you will sel dom
need to change them. However, if you ever do need to alter them, this option and the option
described in Section 3.3.18.12 (below) will let you do this.
47
We do not recommend you play with these values unless you know what you are doing.
Doing so haphazardly could cause PROPLAB to incorrectly draw the display grids o r even fail
to properly trace the rays. No harm can be done, however.
3.3.18.12 Right Latitude / Longitude of Display
This option defines the latitude and longitude of the right-side corner of the v iewing
window described in Section 3.3.18.11. Refer to that section for details. Positi ve values (for
both the left and right-side corner coordinates of the window) represent norther n latitudes and
western longitudes while negative values represent southern latitudes and easter n longitudes.
3.3.18.13 Grid Distance and Ticks
This option applies primarily to the three-dimensional display grids on which ra ys are
traced. It lets you specify the maximum grid distance to display on-screen. This distance must
be less than or equal to 20,000 kilometers. Since PROPLAB PRO's comprehensive ra y-tracing
engine will only trace short-paths and since the half-circumference of the Earth is 20,000
kilometers, this maximum permitted grid distance corresponds to the maximum trac eable shortpath distance. It should suffice for most applications.
For example, if the distance between the transmitter and receiver is 7,000 kilom eters, it
would be wise to specify a grid distance of at least 7,000 kilometers or more. I f you specify a
distance less than 7,000 kilometers, the receiver location will not be included on the grid.. It
would be wiser to specify distances that are several thousand kilometers greater than the
transmitter-receiver distance so that ray's which do not precisely reach the rec eiver distance will
continue to be traced until they hit the ground some distance beyond the receive r. It is generally
good practice to specify a distance approximately 4,000 kilometers beyond the re ceiver. This
corresponds to the approximate maximum one-hop limit.
The two remaining prompts let you define how PROPLAB should label the grids. The
first of these two prompts asks you to specify the distance between labelled tic ks on the distance
scale. For example, if the transmitter-receiver distance is 7,000 kilometers and you want
PROPLAB to display labelled tick marks (or lines) every 1,000 kilometers toward the receiver,
you would specify 1000 here. This lets you instantly estimate the ground locatio n and distance
the rays are from the transmitter during the ray-tracing phase .
The last prompt defines the lateral distance grid. Since traced three-dimensional rays can
deviate away from the great-circle path, the lateral distance grid gives you the ability to define
how large this lateral deviation grid should be.
The Figure beside this paragraph illustrates this further. The line drawn length wise down
the center of the grid in this Figure defines the great-circle distance between the transmitter and
48
receiver (which are located at the ends of
the "A" line). The distance grid runs along
the length of the A line. The lateral
deviation grid distance is the distance
represented by the "B" line. Rays which
deviate away from the great circle path will
begin to turn away from the A line and
begin crossing through a portion of the
distance represented by the B line. The last
prompt in this option defines how far
across the B line should span (in
kilometers).
By making the distance
smaller, you are able to discern smaller
lateral changes in the traced rays. By making the distance larger, you are able to discern larger
lateral deviations in traced rays. If the traced rays begin to laterally deviate beyond the given
lateral grid distance, you will need to increase the distance of the lateral gri d so that you can
better observe where the traced rays propagate.
The lateral grid distance you specify is centered across the A line above. For example,
by specifying a lateral grid distance of 500 kilometers, the B-line distance wil l be 500 kilometers,
spanning 250 kilometers on each side of the great-circle "A" line.
3.3.18.14 Distance between Ticks in Altitude
This option defines how many ticks (or lines) should be used to define the altit ude wall
of the three-dimensional grid. The default is 20 kilometers which provides reaso nably good
resolution. In other words, a line would be drawn on the altitude wall every 20 kilometers in
altitude.
The maximum height displayed on the altitude wall is determined by the HMax para meter
given below.
3.3.18.15 3-D Rotation Angles for the X / Y / and Z Axes
This suboption defines how you want to view the three-dimensional grid. It lets you
rotate the three dimensional grid in almost any conceivable fashion, effectively changing the
viewing perspective of the grid. This gives you the ability to view traced rays at almost any
angle desired.
The default rotation angles are -60, 0, and 20 degrees for the X, Y, and Z axes
respectively. These rotation angles provide a good view of the traced rays (both in altitude,
distance, and lateral deviation).
49
Note that PROPLAB will accept almost any set of angles here. However, some exoti c
angles may cause PROPLAB to improperly draw grid borders, labels or other things . Even so,
no harm can be done (it may just be more difficult to see), so feel free to play with this section
until you find values that are aesthetically pleasing.
3.3.18.16 Zoom Factors and X / Y Axis Offsets
PROPLAB PRO has the ability to display three-dimensional grids that are zoomed i n or
out. The X and Y axis offsets permit zooming centered on any location of the thr ee-dimensional
grid.
Zoom factors must be specified in percentages, where zero percent represents an
unzoomed screen. A zoom factor of 100 percent will zoom into the three-dimensional grid
(centered on the center of your monitors screen) by a factor of 2 times the norm al. Similarly,
a zoom factor of -50 percent will cause PROPLAB to zoom out by 50 percent (thereby making
the three-dimensional grid half the size on the screen).
The X and Y axis offsets are relative to the middle of your monitors screen, not the
middle of the three-dimensional grid. They are also both stated in percentages o f screen widths
and heights.
The X-axis offset defines the center location of the X-axis of your screen. The default
value is 0.00 percent, which corresponds to the 320th horizontal pixel on VGA di splays. A value
of +30.0 percent corresponds to a location 30% to the left of the 320th horizontal pixel while a
value of -30.0 percent corresponds to a location 30% to the right of the middle of your screen.
The Y-axis offset is defined similarly. The default value of 0.00 percent corres ponds to
the 240th vertical pixel on VGA displays. A value of +30.0 percent corresponds t o a location
that is 30% above the middle of your screen while a value of -30.0 percent refers to a location
that is 30% below the middle of your screen.
By adjusting these variables, it is possible to zoom in to features of traced ra ys that might
be difficult to see under normal circumstances.
3.3.18.17 HMax (and Altitude Grid) / Ym / and foF2 Layer Shaping Factors
This option will likely only be used by those who have a firm knowledge of the
mathematical representations of ionospheric electron density profiles. These opt ions are used
primarily by the Quasi-Parabolic and Alpha-Chapman electron density models and m ust be
adjusted to the appropriate values prior to performing any raytracing. The two-dimensional
electron density models (CCIR and URSI) require the foF2 (critical frequency of the F2 layer)
parameter only. The other two parameters (HMax and Ym) are not used in the URSI or CCIR
two-dimensional electron density models.
50
The HMax parameter refers to the altitude above the surface of the Earth where t he
electron density reaches a maximum (usually in the F2 layer). This parameter is also used to
adjust the height of the altitude grid "wall" on three-dimensional displays. For example, to
display a three-dimensional grid up to an altitude of 400 km, enter 400 at this prompt. The Ym
parameter defines the thickness of the ionospheric layer being modelled. And the foF2 parameter
defines the critical frequency of the ionosphere at the HMax altitude. The foF2 determines the
maximum electron density of the layer through the formula: 1.24E+10 x foF2.
These parameters should apply to the midpoint of the ray paths in order to produce
accurate single-hop ray-tracings.
If you are using a three-dimensional electron density model, these parameters wi ll not be
used. For novices in ionospheric radio propagation, using a three-dimensional mo del is highly
recommended.
3.3.18.18 Ground Gyrofrequency at the Equator
The gyrofrequency refers to the number of times charged particles such as electrons and
ions spiral around the Earth's magnetic field lines per second. The rate with wh ich these particles
spin around the magnetic field lines is related to the strength of the Earth's m agnetic field. The
gyrofrequency at the ground and on the equator is used by PROPLAB as a reference in some of
its ray-tracing operations. Altering the given value should only be done by thos e who know what
the implications are of doing so. In most (if not all) instances, this option wi ll not need to be
used.
3.3.18.19 Electron Collision Frequency and Profile Shaping Parameters
Electron collision frequency profiles are used by PROPLAB to model the frequency with
which electrons collide with neutral particles in the atmosphere. This phenomeno n is critical for
determining ionospheric absorption of radio signals that travel through the iono sphere.
The 19th and 20th suboptions of the Comprehensive Options menu define the electr on
collision frequency model parameters that determine the overall shape of the ele ctron collision
frequency models used in PROPLAB. We recommend these values are not touched unle ss you
are familiar with electron collision frequency profiles and the models used to d erive them.
The equations used to derive the electron collision frequencies are shown below:
51
This equation gives the electron collision frequency for one exponential term and therefore
corresponds to the collision frequency model containing only one exponential ter m. In the above
equation, N corresponds to the collision frequency at the height corresponding to RefHeight. The
frequency of the signal being broadcast into the ionosphere is defined by Xmitfreq and is given
in MHz (the multiplication by 10 6 converts MHz to Hz). The variable A defines the value of the
exponential term that determines the shape of the profile at the altitude RefHeight.
The equations used to derive the electron collision frequencies with two exponential terms
follows below:
In this equation, N1 corresponds to the collision frequency at the height corresponding to
RefHeight1 and A1 is the exponential value that gives this section of the model its shape at
RefHeight1. N2 is the collision frequency at the height corresponding to RefHeight2 and A2 is
the exponential value that gives the model its shape at the height RefHeight2. And as in the
previous equation, Xmitfreq is the frequency of the signal being transmitted through the
atmosphere in MHz.
With this information in-hand, the Comprehensive Option menu choices (#19 and #2 0)
can be appropriately changed to yield the collision frequency profiles you desir e.
3.3.18.20 Three-Dimensional Data (Important!)
Option #21 of the Comprehensive Options menu is a VERY Important section that must
be changed every time you change the transmitter/receiver locations or ionospher ic profiles.
Failing to do so will result in inaccurate ray-tracings!
This is the section where you are asked all of the critical questions which dete rmine how
PROPLAB builds the ionospheric profiles necessary to support three-dimensional c omprehensive
ray-tracing.
Before proceeding further, make sure you have read and understood Section 3.4.1.3
(Understanding the Generation of Ionospheric Profiles). That section will teach you everything
you need to know about how PROPLAB generates ionospheric profiles for three-dime nsional raytracing so you will be prepared to properly respond to these important prompts.
52
PROPLAB first shows you the current 3-D data settings. This is followed by the b earing
from the transmitter to the receiver as well as the computed great-circle distan ce between these
two points. Check to make sure it is all correct. If it is not, use Main Menu Op tion #8 (or #3)
to change the geographical locations of the transmitter and receiver to the corr ect latitudes and
longitudes. Then re-enter this section to specify the three-dimensional data.
PROPLAB first asks you to specify how many degrees adjacent (perpendicular) to t he
bearing (of the great-circle path) ionospheric profiles should be constructed. F or example, if you
specify 10 degrees here, PROPLAB will construct ionosphere profiles spanning 10- degrees on
BOTH sides of the main great-circle bearing. It will therefore construct profiles covering a total
azimuthal span of 20 degrees (10-degrees per side). A value of 1 degree will cau se PROPLAB
to construct profiles only one degree on either side of the main bearing. If the main bearing was
therefore 315 degrees from the transmitter to the receiver, PROPLAB would constr uct ionospheric
profiles at bearings of 314, 315 and 316 degrees (one degree on each side of the main bearing).
PROPLAB next asks you how many profiles you want to build along the bearing rang e.
The bearing range refers to the total azimuthal span for which profiles will be constructed. In
the first example above, the bearing range would have been 20 degrees (10-degree s per side).
In the second example, the total bearing range would have been 2 degrees (1-degr ee per side).
This prompt is therefore essentially asking you what the stepping rate should be between
successive sets of azimuthal ionospheric profiles. The stepping rate can be comp uted by dividing
the bearing range by the number of profiles you want to build along the bearing range. For
example, if the bearing range is 20 degrees and you want to build 50 sets of pro files along that
range, PROPLAB would use a stepping rate of (20 / 50) 0.4 degrees. Assuming the main bearing
is 315 degrees, the first set of profiles would be built along the bearing (315 - 10) 305 degrees.
The second set of profiles would be stepped by 0.4 degrees and would therefore b e built along
the bearing 305.4 degrees. The third set of profiles would be built along the be aring 305.8
degrees, etc - in the end resulting in about 50 sets of ionospheric profiles cov ering the bearing
range from 305 to (315 + 10) 325 degrees in 0.4 degree increments. This prompt i s important
for preventing data gaps in ionospheric profiles.
The next prompt posed by PROPLAB asks you to specify the distance (in kilometers )
behind the receiver to begin computing the various sets of ionospheric profiles. In mo st
instances, a value of 0 kilometers will be specified here, indicating that the f irst profile generated
along each bearing should be directly above the transmitter.
The following prompt asks you to specify the distance ahead of the transmitter (in
kilometers) to end ionospheric profiles. The total distance specified here (defi ned as the distance
ahead of the transmitter minus the distance behind the transmitter) determines t he length of one
segment as described in Section 3.4.1.3.
PROPLAB next asks you to specify the number of individual ionospheric profiles y ou
want to build along the total distance of the specified segment . You can instruct PROPLAB to
build up to 46 individual ionospheric profiles along the length of a segment. It therefore defines
53
the resolution of the ionospheric profiles used in three-dimensional ray-tracing . For example, if
the total distance of a segment was 8,000 kilometers and you state that you want to build 20
profiles along this distance, PROPLAB will generate one ionospheric profile ever y (8000 / 20)
400 kilometers. The resolution can be increased by increasing the number of prof iles from 20
to 46. This reduces the distance between individual successive ionospheric profi les from 400
kilometers to 174 kilometers.
The last prompt posed by PROPLAB asks you how many segments you want to build
ionospheric profiles for along each bearing. In the above example, if we specifi ed 2 segments
(each of which is 8,000 kilometers in distance), we would be able to trace rays along any of our
bearings out to a distance of (8000 x 2) 16,000 kilometers.
After answering these prompts, PROPLAB is ready to begin building ionospheric pr ofiles.
This is accomplished by actually instructing PROPLAB to begin a comprehensive ra y-tracing
session (use Main Menu Option #1).
3.4 PROPLAB's Main Menu Functions
The Main Menu of PROPLAB gives you access to all of the functions of PROPLAB and
is responsible for loading and executing the appropriate subprograms when reques ted. It consists
of nine options which are described below.
3.4.1 Ray Tracing Signals
PROPLAB is very flexible in the way it permits signals to be traced through the
ionosphere. Before ray tracing can be accomplished, it is important to setup the appropriate
parameters in the Options Menu (see Section 3.3) so that PROPLAB knows all about the signal
you are transmitting from one point to another.
As has been noted in previous sections of this manual, there are two main ray-tr acing
methods that are available: a simple technique and a comprehensive (or complex ) technique. The
first option of the Main Menu lets you choose which type of ray-tracing techniqu e you want to
use. Use the simple method if you are more concerned about a quick analysis of t he way signals
are reflected from the ionosphere. Use the comprehensive method if you need accu rately raytraced signals that show you more precisely where signals are going. Use a three -dimensional
model of the comprehensive method to see where signals go in three dimensions.
3.4.1.1 Ray Tracing Signals using the Simple Ray-Tracing Technique
There are three different methods you can use to trace signals through the ionos phere.
The first is by holding the frequency of the signal and the time of the transmis sion constant, and
54
sweeping the elevation angle of the transmission. The second is by holding the e levation angle
and time of transmission constant and sweeping the frequency of the signal. And the third is by
holding the elevation angle and the frequency of the signal constant and sweepin g the time of
the transmission. By "sweep", we mean to increase the value from a lower value t o a higher
value in user-specified steps or increments.
Each of these three methods provide valuable and different results. For example, most
radio transmitter antennas are capable of transmitting in specific or preferred directions. That is,
their radiation patterns are usually higher in certain directions. These are cal led directional
antennas. Omni-directional antennas are associated with radiation patterns that are essentially
equal in all directions. That is, the power transmitted away from the antenna is equal in all
directions. By selecting ray tracing by sweeping elevation angles, you can essen tially analyze
the performance of specific transmitters by sweeping transmission elevation angl es in accordance
with the radiation pattern of the antenna. To clarify, let's assume that you hav e an antenna that
is most efficient in transmitting between 4 and 12 degrees of elevation above th e horizontal.
That is, most of the power is radiated in a field that lies between 4 and 12 deg rees in elevation.
Now you want to determine propagation quality of a signal being propagated from your location
to a distant region 3,000 kilometers away, but you are uncertain whether your tr ansmitter will be
able to send a signal that distance. Using this first function to sweep elevatio n angles, you can
set up PROPLAB to begin tracing rays through the ionosphere beginning at an elev ation angle
of 4 degrees and ending when the elevation angle reaches 12 degrees. The step ra te you choose
to use is entirely up to you. If you want PROPLAB to trace 3 rays on-screen betw een this range,
you would select a step rate of 4 degrees of elevation per trace. For 16 traced rays (and hence,
greater resolution in the results), you would select a step rate of 0.5 degrees of elevation per
traced ray.
The usefulness of sweeping elevation angles is not restricted to the above examp le. There
are many other useful ways to use this function. For example, if you need to kno w exactly what
distance your signal strength is a maximum on a given frequency, you would selec t this option
to sweep elevation angles. Since signal strength is proportional to the concentr ation of rays that
strike the ground per unit area, you would look for a pattern similar to Figure 2.5, where the rays
become concentrated. The area where the rays are most concentrated is the locati on (and
distance) of maximum signal strength.
Another way to use this function is to determine what angle of elevation to use for signals
to reach a specific distant location. Most propagation programs give you a singl e transmission
angle of elevation for signals to reach destinations. Unfortunately (as you will discover while
using PROPLAB), those angles of elevation can often be significantly in error be cause the
algorithms used are empirical in nature and attempt to lump together all ray pat hs. In other
words, those programs do not consider individual ray paths in the ionosphere and as a result must
estimate elevation angles. The method employed by PROPLAB is one of the most acc urate
methods available and should yield good results under most conditions. Because P ROPLAB
traces each ray individually through a dynamic ionosphere, the angle of elevatio n required to
reach a specific distant destination can be accurately pinned down. Simply sweep a range of
55
elevation angles and look for rays that strike close to the desired destination.
PROPLAB uses the arrow at the bottom of the screen (in the distance scale as has been
shown in previous Figures), along with a vertical dotted green-colored line, to mark the exact
location of the destination point. It is therefore easy to determine the proximi ty of traced rays
to the destination by simply comparing the location of the rays with the arrow o r green dotted
line.
Sweeping frequencies is as useful as sweeping elevation angles. Sweeping frequen cies
can tell you a great deal about how the ionosphere responds to different signals . For example,
by sweeping frequencies, you can determine what frequency to use to penetrate th rough dense
layers of sporadic-E, or through other ionospheric layers. Since long-distance c ommunications
occurs best through F2-layer reflections, sweeping frequencies can help you dete rmine what
frequencies to use to penetrate through the D, E, and F1 layers for reflection f rom the F2 layer.
During the day, when ionization of the D, E, and F1 layers is highest, this soft ware feature can
significantly help you isolate optimum frequencies for specific paths.
Sweeping time from hour to hour, or minute to minute lets you analyze the behavi our of
the ionosphere over time and how it responds to the signals you transmit. This i s a very useful
feature for determining what times of the day certain frequencies open up for lo ng-distance
communications, or for observing what happens (for example) at sunrise or sunset and how signal
propagation radically changes during these periods of time.
The fourth option available in this Ray-Tracing Menu (Generate Oblique Sounder
Ionogram) is a powerful function that requires an entire section within this man ual to adequately
describe. Refer to Section 8 for details regarding this function.
3.4.1.2 Ray Tracing Signals using the Comprehensive Ray-Tracing Technique
The menu associated with the comprehensive ray-tracing technique lets you trace rays
through the ionosphere by sweeping elevation angles, frequencies, azimuths or any (or all) of
these three together.
The prompts associated with the elevation and frequency sweep selections are sim ilar to
those for the simple ray-tracing method and need no further explanation here. Th e option to
permit tracing rays by sweeping azimuths is new to PROPLAB PRO Version 2.0, but is selfexplanatory. Enter in the starting and ending azimuths (clockwise from true nort h - east is 90
degrees azimuth) you want to transmit toward in degrees. Also enter in the rate with which you
want to step the azimuth from the starting to the ending azimuth (in degrees).
PROPLAB PRO Version 2.0 prompts for several additional items that are not presen t in
the simple technique (and in fact have not ever been present in prior releases o f PROPLAB).
These prompts are described below.
56
After selecting which component to sweep (elevation angles, frequencies or azimu ths), you
are asked to input the "azimuth of the transmitting antenna" in degrees clockwis e from true north.
This is the azimuth of the main radiation lobe of the transmitting antenna. For instance, if your
antenna has a radiation pattern that radiates most of the transmitted power dire ctly toward the
east, you would specify an azimuth of 90 degrees. If your antenna is rotatable, specify the
current azimuth of the antenna's main radiation lobe. This is an important parameter that must
not be overlooked. PROPLAB PRO uses this information to compute the field streng th of the
signal. Entering the proper antenna azimuth as well as the proper type of antenn a is necessary
if PROPLAB is to produce reliable results.
The second prompt asks you if you want to "Store text results in the file 'resul ts.out' ?"
When using the comprehensive ray-tracing technique, PROPLAB PRO will optionally create a
text file and write various bits of information to that file while rays are bein g traced through the
ionosphere. For example, whenever a ray reaches an apogee or perigee (maximum he ight or
minimum height respectively), is reflected by the ground, penetrates the ionosph ere, or reaches
the receiver, PROPLAB writes information to this file. Information written inclu des such
parameters as the ground range, the latitude/longitude of the ray, the polarizat ion of the ray,
ionospheric absorption encountered, geometrical path distance, phase path, group path and ray
deviations and bearings, etc. This information can be used to gather more detail ed data regarding
a particular traced ray. If you want this type of information stored, select "y" es at this prompt.
Be aware that the size of this file can become quite large fairly quickly (particularly if the
Runge-Kutta integration technique is used) if many rays are traced with this opt ion enabled.
For each comprehensively traced ray, PROPLAB writes specific information to a bi nary
file in the PROPLAB directory. This information can then be later read and analy zed by
PROPLAB functions which will (for example) plot the locations of traced rays on global maps,
produce contoured field-strength maps, etc. Since you cannot stop PROPLAB from w riting this
information, you must only decide whether you want to "A"ppend the results to th e file or
"C"reate an entirely new file (effectively truncating any existing data and rewr iting the file from
scratch). If you choose to "C"reate the ray-database file, PROPLAB will erase an y contents that
may already exist in that file. So be careful. If you recently performed a large ray-tracing
session and do not want to lose that information, but you do want to trace a different set of rays
along a different path, then go to the DOS prompt and rename the database file
("RAYOUT.DAT") to something else before responding to this prompt. To abort this prompt
without doing anything, press the ESCape key. For most applications, you will pr obably "C"reate
a new database file each time you trace rays through the ionosphere. In cases wh ere you may
be performing several ray-tracing sessions that are all related (that is, they h ave the same or
similar paths, transmitter/receiver locations, frequencies, etc), you may want t o "A"ppend the
results to the existing database file so that the database of information is sup plemented with the
new results.
After inputting the starting, ending, and stepping values, you are asked whether or not you
want to "Use the existing electron density profiles ?" This is a very important question that you
must answer properly. But before you can give a qualified answer, you must bette r understand
57
how and why PROPLAB PRO uses electron density profiles. The next section (Sectio n 3.4.1.3)
discusses this in detail. Please read that section next before proceeding. The r est of this section
should then be easily understood.
If you choose to use the existing electron density profiles, PROPLAB will immedi ately
load up the ray-tracing engine and begin ray-tracing the signals through the ion osphere using the
existing set of ionospheric profiles. If you choose not to use the existing electron density
profiles, PROPLAB asks you whether or not to delete the existing profiles from t he PROFDATA
subdirectory before building the new profiles. If you need to increase the resol ution of the
profiles (ex. decrease the steps between successive profile azimuths), select "n "o at this prompt
so PROPLAB will not delete the existing profiles. By specifying "n"o, PROPLAB as ks you
whether or not it should overwrite existing profiles if it encounters any. If yo u instruct
PROPLAB not to overwrite profiles, the speed of the profile-generating phase will increase since
any existing profiles that match those that are requesting to be built will be s kipped (not
overwritten). If you want to make sure that all of the profiles are fresh and in -tact, instruct
PROPLAB to overwrite any profiles that already exist.
Please note that the above prompts apply mostly to three-dimensional ionospheric models.
Two-dimensional models are not quite as demanding, as only a single profile file is built (by the
name of "IRIPROF.DAT" in the main PROPLAB directory). The prompt asking whether or not
to delete existing profiles does not apply when two-dimensional models are used and should be
answered with a "N"o (meaning you don't want to delete any existing 3-D profiles).
Following these prompts, PROPLAB begins to automatically compile the required pr ofiles
in the PROFDATA subdirectory (for 3D profiles or in the main PROPLAB directory f or 2D
profiles). After it finishes building the profiles, it automatically loads the r ay-tracing engine and
begins comprehensively tracing the signals through the ionosphere.
3.4.1.3 Understanding the Generation of Ionospheric Profiles
The comprehensive ray-tracing technique differs from the simple ray-tracing tech nique in
that it cannot compute the characteristics of the ionosphere "on the fly" as the simple method can.
The reason has to do with memory constraints. The comprehensive ray-tracing engi ne is an
exceptionally complex and large software program. In order to fit it all into me mory, some
desirable features had to be removed such as the ability to compute on-the-fly i onospheric
profiles. We could have used overlays to add this ability, but the use of overla ys would have
dramatically decreased the performance and speed of the ray-tracing engine. Futu re releases of
PROPLAB may include an overlaid version that supports on-the-fly profile generat ion. For the
current version of PROPLAB, the ionospheric profiles are not generated on-the-fl y but must still
be provided in some way so that PROPLAB can in fact compute profiles for any distant point
along a given azimuth. The method described here is the simplest and most rapid method we
could devise that does not sacrifice accuracy.
58
The following discussion assumes a three-dimensional ray-tracing is being perfor med.
In a realistic three-dimensional ionosphere, the character of the ionosphere is constantly
changing. Electron densities (which are major players in the refraction of radio waves) vary
widely from place to place. They are high near the equators, low near the poles, highest near
the magnetic equator in the afternoon, lowest in the high latitudes near dawn, a nd are constantly
changing intensity. These profiles, however, are extremely important if realisti c rays are to be
traced through such a dynamic ionosphere.
To
generate
these profiles,
PROPLAB PRO splits
up a specific path
(along a particular
azimuth) into a userdefined number of
segments (see Figure
3.1). Within each of
these segments,
PROPLAB computes
a user-defined number
of ionospheric
profiles. Each of the
computed
profiles
Figure 3.1: How PROPLAB Segments Paths and Computes Profiles . contains several other
profiles immediately
adjacent to the main
bearing of the signal. Figure 3.1 shows this in greater detail. The top part of this figure shows
the entire path, divided into 3 segments. The inset shows a part of Segment #1 i n greater detail.
In the inset, the solid line represents the main bearing (the great-circle path) of the signal. In
order to compute the spatial gradients of electron density along this main beari ng, it is necessary
to know the ionospheric characteristics immediately adjacent to this main bearin g. So PROPLAB
computes ionospheric profiles along successive sections of each segment as shown by the P-lines
in Figure 3.1. Along each of these P-lines (adjacent to the main bearing), PROPL AB computes
profiles a short distance from the main bearing, as indicated by the small squar es along the P1
and P10 lines. Although it is not shown, profiles are computed in similar locati ons along each
P-line.
So now PROPLAB knows the ionospheric profiles along the main bearing and it also
knows the characteristics of the ionosphere at small distances away from the mai n bearing. This
is all of the information that is necessary for signals to be traced in three di mensions, since it
allows us to compute all of the required spatial gradients of electron density a long the path the
signal travels (provided it does not deviate from the given azimuth).
59
The ionospheric profiles produced by PROPLAB tend to span lateral distances of u p to
about several hundred kilometers away from the main bearing. That is, the distan ce between the
outermost squares in Figure 3.1 will vary but typically span approximately sever al hundred
kilometers, depending on the geometry of the path. This is important to realize since it will help
you understand whether or not you might need to build other ionospheric profiles parallel to the
main bearing.
Signals that travel through the ionosphere frequently travel paths that do not s trictly
correspond to the anticipated great-circle path. Ionospheric tilts, effects of t he Earth's magnetic
field, and other anomalies can cause rays to deviate from the great-circle path. These deviations
must be taken into consideration when generating ionospheric profiles. This is i mportant because
if PROPLAB cannot find an ionospheric profile for a specific part of the ray pat h, it will produce
a warning indicating that the "ray went out of the grid bounds". In other words, PROPLAB is
unable to determine the necessary ionospheric parameters to accurately ray-trace signals through
the ionosphere. This can result in inaccuracies in the traced rays.
To overcome this difficulty, the Comprehensive Options Menu (Main Menu #8, Subop tion
#18) contains an option (option #21) that lets you set up exactly how PROPLAB sh ould create
the ionospheric profiles. PROPLAB lets you develop ionospheric profiles over a r ange of
bearings that are centered on the main great-circle bearing to the receiver. For example, if the
bearing from the transmitter to the receiver is 100 degrees, you can use this op tion to develop
ionospheric profiles that might span, for example, a 5-degree bearing spread on either side of the
great-circle bearing. PROPLAB would then create ionospheric profiles spanning fr om 95 to 105
degrees. Another prompt presented within this option determines how many profile s to build
along the bearing range. In other words, you are asked to type how many ionosphe ric profiles
should be built between the 95 to 105 degree bearing range. The more profiles yo u build along
the bearing range, the less likely PROPLAB is to trace a ray through a location where the
ionospheric characteristics cannot be determined.
To help explain why PROPLAB might not be able to find an appropriate profile, re fer to
Figure 3.2. The two X's shown in this figure correspond to the transmitter and r eceiver locations.
The great-circle path between these two points is represented by the imaginary s traight line
between the two X's. In this figure, we have generated eight ionospheric profile s that describe
the characteristics of the ionosphere between the transmitter and receiver at ei ght different
azimuths indicated by the eight shaded regions in Figure 3.2. When a sufficient number of
profiles are generated along the bearing range, the profiles begin to overlap so that there are no
regions between the transmitter and receiver that are devoid of ionospheric info rmation. In other
words, if the number of profiles is sufficient, PROPLAB will know everything it needs regardless
of where signals may travel between the two points. If in Figure 3.2, the ray to ok a path that
travelled above the right-side X, the ionospheric profiles would be able to desc ribe the
characteristics of the ionosphere consistently (there are no data gaps). However , if an insufficient
number of profiles are generated, PROPLAB may begin to see gaps where the ionosp heric
profiles do not overlap. If traced rays encounter any regions where there are ga ps (as the one
shown in Figure 3.2), it will not be able to accurately compute the ionospheric characteristics.
60
This will degrade the
accuracy (often very
seriously) of the
traced rays.
It is
therefore important
that you specify a
large enough number
of profiles so that
gaps are eliminated.
Y o u c a n
calculate how closely
spaced the various
ionospheric profiles
are (in bearing) to one
another by dividing Figure 3.2: Gaps in Ionospheric Profiles (see text)
the bearing range by
the number of profiles
you are generating. For example, in the example above, we wanted to generate pro files covering
a 5 degree spread on either side of the great-circle bearing. The total bearing spread is therefore
10 degrees (105 degrees - 95 degrees = 10 degree spread). By telling PROPLAB to generate 10
ionospheric profiles over this bearing range, PROPLAB will generate profiles eve ry 1.0 degrees
in bearing (10 degree spread / 10 profiles = 1.0 degree). PROPLAB will then gene rate the first
profile at a bearing of 95 degrees, the second profile at 96 degrees, etc, until the bearing exceeds
105 degrees. You can increase the resolution of the profiles (that is, make them overlap more
to reduce or eliminate gaps in data) by increasing the number of profiles. For e xample, by
specifying 30 profiles instead of only 10, you effectively instruct PROPLAB to p roduce
ionospheric profiles every 0.3333 degrees in bearing (10 degrees / 30 profiles = 0.3333 degrees
per profile). PROPLAB would then create the first profile at 95 degrees, the sec ond profile at
95.3333 degrees, the third profile at 95.6666 degrees, etc, until the bearing in creased beyond 105
degrees. Hence, the lower the stepping rate, the higher the resolution, the grea ter the overlap in
profiles, and the less chance there will be for data gaps.
The smallest stepping rate allowed by PROPLAB is a stepping rate of 0.1 degrees in
bearing. Even for very long-distance paths near the 20,000 kilometer limit of PR OPLAB's
comprehensive ray-tracing engine, this stepping rate usually suffices. However, be aware that
as the distance between the transmitter and the receiver increases (or rather, a s the ray moves
farther and farther away from the transmitter), the probability of the ray encou ntering data gaps
increases. This is because as the distance increases, the amount each successive profile overlaps
the preceding one decreases.
The above discussion illustrates how PROPLAB is able to compute ionospheric
parameters for rays that deviate away from the great-circle path. However, we st ill do not know
how PROPLAB computes the ionospheric profiles along each of these different bearings. We
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have, until now, assumed that PROPLAB simply knows the ionospheric characteristi cs at every
possible point in distance between the transmitter and receiver on specific bear ings adjacent to
the great-circle bearing. This is essentially true because PROPLAB performs inte rpolation to
make it true. But in reality, the interpolation performed introduces possible ar eas where traced
rays may begin to deviate from reality. The following discussion explains why.
When setting up the parameters (in suboption #21 of the Comprehensive Options me nu),
PROPLAB prompts for the distance in kilometers along each bearing to compute the ionospheric
profiles. This is followed by a prompt asking how many individual ionospheric "s amples" should
be taken along the specified distance (up to a limit of 46). For example, if on each desired
bearing within the bearing range, you want PROPLAB to generate ionospheric profi les along a
15,000 kilometer path, you can instruct PROPLAB to generate up to 46 ionospheric profiles
along that path. That amounts to one profile every 326 kilometers (15000 / 46 = 326). This
means that each successive ionospheric profile is separated by 326 kilometers. I n order to
prevent gaps in data from appearing, PROPLAB must perform interpolation when rays are inbetween ionospheric profiles (as would occur if a ray was part-way between profi les that were
spaced 326 kilometers apart). This interpolation process is a source for possibl e inaccuracies in
traced rays. The level of inaccuracy is proportional to the distance separating ionospheric
profiles. In other words, the closer the spacing in distance is between successi ve ionospheric
profiles, the more accurate the ray tracing will be. A spacing of 326 kilometers is a fairly hefty
distance. The character of the ionosphere may change appreciably within this dis tance.
Therefore, it would be wise to decrease the spacing between ionospheric profiles so that we
obtain a more realistic sampling of the ionospheric characteristics. In this exa mple, we are
unable to decrease the distance between ionospheric profiles because we are alre ady using the
maximum allowed number of profiles (46). We are in luck, however, because PROPLA B will
let you split up the 15,000 kilometer path into up to 9 segments (as illustrated in Figure 3.1).
It will then let you generate up to 46 ionospheric profiles within each segment ! This gives you
the ability to sharply increase the number of profiles generated over the 15,000 kilometer path
from 46 to as much as 414 (46 profiles x 9 segments).
So let's see what happens if we use segmentation in our example. At the prompt a sking
for the distance along each bearing, let's specify a distance of 7,500 kilometer s (we're splitting
the 15,000 kilometer path into two segments of 7,500 kilometers each). When prompted for the
number of profiles to build along the 7,500 kilometer path, we will specify the maximum allowed
of 46. The last prompt presented asks you how many segments should be built. By specifying
a value of 2, PROPLAB will build a total of two segments along each bearing spec ified, spanning
a total distance of (2 segments x 7,500 kilometers) 15,000 kilometers. However , notice that
within each segment we are creating 46 ionospheric profiles, thus decreasing the distance between
ionospheric profiles from 326 kilometers to 163 kilometers (half the distance!). The resolution
has therefore increased by a factor of two! By specifying a value of 3 segments (instead of two),
PROPLAB would build three segments, each 7,500 kilometers in distance. Rays could therefore
theoretically be traced out to a distance of (7,500 kilometers x 3 segments) 22, 500 kilometers.
However, in reality, this distance would be limited to 20,000 kilometers because PROPLAB's
comprehensive ray-tracing engine will not trace beyond this distance.
62
By splitting up our 15,000 kilometer path into 9 segments containing 46 profiles each, we
decrease the spacing between ionospheric profiles from 163 kilometers (for 2 seg ments) to 36
kilometers (15,000 km / 9 segments / 46 profiles-per-segment). This is the best PROPLAB can
do and is far better than we probably really need because in most cases, ionosph eric
characteristics do not change appreciably over distances as small as 36 kilomete rs. Hence,
interpolation will not introduce any appreciable inaccuracies in the traced rays .
PROPLAB saves each segment of ionospheric profiles to a separate disk file within the
PROFDATA subdirectory that is created when you install PROPLAB. If you instruct PROPLAB
to build 9 segments, it will save 9 separate files containing all of the ionosph eric profiles for
those segments.
PROPLAB saves one file for every step in the bearing (or azimuth) that is used, as well.
For instance, in our example where we built ionospheric profiles spanning a 10-d egree range at
steps of 1 degree each, PROPLAB would save 10 separate files to the PROFDATA sub directory
(one for the 95 degree bearing, another for the 96 degree bearing and so on unti l the 105th degree
bearing was saved). By using a stepping rate of 0.1 degrees per bearing, the num ber of saved
files increases to 100 (10 degree range / 0.1 degrees per bearing).
The amount of disk space consumed increases dramatically if you are not careful in your
selection of parameters. The more profiles you build along each segment (up to a maximum of
46 profiles per segment), the greater the disk space will be. One profile per se gment produces
a small file size (less than about 10K bytes). Specifying 46 profiles per segmen t, however,
requires nearly 152K bytes of disk space per file ! Therefore, in the above examples, saving 9
segments containing 46 profiles across a 10-degree bearing range using 0.1 degre e bearing steps
could result in a profile database being created that approaches 136.8 megabytes ([10 degree span
/ 0.1 degree stepping rate] x 9 segments x 152K bytes per segment)! Systems with large harddrives could conceivably handle this, but most likely this level of resolution i s overkill unless you
require highly accurate results with essentially zero inaccuracies. It would be far better to reduce
the number of segments to 2 or 3. In most cases, a 0.1 degree bearing stepping r ate is also
overkill, particularly on shorter distances less than about 10,000 kilometers. A stepping rate of
between 0.25 and 0.5 degrees should suffice for most instances. The amount of di sk space
required decreases substantially if we save 3 segments containing 46 profiles ac ross a 10-degree
bearing range using 0.1 degree bearing steps. In this case, the size decreases f rom 136.8 MB to
only 9.1 megabytes. If the traced rays do not deviate very substantially from th e great-circle
paths, the bearing range could even be reduced from 10 degrees to 5 degrees, whi ch would cut
the required disk space in half again to only 4.56 megabytes. In many instances, particularly
with segments less than about 8,000 kilometers, the number of profiles per segme nt can be
reduced substantially without significantly affecting results.
So selecting wise parameters in suboption #21 of the Comprehensive Options menu will
help you control the amount of disk space consumed when developing three dimensi onal profiles.
This discussion goes into relative detail regarding the way PROPLAB computes
63
ionospheric profiles. If you do not understand the method, reread this section u ntil you do.
Failing that, experiment with PROPLAB. Nothing teaches better than hands-on expe rience.
Keep in mind that PROPLAB PRO contains a useful context-sensitive help system. I f any of the
prompts are confusing or seem ambiguous, press the F1 key for more detailed desc riptions.
3.4.1.4 Understanding the Three-Dimensional Grid
The three-dimensional grid shown to
the right was produced during a sample raytracing session using the comprehensive raytracing technique. It shows one ray entering
the ionosphere and splitting into two
component parts (the ordinary and
extraordinary parts). Unlike the simple raytracing technique, the comprehensive raytracing technique draws a straight line from
the transmitter to the location where the ray
enters the ionosphere. The simple technique
draws a smooth curve showing how the ray
gradually bends upward because of the Earth's
spherical shape.
The comprehensive
technique performs the same computations, but speeds up ray-tracings by simply p lotting a
straight line to the location where the ray penetrates into the ionosphere. This is why the base
part of the ray paths may appear a bit discontinuous. It does not affect the acc uracy of the
tracings at all.
Notice how these two rays (the ordinary and extraordinary rays) each travel inde pendent
paths through the ionosphere. Notice also how the ordinary ray undergoes a chord al reflection
over the equatorial region on its second hop before it returns to the ground. Th e extraordinary
ray also experiences a chordal hop on its second hop. However, unlike the ordina ry ray, the
extraordinary ray becomes trapped between the E and F-layers in a process called "ducting".
Ducting is quite common and can result in extremely long signal paths if the geo metry is right.
Signals that are ducted tend to have a "whispery" tone to them, but in many case s the signals
remain quite intelligible.
The three dimensional grid shown above should be viewed as follows. Imagine the base
of the grid (where the transmitter and receiver reside) forms the inside of a box with only two
sides. In the above example, the far-side of the box forms the "altitude wall". This wall shows
the altitude of the traced rays in the ionosphere. The right-side of the box for ms the "lateral
deviation wall" and shows you the extent to which rays may be deviated laterally (away from the
great-circle path). The great-circle path itself is indicated by the line connec ting the transmitter
to the receiver. This line also forms the 0 (zero) kilometer lateral deviation l ine on the right-side
of the box (the lateral deviation wall). The traced lines curving along the base of the grid
64
indicates the true path the signals take through the ionosphere. In this case, i t is obvious the
traced rays are being deviated away from the great-circle path by ionospheric ti lts and interactions
with the Earths magnetic field.
All distances on the three-dimensional grid are labelled in kilometers. The dist ance
toward the receiver is indicated by the multiple (fairly closely spaced) lines t hat travel along the
base of the grid toward the receiver but perpendicular to the great-circle line. These lines are
then mirrored up onto the altitude wall so it is easier to determine the distanc e of traced rays by
examining the altitude of the ray in conjunction with the distance. The lateral deviation distances
are displayed beside the lines which lie parallel to the great-circle line on th e base grid. These
lines (like the zero kilometer lateral deviation line which forms the great-circ le) are mirrored onto
the lateral deviation wall so that rays which diverge from the great-circle path can be more easily
discerned and measured in distance from the great-circle line.
The key below the grid shows numerous statistics which will be of interest durin g the
tracing of signals. The information displayed is explained below:
Ray Type: Gives the type of ray (ordinary or extraordinary) that is currently being trac ed.
Ordinary rays are colored white. Extraordinary rays are colored yellow.
Elev. Angle: Defines the elevation (take-off) angle used by the transmitting antenna. A val ue
of 0.00 degrees indicates PROPLAB is tracing a ray that was originally "shot" at the horizon.
Azimuth: Lists the azimuth that was used at the transmitter for the current ray being t raced. A
value of 0.00 degrees indicates PROPLAB is tracing a ray that was directed direc tly northward
by the transmitter. It does not indicate the current azimuth of the ray (see the bearing below).
Frequency: Gives the frequency of the ray currently being traced in MHz.
Local Elev: This section defines the elevation of the wave-normal of the ray with respect to the
horizontal. A value of zero degrees means the ray is travelling exactly horizont al. Positive
values indicate the ray is travelling upward at the specified angle. Negative va lues indicate the
ray is travelling downward toward the ground at the specified angle. This value is continually
updated as the ray is traced through the ionosphere.
Ray Lat and Ray Lon: These values identify the current geographical location of the ray being
traced through the ionosphere. Positive latitudes represent northern hemispheres . Negative
latitudes represent southern hemispheres. Longitudes are given in a direction me asured west of
Greenwich and never become negative. Therefore, values between 0 and 180 represe nt western
longitudes and values between 180 and 360 represent eastern longitudes.
Bearing: Defines the current azimuthal bearing of the ray as measured from the transmit ter. In
other words, this value represents the bearing required for the ray to get from the transmitter to
its current geographical location. It is constantly being updated and gives you a good idea of the
65
extent to which non-great-circle deviations may be affecting the ray.
Absorption: PROPLAB integrates the ionospheric absorption equations at the same time it
integrates the ray-tracing equations. It is therefore a highly accurate measure of the total
ionospheric absorption encountered from the time the ray left the transmitter to the current ray
location and far exceeds the accuracy of empirical absorption calculations perfo rmed by most
other propagation programs.
Phase Path: This will likely only be used by those with a deeper knowledge of ionospheric
radio propagation. It indicates the phase path of the ray and is constantly upda ted as the ray is
traced.
Sig.Strength: This value is the computed signal strength of the ray currently being traced. It is
only updated when the ray either penetrates the ionosphere or reaches (or is ref lected) by the
ground. It is given in units of dB (actually dBi or decibels above one microvolt ). Positive
values indicate "hearable" signals. Negative values refer to signals that have l ost most if not all
power to absorption, ground reflections, signal spreading, etc.
Ground Range: This value represents the ground range of the ray away from the transmitter an d
is computed as the great-circle distance of the ray from the transmitter. It doe s not represent the
total geometrical distance (that is, the total distance the ray travels. For this, you must instr uct
PROPLAB to save ray-tracing results to the "RESULTS.OUT" text file. The geometri cal
distance figure is saved to this file along with other valuable parameters such as group path and
polarization.
Ray Azimuth: This value defines the extent to which the currently traced ray is deviating f rom
the great-circle path (in degrees). A value of 0.00 degrees means the signal is precisely following
the great-circle path.
With this information at your disposal, interpreting the results of three-dimens ional raytracings should be easier and more enjoyable.
3.4.1.5 The Text File Ray-Tracing Results
PROPLAB PRO Version 2.0 comes equipped with an option that will save detailed ra ytracing information to a textual disk file named "RESULTS.OUT". The information saved to this
file includes the current altitude of the ray, ground range, phase path, group p ath, geometrical
path distance (that is, the total distance travelled by the ray), absorption, do ppler (if any),
polarization (both real and imaginary parts), the local elevation angle of the w ave-normal
component of the ray with the horizontal, the elevation angle of the ray as meas ured with respect
the transmitter, the azimuthal deviation of the ray away from the great-circle p ath, and the current
azimuth from the transmitter to the ray location. This information almost comple tely describes
the characteristics of the traced rays.
66
Caution should be exercised when saving data to the text file. The size of the f ile can
quickly increase depending on the type of ray-tracing being performed. A single long-distance
traced ray can result in a text file exceeding 50K bytes. Complete ray-tracing s essions saved to
disk may end up exhausting disk space. However, it is the only method that provi des complete
snapshots of traced rays as they are travelling through the ionosphere.
3.4.2 Computing MUFs between any two points
This option makes use of the simple ray-tracing technique only. Automatic computation
of the MUF using the comprehensive ray-tracing technique is currently beyond the capability of
PROPLAB as it would require three-dimensional homing capabilities (an extremely difficult and
time-consuming process), particularly if done in three dimensions. Perhaps it wi ll be attempted
in future versions of PROPLAB.
The second option of the Main Menu lets you compute MUFs for any distance. You a re
requested to enter the latitude and longitude of the transmitter and receiver. I f this has already
been set, simply press ENTER to use those values. PROPLAB next asks you to type in the
distance (in kilometers) for the MUF. If you press ENTER at this prompt, PROPLAB will
automatically calculate the MUF for the distance between the transmitter and rec eiver. If you
specify a distance, the MUF will be computed at that distance on a bearing (azim uth) towards
the destination. PROPLAB will always compute the MUF for the shortest path betwe en the two
points.
PROPLAB rigorously calculates the MUF. That is, it searches for a skip distance that
coincides with the desired MUF distance and selects the maximum frequency at tha t distance.
This is a much more complicated procedure than most algorithms used in simpler p ropagation
programs. Those programs basically compute the MUF using empirical algorithms th at may
assume simplified ionospheric parameters. For example, some routines used by oth er programs
are able to rapidly compute the MUF by referencing very simple models of ionosph eric layers.
Others attempt to take into consideration effects of geomagnetic activity. In ma ny cases, the
results of these programs are fairly accurate, but may completely fail during ge omagnetic storms
or other phenomena.
PROPLAB makes only very few simplifications to help speed up the process of find ing
MUFs. It will only consider two control points on the path between the transmitt er and receiver.
The control points are carefully chosen and a respectable amount of time is cons umed simply
searching for these control points. The MUF for each of these control points is then computed.
The lower of the two MUF's for the two control points is the MUF for the desired distance. This
method of computing MUF's is valid and accurate for a wide range of conditions a nd paths.
During the MUF computations, PROPLAB uses a realistic ionospheric electron densi ty
profile for each control point and traces appropriate rays through these profile s until the MUF
is found. When PROPLAB numerically traces through the ionosphere for these contr ol points,
67
it does so using steps in distance that are approximately 2.5 times larger than those that are
associated with the "Ray Tracing Speed" (see Section 3.3.3). This significantly speeds up
calculations, but may degrade the accuracy of the results slightly. To increase the accuracy of
the MUF computations, decrease the ray tracing speed by decreasing the "Ray Trac ing Speed"
value in the Options Menu (Section 3.3.3).
After PROPLAB has found the MUF, the frequency is displayed along with the
transmission elevation angle required. Using the computed frequency and a direct ional antenna
oriented at the appropriate azimuth and the required angle of elevation, you sho uld be able to
transmit at the maximum usable frequency to the desired receiver location.
You can verify the computed MUF by ray tracing through the ionosphere at the giv en
frequency and sweeping elevation angles around the required angle given. This is what was done
to produce the results given in Figure 2.5. More accurate results can be obtaine d if you ray trace
signals by sweeping the elevation angles using the three-dimensional comprehensi ve ray-tracing
technique. You may be surprised how different the signals behave when effects of the Earth's
magnetic field and ionospheric tilts are considered.
PROPLAB also gives you the option of rigorously computing the FOT, or Frequency of
Optimum Transmission. Normally, the FOT is considered to be 85% of the MUF (0.85 x MUF).
Our definition of the rigorously computed FOT differs. Our definition requires t hat at least 85%
of the radiated transmitter energy is reflected by the ionosphere. The remaining 15% is lost to
space because of ionospheric penetration. In most cases the rigorously computed FOT will be
lower than the MUF. But in many situations, you may see rigorously computed FOTs that
actually exceed the MUF. For example, the MUF may be computed at 23 MHz, while t he
rigorously computed FOT is computed at 26 MHz. This simply tells you that the io nosphere will
reflect 85% of the power at 26 MHz. It is essentially independent of the MUF.
3.4.3 Setting up Regions of Sporadic-E
Since the comprehensive ray-tracing technique does not take sporadic-E into cons ideration,
this section only applies to the simple ray-tracing technique.
The third option of the main menu gives you the ability to define regions of spo radic-E.
For this function to operate properly, you will need a Plate Carree map projecti on available in
your map library. If one is not available, PROPLAB will notify you and return yo u to the main
menu. To create a Plate Carree map, use the utility "MAKEMAP.EXE".
To define regions of sporadic-E, you will need a mouse hooked up to your compute r.
When first selecting this option, you will be asked whether you want to define t he
locations of the transmitter and receiver (by pressing "X") or regions of sporad ic-E (by pressing
"S"). Press "S" and hit ENTER to define regions of sporadic-E.
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If you have a Plate Carree map in your map library, the software will ask you if you want
to use the map present in the map library. If you have more than one Plate Carre e map
projection in your map library, you can select the map you would like to use by skipping the
unwanted maps.
After you have selected the desired map, PROPLAB begins computing the position o f the
auroral ovals and displays the ovals superimposed on the desired map, along with the position
of the grayline, Sun, and the current signal path defined by the transmitter and receiver locations.
In addition, regions of sporadic-E which you may have used in previous runs are displayed onscreen. Altogether, a great deal of information is made available on-screen. You can determine,
for instance, the proximity of the signal path to the auroral zones, where (if a t all) the signal
crosses into the auroral zones, whether the signal spends any time (and how much time) in
daylight or darkness, and even whether the signal crosses regions of sporadic-E. With this
information in-hand, you can begin defining regions of sporadic-E with your mous e.
Moving the mouse moves the mouse cursor on the screen. Regions of sporadic-E are
defined by marking rectangular regions with the mouse cursor. This is done by po sitioning the
mouse cursor to the upper-left corner of the desired sporadic-E region and click ing on the LEFT
mouse button. A corner pointer will be placed on the screen where the left butto n was clicked.
Now move your mouse over to the area where the bottom right corner of the sporad ic-E region
exists and click on the RIGHT mouse button. This defines the rectangular sporadi c-E region.
PROPLAB next asks you to type in the critical frequency of the sporadic-E region . The
value you type here determines how intense the ionization is within the defined rectangular
region. The ionization, in turn, determines the extent of signal refraction and reflection which
can occur in that region. Sporadic-E can vary over wide ranges, from critical fr equencies of only
about 1.5 or 2.0 MHz to critical frequencies as high as 30 MHz under rare condit ions. In most
cases, sporadic-E varies between approximately 2 MHz and 10 MHz with an average maximum
nighttime critical frequency of about 2 to 5 MHz.
Due to the unpredictable nature of sporadic-E, it is impossible to determine for certain
what level of sporadic-E exists at a specific period of time. The only definite way to measure
the critical frequencies of sporadic-E are with vertical ionosondes. But such in strumentation is
usually out of reach of most amateurs and may require special class licenses to operate on the
HF bands, since they can create interference with other broadcasters.
Many ionospheric sounding stations report critical sporadic-E frequencies to the World
Warning Agency (WWA) in Boulder Colorado. The WWA then provides this information in a
coded format to other organizations. Part of the responsibility of the Solar Ter restrial Dispatch
is to decode this data and disseminate it to the general public, researchers, an d other scientific
organizations. The daily summary of ionospheric data can be obtained from the ST D computer
BBS at 403-756-3008 in the Ionospheric Data submenu. Old data is archived into f iles having
the format "iono-xxx.[zip]" where "xxx" is replaced with the first three letters of the month
desired (ex. "iono-nov.zip").
These archived files are available in the director ies
69
"pub/solar/1991", "pub/solar/1992", etc. These daily ionospheric data reports co ntain critical F2layer frequencies, critical sporadic-E frequencies, and much more for many stati ons around the
world. Using these reports, it may be possible to determine exactly what level o f sporadic-E may
have been influencing your region (or your signal path).
Type the critical frequency of the sporadic-E layer (in MHz) at the prompt reque sting this
information, being guided by the data available from the daily ionospheric repor ts, or by
estimating the values according to the guidance given in the preceding paragraph s. Keep in mind
that sporadic-E is very often associated with the auroral zones. During active o r storm periods
of geomagnetic activity, the auroral zones may be filled with regions of sporadi c-E. The
equatorial regions are also areas where frequent sporadic-E can occur, particula rly during the
daytime hours. Middle latitudes observe sporadic-E more during the equinoxes and geomagnetic
storms, but are not restricted to these times. Sporadic-E can occur almost anyti me and anywhere.
Areas within and poleward of the auroral zones are often associated with regions of enhanced Elayer ionization corresponding to critical E-layer frequencies of about 1.5 MHz. High latitude
regions may observe night-time periods of E-layer critical frequencies of this m agnitude on a
near-daily basis. During the night, the critical frequency of the E-layer usuall y drops to about
0.4 MHz. Critical frequencies of 1.5 MHz are sufficient to affect some low-band frequencies.
After the critical frequency of the defined rectangular sporadic-E region has be en entered,
the map is redrawn with the newly defined region of sporadic-E superimposed on t he map, along
with its associated critical frequency.
To select another region, move the mouse to the desired location and click on th e LEFT
mouse button again. If you decide you do not want to define a region at the loca tion marked by
the left mouse button, press the left mouse button a second time to deselect the marked region.
To remove a defined and superimposed sporadic-E region, move the mouse cursor so that it lies
somewhere overtop of the displayed sporadic-E region and click the RIGHT mouse b utton. This
will remove any defined sporadic-E region.
Sporadic-E regions can be superimposed on other regions of sporadic-E.
If you do not have a mouse available, the rectangular geographical coordinates o f the
sporadic-E regions can be inserted into the text file "PROPLAB.ES" in the follow ing format:
"Top-Left-Latitude,Top-Left-Longitude,Bottom-Right-Latitude,Bottom-Right-Longitu de,CriticalFrequency". The quoted section must reside on one line as follows:
+45.32,105.4,+40.67,85.7,6.0
In this example, the top-left geographical coordinates of the rectangular sporad ic-E region are
+45.32 degrees north latitude and 105.4 degrees west longitude. Similarly, the b ottom-right
geographical coordinates are +40.67 degrees latitude and 85.7 degrees longitude. The critical
frequency of this region of sporadic-E is 6.0 MHz.
70
With or without a mouse, you can define up to 99 individual regions of sporadic- E. There
is no limit on the geographical spatial extent of each individual region. They c an be as large or
as small as you like. It may be useful to remember that most regions of sporadic -E are fairly
small in spatial extent, covering an area perhaps several hundred kilometers in extent. This is
generally true except perhaps in the auroral zones where Es may be more widespre ad and cover
areas many hundreds of kilometers in extent. Polar regions of Es usually exist i n bands or
ribbons extending across the polar cap in roughly the direction of the Sun.
To quit defining regions of sporadic-E, press the ESCape key on your keyboard. T he
regions of sporadic-E that you defined (or edited/removed) will be saved to disk under the text
file "PROPLAB.ES".
You can save screen images while in this mode by pressing the "G", "P", or "S" k eys.
These functions save screen images in GIF image formats, PostScript-compatible f ormats, or a
special format as described below, respectively. Pressing "S" saves screen image s in a special
format. Such saved screen images can be used in other functions of PROPLAB to (f or example)
superimpose contours of ionospheric characteristics, or generate broadcast cover age maps. Maps
of different types can in this way be combined into a single image. For example, the screen
image saved while in this mode provides positional information of the auroral zo nes, the
sunrise/sunset grayline, the position of the Sun, the signal path, and regions o f sporadic-E. Using
this "S"ave function, you can combine this map with contours of maximum usable f requencies,
and/or contours of maximum F2-layer heights, and/or contours of solar zenith ang le, and/or with
broadcast coverage maps, etc. The end-result could be a screen image loaded with invaluable
information.
3.4.4 Setting up Transmitter and Receiver Locations
The third option of PROPLAB's Main Menu gives you the ability to define regions of
sporadic-E or transmitter/receiver geographical positions. Select the latter by pressing "X"
followed by ENTER. Setting up the transmitter and receiver locations has been de scribed in
detail in Section 3.3.2. Refer to that section for more information.
After you have defined the transmitter and receiver locations, press the ESCape key on
your keyboard to return to the PROPLAB Main Menu.
3.4.5 Plotting Electron Density Profiles
The fourth option of the Main Menu will plot electron density profiles for any S INGLEHOP path MIDPOINT specified. The midpoint is defined as that point that lies half-way between
the transmitter and receiver on the great-circle path. If the great-circle dista nce exceeds 4,000
kilometers, only the profile for the midpoint of the FIRST HOP is used. This is useful for
determining ionospheric conditions at any path midpoint. To determine conditions at the
71
transmitter geographical location, set the receiver geographical position to the transmitter position
so the path midpoint lies over the transmitter location. For example, if the tra nsmitter was
located at 40N 105W and the receiver was located at 45N 75W, to determine the io nospheric
electron density profile at the transmitter, use the Options Menu to set the rec eiver geographical
coordinates to 40N 105W. The midpoint obviously therefore must also be 40N 105W, which is
the desired profile location. Similarly, to see the profile at the receiver loca tion, set the
transmitter location equal to the receiver location. In this case, the transmitt er and receiver
geographical positions would be set to 45N 75W respectively.
PROPLAB will plot the electron density profile for any geographical location, an y time
of day, and any date, up to an altitude of 1,000 kilometers. When the geomagneti c A-index is
equal to 5, this profile exactly coincides with the output of the International Reference
Ionosphere. For larger values of geomagnetic activity, the electron density prof ile may be altered
according to the strength of magnetic activity, the geographical position of the profile, and other
known influencing parameters.
Electron density profiles provide you with a wealth of information at a glance. For
example, you can determine exactly at what height the maximum electron density o ccurs. You
can determine the magnitude of E-layer ionization and learn how the profile chan ges from
daytime conditions to night-time conditions. You can examine approximate effects of
geomagnetic activity on the profile characteristics, and can determine at what a ltitude ionization
begins in the ionosphere for daytime and nighttime conditions. As well, if spora dic-E is present,
you can see the spike in electron density that exists in the narrow region where sporadic-E exists.
This is a useful function for determining the overall internal "shape" of the io nosphere at
any given time, date, or level of geophysical activity for any geographical posi tion.
3.4.6 Displaying Ionospheric Profile Statistics
The fifth, sixth, and eighth through eleventh options of the Main Menu will be c overed
in detail shortly. But first, we will examine what the seventh option of the Mai n Menu does.
Selecting this option will display ionospheric profile statistics on-screen at t he midpoint between
the transmitter and receiver (just as described in the previous section).
After the ionospheric electron density profile has been computed and adjusted (i f
necessary), information describing the properties of the ionosphere are displaye d in a textual
format on-screen.
At the top of the screen, the UTC date and time are given, along with the transm itter
geographical position (given as the "Origin"). The next line lists the sunspot n umber and
geomagnetic A-index values that were used to generate the profile statistics, as well as the
geographical path midpoint position. This is the location where the profile stat istics are valid.
72
The next four lines define the characteristics of the F2 layer. The first line l ists the
critical frequency of the F2 layer for both quiet (A-index of 5) and disturbed o r "dynamic" times.
The dynamic value is an estimated critical frequency determined after taking geo magnetic
activity, magnetic latitude and longitude, etc, into consideration. The next lin e lists the
ionospheric M-factor for distances of 3,000 kilometers during quiet conditions. The M-factor is
the ratio between the maximum usable frequency for a distance of 3,000 kilometer s and the
critical frequency. Using this value and the quiet-time F2-layer critical freque ncy value, you can
determine the MUF by multiplying the two values together. For example, if the cr itical F2-layer
frequency was 4.436 MHz and the M-factor was 3.13, the MUF for a distance of 3,0 00
kilometers (also written as "MUF(3000)") would be: 4.436 x 3.13 = 13.885 MHz. Fo r distances
less than or greater than 3,000 kilometers, it is necessary to perform interpola tion or extrapolation
on the data. However, this is unnecessary since the MUF for given distances can be directly
determined through the use of the second Main Menu option (Compute MUFs). The ma ximum
F2-layer height is listed on the next line. The height where the electron densit y for the F2-layer
reaches a maximum is known as the maximum F2-layer height, or hmF2. The value fo r quiettime and dynamic conditions is given. The dynamic value is a quick estimate and may be more
accurately determined by producing an electron density plot for the same region. You will notice
that as the level of geomagnetic activity increases, the height of maximum elect ron density also
tends to increase. The final of these four F2-descriptive lines gives you the ma ximum electron
density of the F2-layer for both quiet and dynamic conditions. These values will exactly coincide
with plotted electron density profiles.
The next three lines are for F1-layer statistics. The first of these three lines defines the
critical frequency of the F1-layer, if it is present. If the F2-layer ionization overlays the F1-layer
maximum, then the F1-layer critical frequency is invalid and is listed here as z ero. If the F1layer maximum is not influenced by the F2-layer, then the critical frequency is listed here in
MHz. The value given will be similar for both quiet and dynamic conditions. Geom agnetic
activity has a heavier impact on the F2-layer characteristics. The maximum elect ron density of
the F1-layer is listed last, if the F1-layer maximum can be separated from the l ower-side of the
F2-layer. If the F1-layer maximum cannot be differentiated, the density value li sted on this line
is given as zero.
The next six lines displayed define the characteristics of the E and D regions o f the
ionosphere - three lines for each region. The first three lines define the E-reg ion critical
frequency, the E-region maximum height of electron density, and the associated E -region
maximum electron density. You will notice that the maximum height of electron de nsity of the
E-region is generally fixed at 105 kilometers. The three lines devoted to the D- region are the
same as those for the E-region. Specifically, the first line defines the D-layer critical frequency
(which you will notice is significantly smaller than the critical frequencies of the other layers).
The final two lines list the height of the maximum D-region electron density, an d the maximum
electron density of the D-region itself.
The final four lines of the display show related statistical quantities that are fairly
important for determining the ionospheric profile. The first line lists the sola r zenith angle for
73
the time, date, and geographical position of the profile. The solar zenith angle is the angle of
the Sun measured from the zenith (straight up). It is different from the solar e levation angle
(which is also listed here) in that the solar elevation angle is the angle measu red from the horizon
to the Sun in the sky. The solar zenith angle is measured from the zenith instea d of the horizon.
Therefore, a solar zenith angle of 90 degrees corresponds to a solar elevation a ngle of zero
degrees, which represents the position of the sun directly on the horizon 90 deg rees away from
the zenith. Likewise, a solar zenith angle of zero degrees corresponds to a sola r elevation angle
of 90 degrees and represents the position of the sun directly overhead at the ze nith. The second
line gives the solar declination angle, or the angle above or below the solar eq uator where the
Sun appears directly overhead at 12 noon. Because of the orbit of the Earth arou nd the Sun, this
angle varies by about +/- 23 degrees. At the seasonal equinoxes (spring and fall ), the solar
declination angle is about zero degrees. Therefore, during these times, the Sun would appear
directly overhead at noon, over the equator. The third line gives you the magnet ic latitude and
longitude of the geographical position used in the profile statistics. The geogr aphical position
of the profile statistics is given in the second line of the display after the " Profile Location". The
final line of this display shows you the magnetic DIP (or inclination) angle at the current
geographical profile location.
To return to the PROPLAB Main Menu, press the ENTER key.
3.4.7 Quitting PROPLAB and returning to DOS
To leave PROPLAB's Main Menu and exit to the DOS prompt, simply select the twelf th
option of the Main Menu or press the ESCape key.
SECTION 4 - GLOBAL IONOSPHERIC MAPS
A substantial amount of PROPLAB's power lies in its ability to generate practica lly any
type of map for almost every type of ionospheric parameter relevant to radio com munications.
The maps resemble weather-type maps and use complex contouring algorithms to pro duce
contours of equal values. By selecting the fifth option of PROPLAB's Main Menu, you gain
access to this large base of power. This section will describe the available typ es of maps that
can be generated and how they can be used.
You retain full control over how you want the maps generated, right down to the color
for the contour lines.
All of the different maps require you to enter specific common information: the date, time,
sunspot number, geomagnetic A-index (or press ENTER if not available), sunspot n umber, map
74
resolution level, type of map projection to use, type of map to generate, contou r specifications,
ionospheric model to use, and the contour color to use.
The date, time, sunspot number, geomagnetic A-index, and type of map to generate are
self-explanatory inputs and need no further discussion. The others need to be ex plained in
slightly greater detail before reliable use of these powerful functions can be e xpected.
For each map generated, you will be asked to select a map resolution level. This
determines how spatially accurate the map is for the given date and time, etc. T here are five
different resolution levels that can be selected. The lowest resolution level pr oduces maps much
quicker than higher resolution levels, but the spatial accuracy of the map may b e lacking. In
other words, some features that may be present might not be shown in the lower r esolution maps.
The resolution level varies according to the type of map projection you select. For
example, the spatial resolution and accuracy of a global Lambert map projection can be
approximately doubled if a polar-map projection (such as an orthographic project ion) is used.
Why? Simply because a polar-map projection includes only half the surface area o f a global
Lambert projection, which permits PROPLAB to compute ionospheric parameters for more of the
available surface area. A polar projection only includes those geographical area s that are either
north or south of the equator. A Lambert projection includes both the north and south
hemispheres and hence twice the surface area. Ionospheric profiles must therefor e be computed
for larger spatial distances when larger spatial areas are included. For greates t spatial resolution,
select the highest available resolution levels and use polar map projections.
PROPLAB gives you full control over how contours are to be labelled. One of the
common inputs required defines how you want contours to be labelled. The default is to label
all contour lines. You can also instruct PROPLAB to label only every Nth contour , only the
lowest and highest valued contours, or not to label any contours at all. Usually , you will want
to label all contours, although in cases where the labelling from contours may o verlap one
another, it may be useful to label only every other contour, etc. The choice is yours.
PROPLAB also asks you for the minimum value to contour, the maximum value to
contour, and the stepping rate for contouring between the minimum and maximum va lues. For
example, to create a global map of MUFs with contours defining the 5, 10, 15, 20 , 25, and 30
MHz MUF zones, you would specify a minimum contour value of 5, a maximum value o f 30,
and a stepping rate of 5 (MHz). By pressing ENTER at each of these prompts, the software
automatically contours from the minimum computed value to the maximum computed v alue at
step increments that would result in maximum contour resolution. In other words, by default,
PROPLAB will produce maps with the greatest number of possible contours. PROPLAB will
allow up to 25 individual contour lines per generated map.
PROPLAB also gives you the ability to define what color to use when drawing cont ours.
You can select one of 15 different colors. The default color is light cyan.
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If you have previously saved a map with information on it such as the sunrise/su nset
grayline, location of the auroral zones, signal path, etc, you can inform PROPLA B to use a
previously saved map and superimpose all contours on that map. This powerful fea ture lets you
integrate maps of different types and superimpose contours on those maps. For ex ample, by
pressing the "S" (for Save") key while editing sporadic-E regions or graphically setting new
transmitter and receiver points, you can save the screen image to disk and later use that same
map projection to superimpose contours of ionospheric quantities.
While PROPLAB is drawing contours, a small box will flash red and white at the t op
right-hand corner of the screen. This is used to tell you that PROPLAB is busy t hinking. You
can abort the drawing process anytime by pressing the ESCape key. When PROPLAB h as
finished drawing contours, the box disappears and a label identifying the type o f map completed
is printed on the screen. You can then press the "S" key to save the screen imag e for integration
in other functions or for superimposing other contours on the same map. You can also press the
"G" key to save a copy of the screen image as a GIF image file. Or, you can pres s the "P" key
to save the screen image in a PostScript-compatible file for printing to a laser printer.
4.1 Global Maps of Critical F2-Layer Frequencies
These very useful maps provide you with instantaneous information regarding worl d-wide
critical F2-layer frequencies. A sample map is shown in Figure 4.1.
This Figure was produced
by PROPLABs "CONTOUR.EXE"
utility (invoked by Main Menu
Option #5) and is exceptionally
valuable for radio communicators.
It shows you the critical
frequencies of the F2-layer
throughout the world, at a specific
date and time, level of
geomagnetic activity, and sunspot
number. Using the information
from this map, it is possible to
determine where horizontal
gradients exist in the electron
density profile that might cause
non-great-circle propagation. It is
also used to determine maximum
usable frequencies, the general
state of the ionosphere, etc.
Figure 4.1: Global Map of Critical F2-Layer Frequencies
Recall that the critical F2-layer frequency is the maximum frequency that can be reflected
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vertically from the F2-layer. Since the F2-layer is usually the main layer respo nsible for
ionospheric signal refraction, it is sometimes called the vertical penetration f requency because
on frequencies higher than the F2-layer critical frequency, vertically propagate d signals will
penetrate the ionosphere.
There are several features of interest to point out here. Notice the high critic al frequencies
near the equatorial region. These enhanced foF2 values are known as the equatori al anomaly.
They occur within approximately +/- 20 degrees of the magnetic equator, not the geographic
equator. This is why the increased values tend to drift into South America away from the
geographical equator - the magnetic equator dips below the geographical equator and reaches a
maximum difference near South America.
Regions where the sun is rising or setting produce pronounced changes in the ele ctron
density profile that are easily discerned in the sample foF2 map given in Figure 4.1 for 19:00
UTC. At this time, it is near noon for the North American region and critical F2 -layer
frequencies (and hence F2-layer ionization levels) are at a maximum for the day. Toward the
west (toward the sunrise sector) the critical F2-layer frequencies begin decreas ing. Critical F2layer frequency gradients are strongest near eastern Australia where the sun is rising and the F2layer is being rapidly ionized. Gradients can be determined by examining how clo se the foF2
contours come to each other. In general, the stronger the gradient, the less sta ble the ionosphere
is and the more likely signals will experience non-great-circle propagation thro ugh resulting
horizontal tilts in the electron density gradient. PROPLAB will not take horizon tal tilts into
consideration for computing possible non-great-circle paths. Future versions of PROPLAB may,
however.
Radio signals which are propagating through the ionosphere are most stable where the
contour gradients are weakest (or farthest apart), OR when signals use paths tha t FOLLOW the
gradient contours. The latter may require further explanation. Signals that pass through highgradient regions are more susceptible to non-great-circle propagation and may ex perience less
stable conditions. However, these effects can be minimized if paths are chosen t hat follow (as
closely as possible) the contour lines in high-gradient zones. For example, on t ransmissions from
eastern Australia to Mexico, the signal path crosses the foF2 contours at almost perpendicular
angles. In other words, the signal path goes AGAINST the gradient of the contour s and is more
likely to experience non-great-circle propagation and instabilities. Under these conditions,
PROPLAB may be less accurate than usual, particularly on sunrise-crossing circui ts. On the
other hand, a signal path from eastern Australia to the southern tip of South Am erica more
closely follows the foF2 contours and GO WITH THE GRADIENTS. For this signal pat h,
greater signal stability and less non-great-circle propagation would likely be o bserved. It is
interesting to note that in this last signal path, the signal is essentially a " grayline signal", or one
which follows closely along the sunrise-sunset terminator.
Maps produced with geomagnetic A-index levels less than or equal to 5 can be con verted
to monthly median maps if the sunspot number or solar flux value used is the ave rage value for
the last 12-months. By offsetting the geomagnetic A-index or sunspot number, it is possible to
77
adjust the maps for conditions that may more closely represent observed conditio ns. In general,
the geomagnetic A-index for the current UTC day as well as the sunspot number or solar flux
value averaged over the last week or two, are sufficiently accurate inputs to mo del approximate
observed conditions. It must be remembered that daily maps of foF2 may differ ma rkedly from
those produced here, since the ionosphere is still a highly unpredictable region of our atmosphere.
4.2 Global Maps of Ionospheric M-Factors
M-factors were discussed previously and represent the ratio between the maximum usable
frequency for specific distances and the critical F2-layer frequency. For exampl e, an M-factor
for a distance of 3,000 kilometers would be computed by dividing the MUF for a p ath distance
of 3,000 kilometers by the critical frequency of the F2-layer at the midpoint of that path.
Numerically it is defined as:
M(3000)F2 = MUF(3000) / foF2
From this, if we know the critical F2-layer frequency (from an ionogram or stati on report),
we can determine the MUF for a distance of 3,000 kilometers by multiplying the c ritical F2-layer
frequency (foF2) by the M-factor for the same distance.
M-factors are therefore ratios of two ionospheric quantities. Producing global i onospheric
maps of these factors can help determine how the MUF and foF2 are related. They can also be
used together with maps of foF2 to compute MUFs for any part of the world.
4.3 Global Maps of Maximum Usable Frequencies
Out of all of the global maps produced by PROPLAB, these maps will perhaps be th e
most heavily used. For this reason, it is important that the maps be interpreted correctly and
wisely. The following discussion uses the sample maximum usable frequency map in Figure 4.2.
This figure was produced for the same date, time, sunspot number, and level of
geomagnetic activity as was used in Figure 4.1. They can be directly compared. T he similarities
are obvious. Maximum usable frequencies occur in the same regions as maximum F2- layer
frequencies shown in Figure 4.1. Similarly, maximum contour gradients occur wher e the sun is
either rising or setting. The most pronounced and easily defined is the sunrise sector. This is
because the F2-layer electron density (and hence critical frequency) decreases s lower during
sunset than it increases during sunrise. In other words, the critical frequency changes more
abruptly and systematically during sunrise than it does during sunset. Higher F2 -layer critical
frequencies will produce correspondingly higher MUFs for given distances, since the increased
F2-layer ionization will reflect signals with higher frequencies. The map in Fig ure 4.2 shows
MUFs in MHz for a path distance of 3,000 kilometers.
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When
instructing
PROPLAB to produce global maps
of MUF, you will be asked what
distance to compute MUFs. The
default is 3,000 kilometers. Most
of the critical parameters for 3,000
kilometer MUFs have been
precalculated. Producing default
3,000 kilometer MUF maps are
therefore significantly faster than
producing maps of different path
lengths.
Specifying paths of
different lengths will force
PROPLAB to rigorously compute
MUFs for those distances by
quickly ray-tracing through the
Figure 4.2: Global Map of MUFs for 3,000 kilometers
ionosphere until the MUF for the
given distance is found. This can
be a time-consuming process, particularly on slower computers or if high map res olution levels
are chosen. However, the results can be very informative and helpful.
It is important to understand how to correctly interpret MUF maps. To help us in this
regard, let's examine how to correctly interpret the results of the map in Figur e 4.2. Since this
map shows the MUF for a distance of 3,000 kilometers, each point on the map is t he MIDPOINT
of a 3,000 kilometer path. For example, this map shows that South Africa has an MUF of 9
MHz for a distance of 3,000 kilometers. Therefore, if the MIDPOINT of your 3,000 km signal
path passed over South Africa, you could expect to see an MUF of 9 MHz. Phrased a little
differently, the MUF for a transmitter situated 1,500 kilometers (the path midpo int) away from
South Africa would be 9 MHz if the signal passed over South Africa. This map wou ld not apply
for signals with greater or smaller path distances. It only applies for signals that travel 3,000
kilometers in ground distance.
This is exceptionally useful information and can help you determine optimum freq uencies
to use throughout the day for specific paths. It can also help you determine how long you can
expect MUFs to remain above a specific frequency before MUF failure occurs. Noti ce that the
smallest maximum frequencies occur during the nighttime and early morning hours, while the
highest MUFs occur when the Sun is high in the sky near local noon. And as was e xplained
with the foF2 maps, the highest gradients in MUF occur near sunrise, near the eq uatorial
anomaly, and near sunset.
Over time, you will gain experience in using and applying these maps and will be gin to
learn how the ionosphere responds to the seasons, and even events such as geomag netic storms.
For example, MUFs may increase over the equatorial regions during geomagnetic st orms, while
decreasing substantially as the latitude is increased.
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4.4 Global Maps of the Height Maximum of the F2-Layer
The maximum height of the F2 layer is a critical parameter that can strongly inf luence
the distance related to a given maximum usable frequency. For example, if the MU F over the
U.S. is fixed at 25 MHz for a distance of 3,000 kilometers, increasing the heigh t of maximum
electron density in the F2-layer would increase the distance for which this MUF applied. It may
also increase the actual MUF. Decreasing the height maximum of the F2 layer (als o known as
the hmF2) would decrease the distance for which the MUF applied, and may also de crease the
actual MUF.
Gradients in hmF2 can also change the path of a signal from one which follows th e greatcircle to one which deviates therefrom. Using paths that are both stable in crit ical frequency and
stable in hmF2 usually give reliable and often strong signals. These are the pat hs which should
be sought if communication reliability desired. If reliability is not as signifi cant as MUF, then
greater emphasis should be given to maps of maximum usable frequencies.
The height maximum of the F2-layer responds rapidly to changes in geomagnetic ac tivity.
Usually, the hmF2 increases as geomagnetic activity increases over the middle an d high latitudes,
since heating in the lower portion of the F2 layer erodes the ionization of that portion of the
ionosphere and causes the maximum height of the electron density to increase. Th is may sound
good from the point of view of increasing transmittable distances, however incre ases in
geomagnetic activity are also accompanied by an attended decrease in F2-layer el ectron density
(and hence critical frequencies) for the same reason as given above. This reduce s the MUF over
all affected regions. As it turns out, the reduction in foF2 is usually more imp ortant than
increases in hmF2. And since any increase in hmF2 is usually accompanied by a de crease in
foF2, any positive effects of increasing hmF2 are nullified.
4.5 Generating Maps of Critical E-Layer Frequencies
The critical frequency of the E-layer (or foE) is heavily dependent on the locat ion of the
Sun. For high solar elevation angles (or low solar zenith angles), the critical frequency of the
E-layer reaches a maximum of between 3 to 4 MHz. That is, the frequency which wo uld cause
a vertically propagated signal to penetrate the E-layer would be between 3 and 4 MHz if the Sun
were high in the sky. As the Sun drops toward the horizon, critical frequencies drop. After the
Sun sets, ionization in the E-layer abruptly ends and critical frequencies fall even further.
Minimum critical frequencies are observed around local midnight with foE values of about 0.4
MHz.
It is important to keep in mind that foE is dependent upon sporadic-E and enhanc ed
nighttime E-layer ionization (perhaps caused by auroral electron precipitation, etc). Sporadic-E
can increase foE by many times. For example, normal nighttime foE is around 0.4 MHz. A 5
MHz sporadic-E critical frequency would increase the nighttime foE value for aff ected regions
80
to 5 MHz, which is a factor of 12.5 times greater than the normal nighttime foE value. These
contoured maps of critical E-layer frequencies do not take these sporadic phenom enon into
consideration, even if they are identified with PROPLAB as regions of sporadic-E . Only the
regular non-deviative foE values are used in these plots.
4.6 Producing Maps of Solar Zenith Angles
These types of maps are exceptionally valuable when determining possible effects of solar
flares on signal paths. Maps of solar zenith angles show the elevation angle of the Sun away
from the zenith, or the point straight up overhead. A solar zenith angle of zero degrees
corresponds to the point exactly straight up overhead. A solar zenith angle of 4 5 degrees
corresponds to a point half-way between the horizon and the zenith. Similarly, a solar zenith
angle of 90 degrees corresponds to a point directly on the flat horizon. Solar z enith angles of
90 degrees therefore denote areas of the world that are undergoing either sunris e or sunset. Solar
zenith angles greater than 90 degrees denote areas of the Earth that are in dark ness or twilight.
Astronomical twilight typically ends (or begins) when the sun reaches a solar ze nith angle of
about 102 degrees (or about 12 degrees below the horizon).
During solar flare activity, maps of solar zenith angle are of primary importanc e for
determining what areas of the world may be experiencing short wave fadeouts (or SWFs). A
short wave fadeout is a period of time when shortwave (HF) signals suddenly (or gradually) fade
out and disappear. As flares increase in magnitude, frequencies which can be aff ected by the
activity increase. For example, a magnitude M1.0 flare may produce a SWF affecti ng frequencies
up to 7 MHz. Compare this with a magnitude X1.0 flare, which may produce an inte nse SWF
affecting frequencies as high as 15 or 20 MHz - effectively wiping out communica tions on most
HF bands.
The extent to which flares affect communications depends on the solar zenith ang le. Low
solar zenith angles (or times when the Sun is high in the sky) result in the str ongest SWFs and
affect frequencies higher than at any other location on the Earth. As the solar zenith angle
increases toward sunset or sunrise conditions, the effects of flares decreases. For solar zenith
angles greater than 90 degrees (when the Sun is below the horizon), flares do no t have any
significant adverse effects on signal absorption, since the ionizing radiation i s not impinging on
the ionosphere when the Sun is not in the sky.
For these reasons, you can utilize the maps of solar zenith angles to determine where the
strongest SWFs may be observed.
4.7 Producing Maps of Magnetic DIP Angles
PROPLAB will produce maps of magnetic DIP (or angles of inclination). Since many
parameters in radio propagation are dependent on the magnetic DIP or inclination angle, these
81
maps may be useful in the study of radio propagation. They are included here for convenience.
Magnetic DIP angles do not change substantially over time, and are not dependent on sunspot
number or geomagnetic activity even though you may be required to input these va lues (they are
common inputs for all maps).
4.8 Global Maps of Magnetic Field Total Intensity
PROPLAB uses models of the Earth's magnetic field. One of the modelled parameter s
required for determining ionospheric characteristics and propagation conditions, is the total
intensity of the magnetic field. You can map this parameter using this option. A s with the
magnetic DIP angles, this parameter does not change significantly according to s unspot number,
time, or geophysical activity and is included here for reference purposes. Label led contours are
in units of gammas (or nanoteslas).
4.9 Global Maps of Magnetic Latitude
It is often useful to know what magnetic latitude certain features of the Earth are located
at. Since radio propagation is closely linked with magnetic latitude, it may be useful to know
where a signal travels in relation to magnetic latitude. This option gives you t he ability to map
magnetic latitude.
4.10 Producing Maps of Modified DIP Angles
PROPLAB uses, in addition to the regular DIP angle calculations, a modified DIP angle
equation that is more accurate in determining certain ionospheric characteristic s. This option lets
you map the modified DIP angles.
4.11 Transverse Plasma Frequency Maps
An exceptionally powerful and useful map available with PROPLAB is the transvers e
plasma frequency map. Imagine slicing the ionosphere vertically with a knife and looking at that
sliced portion edge-on. This is what the transverse plasma frequency map provide s. It is
analogous to cutting a tree down and examining the internal rings. What you see in a transverse
plasma frequency map is a cross-section of the ionosphere - the actual internal structure as it
varies with height.
Why is a transverse plasma frequency map so valuable? Because it shows you where
ionospheric tilts exist that can cause non-great-circle propagation. It shows yo u the various layers
of ionization in the ionosphere and gives you information on their locations, in tensities, etc. For
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example, Figure 4.3 is a hypothetical crosssection of the ionosphere for the path between
northern Mexico and eastern Australia at
19:00 UTC on 15 July 1994 using a sunspot
number of 100 and an A-index of 5. The
transmitter is at the far left of the figure and
the receiver is at the far right. Distances are
given at the base of the figure in units of
kilometers. Height is also given in units of
kilometers with height intervals every 50
kilometers labelled. This figure therefore
shows a cross section of the path between
Mexico and Australia (a ground-distance of
over 12,000 kilometers) to an altitude of 450 Figure 4.3: Transverse Plasma Frequency Map
kilometers. The contour lines are plasma
frequencies of the ionosphere. Plasma frequencies are essentially critical frequ encies for specific
heights in the ionosphere. For example, at the base of the ionosphere, the plasm a frequency
given in Figure 4.3 is 0.2 MHz. This means that a vertically-propagated signal b elow 0.2 MHz
would be reflected from this base-layer, while frequencies above 0.2 MHz would p enetrate the
ionosphere at that level and travel upward until the plasma frequency increased above the
operational frequency. The plasma frequency then, is the frequency of a signal r equired to
penetrate a specific density of electrons. The plasma frequency is related to th e electron density
through the following equation:
Density = (1.24 x 10 10) * Plasma Freq
The plasma frequency is given in MHz, and the electron density is in electrons p er cubic meter.
For example, a plasma frequency of 8 MHz is associated with an electron density of 9.92 x 10 10
electrons meter -3. That is, a frequency of 8 MHz would be reflected from an ionospheric layer
when the electron density of that layer increased to 9.92 x 10 10 electrons per cubic meter.
Referring to Figure 4.3 above, Australia is on the verge of sunrise, while Mexic o is
experiencing conditions at approximately noon. Concentrate on the far right side of the map
nearest Australia. As you travel from right (Australia) to left (toward Mexico), the electron
density of the D and E regions begins increasing. The contours illustrate this. There is also an
attendant rapid increase in the electron density associated with sunrise in the F region of the
ionosphere (above 150 km). This region of the ionosphere is tilted. A non-tilted ionosphere
would be one where the contours are horizontal and flat. In this case, there is considerable tilt
as you travel from Australia toward Mexico (or visa-versa), particularly in the distance range
between 5,000 and 10,000 kilometers from Mexico. These are areas where non-great -circle paths
may be observed.
Figure 4.3 also shows what happens as signals pass through the equatorial region . As was
mentioned earlier, the height of maximum electron density in the ionosphere incr eases as the
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magnetic equator is approached. This is clearly visible in the transverse plasma frequency map
as an increase in the height of the iso-ionic contours from Mexico (at zero km's ) to about 5,000
kilometers where the ionospheric layers have increased in height by about 50 to 100 kilometers.
For signals striking these ionospheric layers at the appropriate angles, chordal -hop type
propagation may be possible due to the tilting of the ionosphere on both sides o f the equator.
In this case, the magnetic equator is located at approximately the 5,000 km mark .
PROPLAB will produce transverse plasma frequency maps or cross-sections of the
ionosphere for any signal path. You simply specify the geographical locations of the transmitter
and receiver and tell PROPLAB how high (up to 1,000 km) in the ionosphere to map , and
PROPLAB will do the rest.
For greater accuracy on very-long paths such as the one from Mexico to Australia , divide
the path into segments and generate transverse maps for each of those segments. The spatial
resolution of the maps is dependent on the distance between the transmitter and receiver. For
example, the ionospheric electron density profile for a 12,000 kilometer path is determined
approximately every 500 kilometers, whereas the ionospheric electron density pro file for a 4,000
kilometer path is computed approximately once every 170 kilometers, giving a hig her level of
spatial resolution in the map. You can approximate the interval used to determin e profiles by
dividing the path distance by about 24. For example, a 12,000 km path divided by 24 gives a
spatial interval of about 500 km.
A word of caution is required when generating transverse plasma frequency maps w ith
levels of geomagnetic activity above the quiet level (about 5). The contouring m ethods employed
by PROPLAB may cause incorrect interpolations in the electron density, not becau se the
contouring methods are inaccurate or incorrect, but because the spatial interval s that must be used
to produce the maps may be too large and may leave ambiguities in the gaps that are difficult
for the contouring algorithms to accurately interpolate over. These regions of p ossible erroneous
contours typically occur with higher levels of geomagnetic activity, particularl y those associated
with major to severe storming (A-indices above 50 to 100). They appear on the is o-ionic contour
maps as false-"bubbles" in the electron density that occur at regularly spaced i ntervals. These
inaccuracies with higher levels of geomagnetic activity will be corrected in fut ure revisions to
PROPLAB. The iso-ionic contours associated with quiet-time conditions are more a ccurate and
reliable.
SECTION 5 - SIMPLE RAY TRACING SCREEN
The heart of PROPLAB is the engine which traces rays through the ionosphere.
PROPLAB PRO Version 2.0 has two hearts. This section deals only with the simple ray-tracing
engine. It is an entire subprogram in itself and is the file named "MODEL.EXE". This program
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requires PROPLAB to tell it what to do and how to do it. MODEL.EXE then performs the
requested ray-tracing functions and returns the results back to PROPLAB's main m odule.
The ray tracing screen has a large amount of information that can be (optionally ) updated
at regular intervals while a ray is being traced. This brief section describes t he information that
is available on the ray-tracing screen.
5.1 Location, Azimuth, Distance of the Transmitter/Receiver
The first six lines of the left-side panel of the ray-tracing screen define the geographical
positions of the transmitter and receiver. It also lists the distance from the t ransmitter to the
receiver in kilometers, and the azimuthal angle which should be used to transmit from the
transmitter to the receiver. This angle is reckoned east of due north. For examp le, an angle of
90 degrees azimuth represents a position pointing directly to the east. An angle of 180 degrees
points directly south, etc.
5.2 UTC Time and Operational Frequency
The time and frequency of the ray being traced can be found in the seventh and e ight
lines of the top-left panel of the ray-tracing screen. The time given here is al ways Universal
Time. The frequency is always in units of MHz. Although only the first four deci mal places of
the frequency are printed, input frequencies can be much more accurate, extendin g down to seven
or eight decimal places for increased accuracy.
5.3 CUR Lat and CUR Lon Statistics
These are valuable statistics that can help you diagnose where various types of signal
anomalies or features occur. They represent the CURrent latitude and CURrent lon gitude of the
signal, as it is being traced through the ionosphere using the azimuth given in Section 5.1. Using
this feature, you can determine the geographical coordinates where your signal p enetrates into
the ionosphere, or where it crosses into the auroral zone, or where the signal l oses much of its
quality, or the locations of ground-hops, etc.
5.4 Signal Air Distance Statistic
The distance a signal travels from a transmitter to a receiver is not the same a s the
straight-line ground-distance from the transmitter to the receiver. The signal m ust travel further
than the ground-measured great-circle distance because not only is the signal tr avelling
horizontally toward the receiver, but it is also travelling upwards and downward s into and out
of the ionosphere. The "AIR DIST" or air-distance statistic shows you how far yo ur signal has
85
actually travelled, not the ground-measured great-circle distance usually report ed by propagation
software.
5.5 CURrent Angle of the Signal
As a signal travels from the transmitter to the receiver, the angle of propagati on of the
signal will change from one instant to another. For example, a signal that is sh ot at a zero degree
elevation angle, directly at the flat horizon, will increase in height by about 1 kilometer every
112 kilometers of distance it travels because of the spherical shape of the Eart h. To prove this,
hold a ruler flat against a sphere and see if the distance from the ruler to the center of the sphere
increases with distance along the outstretched ruler. This statistic simply tell s you what elevation
angle the signal is headed at. It is measured from the horizontal position. That is, a zero degree
angle denotes a signal travelling exactly horizontal toward the horizon. A signa l that is travelling
at a 90 degree angle is directed straight up toward the zenith. Positive angles are directed toward
the zenith, negative angles are directed toward the center of the Earth. So, as a signal travels
through the ionosphere, it will be associated with a positive angle of ascent in to the ionosphere.
Ionospheric refraction will gradually decrease this angle until it is travelling approximately
horizontal, after which further refraction will cause the ray to bend downward. This is indicated
by a negative angle value. Negative 90 degrees is therefore pointing straight do wn.
The small box to the left of the geographical coordinates of the transmitter and receiver
(in the top-left panel of the ray screen) is a graphical representation of the c urrent angle of the
travelling ray. It shows the direction the ray is travelling both numerically, g raphically, and
textually. The numeric value corresponds with the "CUR Angle" statistic. The gra phical method
shows the actual angle of the ray by projecting a straight line at the given ang le. And the textual
method is similar to the graphical method except a "/" is used if the signal is travelling upward
and a "\" is used if the signal is travelling downward. If the signal is horizon tal, a "-" is used.
This may be useful in some cases where the angle of elevation is too small to be reliably
depicted in the graphical display.
5.6 The Electron Density Graph and Numeric Density
The top-central panel of the ray-tracing display shows the electron density as t he signal
passes through the ionosphere. This is a very valuable tool not only as a diagno stic device, but
also as an analytical device. Using it, you can determine why signals may behave the way they
do, or what conditions exist to refract a ray in a certain manner.
Since electron density behaves in an exponential fashion, a logarithmic display is
necessary to graph changes in electron density. The electron density as a ray is being traced from
one point to another in the ionosphere is graphed on-screen using the same color that is used to
trace the ray itself. The base of the electron density graph begins at 1.0E+08 e lectrons per cubic
meter and increases to about 2.0E+12 electrons per cubic meter. The second logar ithmic division
86
is therefore at 1.0E+09 electrons per cubic meter, followed by 1.0E+10 electrons per cubic meter,
etc. Each subdivision is a tenth of a major division. That is, between 1.0E+10 a nd 1.0E+11, the
subdivisions represent a change of 1.0E+10 electrons per cubic meter.
The numeric density can also be read directly off the top-right-side textual pan el of the
ray-tracing screen. It is the sixth line down from the top line and is labelled "Ne" (which is short
for "electron density"). This value is given in scientific notation and represen ts the electron
density per cubic meter. Since there is only room for one digit in the exponent, and since the
electron density frequently exceeds values that require two digits for the expon ent, PROPLAB
converts the exponent into a value from 0 to 9 as usual. For exponents greater t han 9, letters are
used to define the exponent. The letter "A" represents 10, the letter "B" repres ents an exponent
of 11, and the letter "C" represents the exponent 12. For example, the reported electron density
of "4.6E+B" would be interpreted to read "4.6E+11" electrons per cubic meter.
5.7 Estimated Signal Strength Bar Graph
PROPLAB PRO Version 2.0 replaces the signal spreading loss bar graph with this n ew
estimated signal strength bar graph. This graph now shows the estimated strength of the signal
in units of decibels above one microvolt (or dBi). It is partially computed as the ray is being
traced through the ionosphere. The final value is determined when the ray actual ly reaches the
ground. For this reason, the signal strength bar-graph may jump around a bit as each ray is being
traced from one point to another. This is normal.
It is important to remember that the signal strength computed with this simple r ay-tracing
technique is subject to inaccuracies that cannot be accounted for with this simp ler ray-tracing
method. Use the comprehensive method for more accurate signal strength computati ons.
5.8 Signal Quality Bar Graph
IMPORTANT: PROPLAB PRO Version 2.0 uses a new signal-quality "measuring stick". This
was required because PROPLAB now computes estimated signal strengths as opposed to strict
quality figures derived from appropriate estimated models. This new measuring st ick attempts
to relate signal strength with signal quality and also considers other degrading parameters that
affect the quality of signals.
PROPLAB measures signal quality as a numerical value between 0 and 100. A value of
100 represents the best possible conditions (extremely good), while a value of z ero represents
complete signal loss or radio blackout conditions. PROPLAB converts the numerica l value to
a color-coded bar graph for easier interpretation. Areas within the blue region are associated with
very good to good propagation. Areas within the green section represent signal q ualities that may
vary from good to fair. The yellow section of the bar graph corresponds to signa ls that may vary
in quality from fair to poor. And signals that vary from poor to blackout condit ions occur within
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the red area of the bar graph.
The numerical value of the computed signal quality is also converted into a text ual
representation of signal quality. This textual representation is displayed on th e top-right panel
of the ray tracing screen to the left of the acronym "Sig Qual". The available q uality descriptions
are as follows:
VGOOD
VG-G
GOOD
G-F
FAIR
F-P
POOR
P-VP
BLKOUT
=
=
=
=
=
=
=
=
=
Very Good Quality
Very Good to Good
Good Signal Quality
Good to Fair Signal Quality
Fair Quality
Fair to Poor Signal Quality
Poor Quality
Poor to Very Poor
Radio Blackout (No Signal)
Using these tools of the ray-tracing screen, it is easy to determine signal qual ity levels as
the ray is being traced from one point to another.
If a ray is degraded to the point where the signal is blacked out, a large cross is stamped
on the screen at the precise location where the ray completely deteriorates and radio blackout
conditions are experienced. It is therefore easy to determine exactly where a si gnal dies in the
ionosphere.
There may be some instances where a signal cannot be completely traced through t he
ionosphere. For example, PROPLAB will abort tracing a signal through the ionosph ere if the
signal becomes engulfed in an area where the plasma frequency exceeds the operat ional
frequency of the signal. This can occur, for example, during transmissions that experience longhops through the ionosphere from a region of darkness into a region of light (su ch as might occur
during a darkness to sunrise transition). If the signal becomes trapped between the F-region and
the E-region (ie. within the E-layer valley region), an indefinite number of hop s will occur
between these two regions until the electron density either decreases and permit s the ray to
penetrate either of the layers, or the electron density increases and forces the signal to become
imaginary. It is this latter condition which forces PROPLAB to abort. If it occu rs (which should
be fairly rare), PROPLAB will impound the affect signal with a box.
Notice that the inability of PROPLAB to accurately trace rays through the ionosp here via
inter-layer reflections (as described above) is related to the simpler ray-traci ng technique
employed. The comprehensive ray-tracing method will accurately compute such effects. Hence,
rays are not impounded with boxes when using the comprehensive ray-tracing techn iques.
5.9 Magnetic Coordinates of the Ray
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The first two lines of the top-right panel of the ray-tracing screen show you th e magnetic
latitude and longitude of the ray as it is being traced through the ionosphere. This is a critical
parameter. Many of the functions and calculations used by PROPLAB depend on reli able
magnetic coordinates. For example, polar cap absorption begins to strongly affec t radiowave
propagation poleward of approximately 65 degrees magnetic latitude. PROPLAB uses an
accurate version of the Earth's magnetic field.
5.10 Solar Elevation Angle at the Ray Location
The third line of the top-right panel tells you the solar elevation ("Sol Elv.") , or the
elevation angle of the Sun above the horizon, at the current geographical coordi nates of the
travelling ray. This is a valuable number to watch. When the Sun falls below the horizon (at
sunset), this value will become negative. When the sun rises above the horizon ( at sunrise), this
value will become positive.
5.11 Height or Altitude of the Ray
As a ray travels through the ionosphere, the height of the ray is continually up dated beside
the acronym "Height" - located on the fifth line of the top-right panel of the r ay-tracing screen.
The given height is in kilometers.
5.12 Plasma Frequency at the Ray Height
The plasma frequency at the ray height is listed beside the "Plasma" variable in the topright panel of the ray-tracing screen (the seventh line down). The plasma freque ncy is given in
units of MHz.
5.13 Signal Elevation Angle
The angle of elevation used at the transmitter to broadcast the signal is given beside the
variable "Sig. Elev". It is given in units of degrees above the horizon. A zero degree elevation
angle therefore corresponds to a transmission directed at the flat horizon. An a ngle of 90 degrees
denotes a vertically propagated signal.
5.14 Auroral Zone Statistics
The three lines in the top-right panel of the ray-tracing screen labelled "Aur L AT", "Aur
LON", and "Aur Dist" describe the geographical position of that part of the equa torward edge
of the auroral zone closest to the travelling signal. The "Aur Dist" variable te lls you how far (in
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kilometers) the signal has spent inside of the auroral zone.
Signals that have not (or do not) pass through the auroral zone are associated w ith the
acronym "NoZone". As is inferred, this simply means that the signal does not pas s (or has not
yet passed) through the auroral zones. As the signal approaches an auroral zone, the "NoZone"
string will change to point to the geographical locations of the equatorward edg e of the auroral
zone that is closest to the signal. These variables are continually updated.
5.15 Ionospheric Distance Travelled
A radio signal typically does not suffer any significant degradation until after it penetrates
into the ionosphere. The distance travelled within the ionosphere (in kilometers ) is listed on the
last line of the top-right panel of the ray-tracing screen (by the variable "Ion o Dist"). This
distance does not include the distance required for the signal to travel from th e ground to the base
of the ionosphere. It only includes the distance travelled by the signal WITHIN the ionosphere.
5.16 Identifying the Receiver Location
When ray-tracing signals through the ionosphere, the location of the receiver is identified
by the dotted green line extending from the base of the distance grid to the top of the ionosphere.
It is similarly identified in the electron density graph (the top-central panel) as a dotted green
line. If the distance grid overlies the location of the receiver (effectively hi ding the location of
the dotted green line), the location of the receiver can be found by referencing the green arrow
directly below the distance-grid base.
It is important to remember that if your distance grid is not large enough to en compass
the receiver location, the dotted green line and the arrow may not be displayed on your screen.
To resolve this situation, increase the distance of the grid using the Options M enu of PROPLAB
described earlier.
5.17 Pausing and Skipping Traced Rays
You can force PROPLAB to pause anytime during the ray-tracing phase by pressing the
"P" (or Pause) key. To resume the ray tracing procedure, press any other key. Yo u can force
PROPLAB to skip tracing rays by pressing the "S" key while individual rays are b eing traced.
5.18 Aborting Ray Tracing and Saving Screen Images
To abort ray tracing, press the ESCape key anytime during the ray tracing proces s. Once
the ray tracing has been stopped (either by forcing it to abort or waiting for i t to complete), you
can save copies of the screen image to a GIF image file by pressing the "G" key. You can save
90
a copy of the screen image to a PostScript compatible file for sending to a lase r-printer by
pressing the "P" key.
5.19 Identifying Regions of Sporadic-E
Before tracing rays through the ionosphere, PROPLAB pre-examines the path signal s
travel to determine if any regions of sporadic-E are crossed. If regions of spor adic-E are crossed,
their exact locations are identified on the ray-tracing screen as red-colored re ctangular crosshatched regions between approximately 103 and 110 kilometers in height. Rays tha t intersect any
portion of these sporadic-E regions may be affected by the enhanced ionization i n these regions.
SECTION 6 - SIMPLE AREA COVERAGE MAPS
(Based on the Simple Ray-Tracing Technique)
One of the most impressive features of PROPLAB lies in its ability to produce br oadcast
coverage maps (also known as "area coverage maps"). Broadcast coverage maps are maps
showing the coverage, quality, or characteristics of signals that are broadcast by radio stations
(whether amateur or professional). PROPLAB combines the results of the simple ra y-tracing
technique results to produce broadcast coverage maps. This section shows you how this is done,
and how to interpret the results.
6.1 How are Broadcast Coverage Maps Constructed?
A radio transmitter cannot broadcast without some form of radiator. The radiator is the
antenna and the signal which enters the antenna is radiated outward in a directi on that is
dependent upon the type of antenna that is used. Antennas can be constructed to be exceptionally
directional in nature where narrow beams of radio signal energy are broadcast. O thers are
constructed to broadcast radio energy equally in all directions. These are calle d omni-directional
antennas. Before a broadcast coverage map can be generated, it is essential to k now the
approximate radiation pattern of the antenna being used to transmit or receive t he signals.
PROPLAB PRO Version 2.0 uses the currently selected antenna radiation pattern du ring
the ray-tracing phase. The broadcast coverage maps therefore take this into cons ideration.
Most antennas that are directional or semi-directional are designed to beam most of the
radio energy in specific directions. As well, all antennas broadcast radio energ y at optimum
91
angles of elevation. That is, most of the radio energy is beamed in preferred di rections and
angles of elevation. To create accurate broadcast maps, it is necessary to know:
1. The direction (or azimuth) of the transmission.
2. The azimuthal spread of the transmitted signal.
3. The useful elevation angle spread of the signal.
For example, let's assume that a directional antenna beams most of its energy in a 45 degree wide
azimuthal "swath". In that swath, most of the transmitted signal is directed upw ard at an
elevation angle between 4 and 30 degrees. These are the only quantities required for PROPLAB
to produce a broadcast coverage map.
PROPLAB produces a coverage map by ray tracing signals through the ionosphere us ing
small increments of the azimuthal spread and the elevation spread of the signal. In this way, it
is able to determine the broadcast coverage and quality of signals throughout th e range of the
transmitted signal.
For omni-directional antennas, you would use an azimuthal spread of 360 degrees, from
0 to 360, and an elevation spread of 90 degrees representing a transmitted signa l being broadcast
in equal intensity in all directions.
6.2 Beginning Inputs
The first prompt presented by PROPLAB is a question asking for which type of Bro adcast
Coverage Map to generate. To construct broadcast coverage maps from data collect ed using the
simple ray-tracing technique, select "S" at this prompt. To use the comprehensiv e broadcast
coverage mapping system (which uses the comprehensive ray-tracing technique), se lect "C".
Before any other inputs are requested, PROPLAB asks you if you want to use a
previously generated dataset. If you have previously computed a broadcast covera ge map and
simply want to view the results of the ray-tracings, you would select "Y"es at t his prompt. If you
respond "N"o, PROPLAB will delete any old pre-computed datasets and begin compil ing a new
one.
All broadcast coverage results are stored in the file "PATHS.OUT". If you want t o save
a broadcast coverage map dataset, rename this file to something else so that it is not truncated
and overwritten.
The first input required is the beginning azimuth of the transmission.
The second input required is the ending azimuth of the transmission. These two i nputs
define the limits of the antenna radiation pattern. For antennas which are semi- directional (ex.
those which transmit most of their power in one direction and smaller amounts of power in the
92
other directions), choose those directions where most of the energy is directed. The current
version of PROPLAB does not provide you with the ability to define radiation pat terns and
produce broadcast coverage maps based on those patterns. However, future version s will build
on this idea.
The third input defines the azimuthal step rate PROPLAB should use between the
beginning azimuth and the ending azimuth. Smaller step rates will result in grea ter spatial
resolution and better accuracy. However, smaller steps will also require more co mputation time.
Larger step rates provide quicker computation but less accuracy and the resultin g maps will
appear more "coarse".
The fourth input informs PROPLAB to ray-trace signals no further than the maximu m
distance specified. If the distance between a transmitter and a receiver is 6,00 0 kilometers, it
would be wise to specify a value approximately 2,000 kilometers beyond this poin t so that the
coverage does not end at the receiver location, but is extended beyond by 2,000 kilometers to
better define the characteristics of the transmission at those distances.
The next three inputs define the characteristics of the transmission in terms of elevation
angle. For example, if a directional antenna transmits most of its power from 4 to 30 degrees
in elevation, then a beginning angle of elevation of 4 degrees would be specifie d along with an
ending angle of 30 degrees. The third of these three inputs requires you to spec ify the elevation
angle stepping rate. Smaller step rates will result in finer spatial resolution (but again, longer
computation times). The elevation angle step rate is perhaps of greater importan ce than the
azimuthal stepping rate. An elevation angle step rate of 1 degree provides good resolution.
Smaller stepping rates can be used. There is no lower limit to the stepping rate , although a
stepping rate of zero obviously will not work.
Keep in mind that if PROPLAB is set up to ray trace with only one ground-hop, th en only
one ground-hop will be used when tracing rays through the ionosphere while gener ating broadcast
coverage maps. Before generating these maps, it is usually wise to set up PROPLA B so that it
will hop as many times as necessary to reach the destination distance. This can be done within
the Options Menu discussed earlier.
6.3 Computing the Required Data
After all of the required inputs have been given, PROPLAB begins the process of
computing the data required to build the broadcast coverage map. The time requir ed to compute
all of the data will depend on the values you used and the stepping rates employ ed. The time
may vary from only a few minutes to many hours, depending on the quality of the map you are
seeking.
PROPLAB begins the process of computing the data by ray tracing (with the simple raytracing technique) signals through the ionosphere using the starting azimuth and the starting angle
93
of elevation. After the first ray has been traced through the ionosphere to the destination (at the
maximum distance specified), PROPLAB increments the elevation angle by the eleva tion angle
stepping rate and traces a second ray through the ionosphere using the starting azimuth and the
new angle of elevation. This process is repeated until the last ray is traced re presenting the
ending angle of elevation for the starting azimuth. When this ray has been compl etely traced,
PROPLAB resets the angle of elevation back to the starting angle of elevation, a nd increments
the azimuth by the azimuthal step rate previously defined. PROPLAB then retraces all of the
rays from the starting angle of elevation to the ending angle of elevation at th e new incremented
azimuth and continues to reset the elevation angle and increment the azimuthal a ngle until the
ending azimuthal angle is reached. The process of computing the required data is then complete
when the last ray of the ending azimuthal angle and the ending elevation angle i s traced.
Following this, PROPLAB automatically transfers control over to the broadcast co verage map
generator subprogram known as "ANALYZE.EXE".
This entire process is time-consuming, but is accurate - and can be made as accu rate as
time permits using smaller angles of increments. The resulting data file (in "PA THS.OUT") may
be a respectably large file of many hundreds of thousands of bytes. There is no limit on the size
of the data file generated. PROPLAB will handle files from several K bytes to ma ny megabytes.
PROPLAB is only limited by the size of your hard-drive.
You can force PROPLAB to abort the computation of the data by pressing the ESCap e
key anytime during the ray-tracing phase.
This will force PROPLAB to load the
ANALYZE.EXE module. Premature abortion of this phase may result in inaccurate or
incomplete (or even perhaps non-existent or non-computable) maps due to insuffic ient data.
6.4 Types of Broadcast Coverage Maps Available
There are four types of broadcast coverage maps that PROPLAB will produce, after the
appropriate data has been computed and collected (see Section 6.3). PROPLAB will produce
maps of signal quality showing you the quality of signals throughout the broadca st range
specified. PROPLAB will also produce maps showing you the density of rays per un it area.
This latter function is valuable for determining the effects of ionospheric focu sing or defocusing
and therefore possible signal strength patterns. PROPLAB will also compute the t ime-delay of
the signal from the time it leaves the transmitter to the time it reaches the gr ound throughout the
broadcast coverage range and will produce maps showing the average time-delay pe r unit area.
Finally, PROPLAB will compute the multipath range of signals, or ranges of time required for
signals to reach specific regions. It will produce maps of multipath time-spread s, which is
exceptionally useful information for packet-radio systems or other digital-type communications.
Figure 6.1 is a sample broadcast coverage map showing signal quality from an omn idirectional antenna located in Colorado broadcasting over many thousands of kilo meters. The
image is of relatively poor quality due to the dithering that was required. Actu al final maps are
94
filled with color, not dithered. The key in the
center left and right sides of the figure define
what each of the colors mean. Unfortunately,
this is difficult to adequately discern in Figure
6.1, but shows you enough information for
our needs. Each individual color is associated
with a range of signal quality numerical
values ranging from 0 (blackout, or no signal
[NOSIG]) to 100, or extremely good signal
quality. Using this key, you can determine
the quality of signals anywhere on the map.
Some very useful information can be
derived from this map. For example, areas
where no signal is present are shown as areas
having no filled colors. The skip distance for
this example is easily defined as the inner circle-type boundary between no sign al and a strong
signal. Notice how the skip zone is elongated to the north and east away from th e transmitter
in Colorado. This is due to the failure of the ionosphere to reflect signals fro m the lower
ionospheric layers (E region, for example), perhaps brought about by the setting Sun. Signal
quality becomes very good just outside of the skip zone where MUF focusing is oc curring. Best
signal coverage occurs generally to the south and covers most of South America t o some degree.
Signals should also reach Hawaii, but with only fair signal quality. Paths more directly toward
the east and west (and northeast/northwest) become poor rapidly. On the frequenc y used to
produce this map, signals penetrate the ionosphere or are lost through other pro cesses fairly
rapidly with distance.
Figure 6.1: Dithered High-Quality Broadcast Coverage
Signal Quality Map
Best signal coverage (although not necessarily the best signal quality coverage) occurs
toward the south. As well, most of the continental U.S. is unable to receive the transmission due
to the size of the skip zone indicated. However, Florida and a portion of the ex treme
southeastern and eastern coastal states would receive an exceptionally good sign al since these
regions are just outside of the skip zone and are in the regions of high signal quality, as are
portions of the extreme northwestern states, northern British Columbia, and nort hwestern Canada.
Extreme southeastern and eastern regions of the U.S. that are almost directly on the skip-zone
boundary would also likely experience potentially severe fading caused by the cl ose proximity
of the skip-zone. This is known as MUF or skip fading and can result in very dee p fade-outs
followed by very strong fade-ins. Highest signal qualities for this scenario wou ld occur over
central America and southern Mexico - within the first-hop signal distance and o utside of the skip
zone. The signal deteriorates from there due to multi-hop propagation and associ ated absorption,
etc.
Although not shown here, a similar broadcast map showing the density of rays con verging
within certain regions would be useful for determining areas where ionospheric f ocusing or
defocusing may be occurring. Together with the signal quality map, it is possibl e to determine
95
where signal qualities correspond with ionospheric focusing to produce exception ally good
propagation conditions. Although ionospheric focusing may, in theory, increase s ignal strength,
you must keep in mind that signals may differ in total distance travelled to pro duce multi-path
types of distortion and decreased signal quality. For example, a two-hop signal may focus with
a one-hop signal to perhaps increase signal strength or produce destructive inte rference or even
beating between the two signals. In either of the two latter cases, signal disto rtion and fading
would be observed that might decrease signal quality even if the signal strength is increased.
For maps depicting the density of rays (focusing or defocusing), the values with in the key
indicate how many rays strike the ground within a specified binning distance (de scribed shortly).
Transmissions that are digital in nature may find the multipath ranging maps exc eptionally
useful. Digital transmissions are not as dependent upon the quality of a signal path as they are
upon the multipathing that is occurring over the path. Digital information canno t be transmitted
at high speeds if multipathing is occurring, because multipathing causes the pul ses (or packets)
of transmitted information to become entangled with each other and/or distorted into garbage.
Multipathing is what happens when one or more signals travel different paths to the same
destination. Each signal takes a specific amount of time to reach the destinatio n. For signals that
travel farther to reach a given destination, the signal will arrive at the desti nation sooner than a
signal that travels a shorter distance to the destination. The time difference b etween arriving
signals is what causes multipathing and is also what is responsible for limiting the speed and/or
quality of digital transmissions. For digital communications, paths with the low est possible
multipath ranges (or time-spreads of arriving signals) are desired. These areas typically tend to
occur near the maximum usable frequency, provided all of the signals are being r eflected from
a single ionospheric layer (this usually occurs near the MUF anyway).
PROPLAB will produce broadcast coverage maps of multipath ranging information
showing you the time-spread of signals (in milliseconds) anywhere within the bro adcast coverage
range specified. Voice communications can usually deal with fairly strong propag ation
multipathing before deteriorating to non-intelligibility. However, multipathing will degrade signal
quality by increasing distortion and fading. Multipath ranging maps may therefor e be useful to
help determine possible areas of distortion and fading.
After you have ray-traced the signals to produce the output dataset in the file
"PATHS.OUT", you can construct any of the four available maps without having to retrace rays.
The last map produced by PROPLAB is a simple map showing you the average time (i n
milliseconds) required for signals to travel from the transmitter to any point w ithin the broadcast
coverage range area. This is known as a propagation delay map.
6.5 Required Map-Generation Inputs
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PROPLAB first asks you whether you want to use a previously generated map or a f resh
map from the map library. If you have previously generated a broadcast coverage map and wish
to supplement it with additional information gathered by another ray-tracing run , select "S" to
use the previously generated broadcast coverage map. Alternatively, if you have previously
generated a map of maximum usable frequencies (etc), or a map showing the locati on of the
auroral ovals, sunrise/sunset grayline, sporadic-E, etc, you may use that map in stead of a fresh
map from the map library by selecting to use a previously "S"aved map. You there fore do not
need to use only a previously saved broadcast coverage map, but can use any map that was
previously saved by pressing the "S" key while the map was displayed on-screen.
If you choose to select a fresh map from the map library, the next menu shows yo u the
available maps in your map library and asks you to select one of those maps.
The next series of inputs defines the geographical location of the transmitter r esponsible
for the data in the file "PATHS.OUT". Type the geographical coordinates at the a ppropriate
prompts.
PROPLAB produces the broadcast coverage maps by binning the data into groups of
similar distances. For example, to determine the effects of ionospheric focusing and defocusing,
PROPLAB counts the number of individual rays that strike the ground within a spe cific area of
the transmitter. The default binning distance is 500 kilometers, so PROPLAB coun ts the number
of ground-striking rays within a 500 km zone. This zone is moved outward away fr om the
transmitter at a specific user-selectable "Stepping distance" rate, until the zo ne is at the maximum
distance previously defined when the broadcast map generation process was first started.
Following the input of the binning distance and the stepping distance rate, you are
presented with a menu and are asked to select the type of broadcast coverage map to generate
(signal quality, multipath ranging, etc). Choose whichever map you need to gener ate and press
ENTER to begin the process.
The time required to BEGIN drawing the map depends on the size of the dataset fi le
"PATHS.OUT", PROPLAB must first scan through the data and precompute various qua ntities
before the map drawing phase can begin. While PROPLAB is busy doing this, a box with
"Processing Data" will appear on your screen. Be patient. After PROPLAB has pre- scanned the
data, the map will be drawn on-screen, after which the geographical map showing the continents
and islands will be superimposed. After the map has been drawn, you are given ac cess to the
commands given in the following section.
6.6 Available Commands while Viewing Maps
PROPLAB will convert any of the graphical maps displayed into equivalent graphic image
files (or GIF images) by pressing the "G" key while the map is displayed. The sc reen can be
converted into a PostScript-compatible file that can later be sent to a laser-pr inter by pressing the
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"P" key. Screen images can also be saved to disk in a special format by pressing the "S" key.
This latter command permits you to integrate broadcast coverage maps in with oth er types of
maps. For example, after generating a broadcast coverage map, you can use the co ntouring
capabilities of PROPLAB to superimpose contours of maximum usable frequencies or critical
frequencies, etc, on the broadcast coverage map. Resulting maps may be invaluabl e and provide,
for example, the broadcast coverage signal quality along with contours of maximu m usable
frequencies, solar zenith angles, and any other information that may be helpful to interpret the
quality of signals within the broadcast coverage of the transmission.
PROPLAB does not normally provide a key defining what each of the colors mean in the
broadcast coverage map. To display the key, press the "L" key on your keyboard. The meaning
of each of the colors will then be displayed on-screen.
If you are not interested in saving the screen image, press any other key and PR OPLAB
will either return you to the DOS prompt (if you began running ANALYZE from the DOS
prompt), or will return you back to PROPLAB's Main Menu.
SECTION 7 - COMBINING MAPS
Once you have become more familiar with the general functions and operation of
PROPLAB, you may begin tapping into a few of the more powerful features of PROPL AB, such
as combining maps.
PROPLAB is capable of presenting its results using a variety of different map pr ojections.
The ability to combine maps magnifies the usefulness of the software by many mag nitudes by
making it possible to present a great deal of information on-screen at once.
For example, during a geomagnetic storm, the location of the auroral zones expan d
equatorward, affecting signal paths in the middle latitude regions. As well, sig nal qualities
decrease and multipathing may increase. Signals may also be affected by sporadic -E. Maximum
usable frequencies will decrease. PROPLAB provides you with all of the tools req uired to fully
analyze all of these quantities. It will produce maps showing you the location o f the auroral
ovals, the location of sporadic-E, the path travelled between the transmitter an d receiver, as well
as maps showing maximum usable frequencies and signal qualities. However, all of this
information is not available on a single map. You would normally have to generat e each map
for each quantity separately and then reference each separate map individually. PROPLAB gives
you the power to combine maps or superimpose data onto previously constructed ma ps.
Each time a graphical image is displayed (with the exception of the ray-tracing screen),
you have the option of pressing the "S" key to Save the graphical screen image i n a special
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format to disk. This is the key to combining maps. Every time an application run s that may
result in a generated map, the question is first posed: do you want to use a pre viously generated
map or a map from the map library? To use a map that has been previously saved i n the special
format, choose the option to use a previously generated map. That application wi ll then use the
map saved to disk in the special format instead of pulling out a fresh map from the map library.
This is the process used to combine maps.
Let's say you want to generate a broadcast coverage map showing you the quality of
signals within the broadcast area as well as global maximum usable frequencies f or a 4,000
kilometer path. Your first step would be to generate the broadcast coverage map using the
material presented in Section 6. This would involve a fair amount of ray-tracing activity. After
that process completed, you would create the actual broadcast coverage map. When this map is
finished being drawn, press the "S" key to save that screen image to the special disk format, then
return to PROPLAB's Main Menu. Next, select the option to generate global ionosp heric maps.
After this subprogram has been loaded, you will again be presented with the ques tion of whether
or not to use a previously generated map. Inform the application to use the prev iously generated
broadcast coverage map that was saved by pressing the "S" key. PROPLAB will then
automatically place that saved screen image on-screen and will superimpose all m aximum usable
frequency contours for 4,000 kilometer distances on that broadcast coverage map. The resulting
product is a map combining the broadcast coverage map with the maximum usable fr equency
contour map.
While this combined map is on-screen, you can press the "S" key again to save th at map
to disk in the special format and use that map for superimposing other material upon. For
example, you could superimpose contours of solar zenith angles on the combinatio n broadcast
coverage and MUF map previously generated. This time, you may want to choose a d ifferent
color for the solar-zenith angle contours so that the solar zenith angle contour s can be
differentiated from the MUF contours. Many maps of different types can therefore be
superimposed on one another to provide a wealth of information on one screen.
SECTION 8 - ALL-BAND SPECTRUM ANALYSIS
(Using the Simple Ray-Tracing Technique)
PROPLAB comes with a powerful new function to produce oblique sounding ionograms ,
giving you the ability to analyze propagation characteristics and conditions thr oughout a wide
range of frequencies. This function is imbedded within the Simple Ray Tracing su bmenu and
can be found by selecting Main Menu option 1,"S", submenu option 4. The followin g discussion
pertains strictly to this function.
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8.1 What is an Oblique Sounding Ionogram?
Ionograms are produced using an instrument known as an ionosonde. Ionosondes are
simply special radio transceivers (radio transmitter/receiver combination) desig ned to transmit
signals into the ionosphere and measure the character of the energy that is retu rned from the
ionosphere. In this respect, they are similar to radar guns.
We established earlier that signals which are propagated into the ionosphere are reflected
according to the density of electrons present in the ionosphere. Regions of high ionospheric
electron density are capable of returning higher frequencies. This behaviour is the foundation
upon which we are able to probe the ionosphere.
Ionosondes probe into the ionosphere by using a sweep-frequency transmitter. Tha t is,
the frequency of the transmission is swept (or increased) from low frequencies t o high
frequencies. As the signals from the low frequencies penetrate the ionosphere, t hey are reflected
back to the transmitter and the receiver picks up these reflected transmissions. Since low
frequencies can be reflected by relatively low electron densities, these low-fre quency reflections
give us an idea of the content of the lower portion of the ionosphere. As the fr equency of the
transmitter increases, the signals penetrate deeper into the ionosphere before t hey are returned to
the Earth. Eventually, as the frequency continues to increase, the frequency wil l exceed the
critical frequency of the F2 layer and never return to the Earth. By carefully t racking all received
signals with the receiver as the transmitter frequency is increased, we can buil d a "picture" of the
ionosphere up to the maximum density of the F2 layer.
These "pictures" are known as
ionograms, and can give you a wealth of information regarding the state of the i onosphere.
Oblique ionograms are simply pictures of the ionosphere produced by measuring al l of
the received energy propagated from a transmitter some distance away, as the fre quency of the
transmitter is swept from low to high frequencies. Using oblique ionograms, you can easily
determine optimum working frequencies, maximum usable frequencies, minimum usabl e
frequencies, the extent of signal multipathing present on specific frequencies, and much more.
We will discuss the proper interpretation of these features shortly.
PROPLAB produces oblique sounding ionograms between two points by sweeping the H F
spectrum at the transmitter and measuring the signals that reach the desired rec eiver. The process
is rather complex and can be time-consuming for detailed results, but the inform ation which can
be gathered from such an analysis is well worth the time.
8.2 Phase 1: Collecting the Required Data
There are two phases to producing Oblique Ionograms with PROPLAB. The first phas e
is to collect the data. The second step is the analysis phase, which is discusse d in Section 8.3.
This first data-collection phase requires the most time, but is extremely simple to set up.
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First, you must make certain that the transmitter and receiver locations and par ameters are
properly established (using option 8 of the Main Menu). Be sure that the relativ e transmitter
power is set properly, as well as the geomagnetic A-index and the sunspot number or solar flux.
Also be certain that the date and time (local or UTC) is also properly entered. These are the
most critical parameters.
If sporadic-E may affect the signal path, make sure you use option 3 of the Main Menu
to set-up the regions of sporadic-E. If solar flares or PCA might inhibit commun ications, enter
the appropriate data in option 8 of the Main Menu.
Make sure that all of the items in option 8 of the Main Menu are properly establ ished for
the signal path you wish to analyze, then select option 1 of the Main Menu to en ter the RayTracing menu. Follow this by selecting suboption 4 (Generate Oblique Sounding Io nogram) of
the Ray-Tracing menu.
You will be asked whether you want to analyze previously generated ionogram data . If
you have previously collected data, you can skip the data-collection phase and g o straight to the
analysis phase by typing "Y" (Yes) at this prompt. If you do not want to analyze a previously
collected dataset, type "N" (No).
You will now be asked whether you want to append collected data to the existing
ionogram database. If you previously collected data, but want to extend the data to improve the
accuracy of the results, you will want to select "Y" to append all collected dat a to the existing
database. If this is your first data-collection run (or if you are beginning to collect data on a
different signal path), then select "N" so that any existing data is truncated.
A paragraph of information is next displayed which should be entirely read. It s imply
explains what is about to happen and how to respond to the following prompts.
The series of prompts that follow specify details of the transmission, the frequ encies to
use, and step rates. The first three prompts define the antenna radiation patter n of the transmitter
(beginning angle of elevation, ending angle of elevation, and the step rate to u se when raytracing). An omni-directional antenna transmits power into space approximately e qually in all
directions. We only consider the vertical elevation above the horizon since the antenna is
assumed to already be pointing at an optimal azimuthal location toward the recei ver. An omnidirectional transmitter would have a starting elevation angle of 0.0 degrees, an d an ending angle
of elevation of say 89 degrees. Avoid using ending elevation angles of 90 degrees, as the nearvertical propagation of low-frequency signals may result in lengthy computation times during this
phase. Values close to 90 degrees can be used instead, such as 89.0 or 89.5. After inp utting the
starting and ending elevation angles of the transmission, you are prompted for t he elevation angle
step rate. Since PROPLAB traces rays through the ionosphere from the starting el evation angle
to the ending elevation angle, a step rate must be specified so that PROPLAB kno ws how to
progress from the starting to ending angles. The lower the step rate, the greate r the resulting
accuracy will be, but the longer the computation time will also be. A step rate of 0.5 degrees
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to 1.0 degree yields reasonable accuracy.
The prompt asking to "Update the Screen Statistics at what rate" does not affect the
accuracy of the results, but will affect the speed that PROPLAB produces results . This prompt
determines how frequently PROPLAB should update the ray-tracing screen statistic s. Large
values (in excess of say 200 to 300) will speed up the ray-tracing slightly by u pdating the
statistics section of the screen less frequently. If you like to keep close tabs on the statistics, then
use a lower value.
The final three prompts deal with how the transmitter frequency is to be varied. You are
asked to type in the starting frequency, the ending frequency, and the frequency step rate to use
during the ray-tracing phase. To analyze propagation conditions between the tran smitter and
receiver between 1.0 MHz and 40 MHz, use a starting frequency of 1.0 MHz and an ending
frequency of 40.0 MHz. The step rate you use here will determine the resolution of the results.
For high-resolution, use low step increments of say 0.25 MHz or less. For faster computation
and low-resolution results, use step rates of 0.5 to 1.0 MHz. Keep in mind that as the step rate
is increased, the resolution of the results will decrease, making it harder to s ee perhaps smaller
features in the ionogram and perhaps decreasing the accuracy of the results in t he process.
After you have responded to these prompts, PROPLAB begins collecting the necessa ry
data by rigorously ray-tracing through the ionosphere from the transmitter to th e receiver,
sweeping both the transmitter frequency and the elevation angle of the transmiss ion.
You can halt the data-collection phase at any time by pressing the ESCape key. W rite
down the current frequency and elevation angle being ray-traced before aborting so you can
continue the processing from that point later, if you desire, by appending the f uture collected data
to the database of results.
8.3 Phase 2: Analyzing the Results
After PROPLAB has finished the data-collection phase, the utility program
"SOUNDER.EXE" is loaded and executed. This utility reads the results from the da tabase file
"CHIRP.OUT", processes the data, and displays the results on-screen. This utilit y can be
optionally run from the DOS command-line after the database has been built.
Provided the database file "CHIRP.OUT" exists and contains data, PROPLAB will di splay
the geographical location of the receiver as well as the great-circle distance t o the receiver, and
ask you if you want to change the location of the receiver. Since PROPLAB ray-tr aces through
the ionosphere, a profile of propagation conditions can actually be computed any where between
the transmitter and receiver, provided the chosen location lies along the same g reat-circle path.
If you choose to change the location of the receiver, you will be asked to type in a new greatcircle distance to the receiver. This distance is then later converted into appr opriate geographical
coordinates and are displayed along with the final results. You cannot specify a new receiver
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location beyond the distance of the receiver used during the ray-tracing phase.
between the transmitter and the receiver.
It must lie
If you do not wish to alter the location of the receiver, press ENTER or type "N " and
press ENTER. This will give you the second prompt which asks you to accept signa ls that reach
the ground within +/- how many kilometers of the receiver. In other words, it as ks you to
specify how closely signals must approach the receiver location before they are accepted as
having actually reached the receiver. This is an important prompt and deserves f urther
explanation.
In reality, radio transmissions are composed of an infinite number of "rays" tha t travel
individually through the ionosphere. As a result, the reflected radio energy hit s the ground at an
infinite number of points along the great-circle path towards the receiver. You can therefore
sample almost any location along the great-circle path and measure signal energy reaching the
ground. The same does not apply to PROPLAB. Since PROPLAB must individually trac e each
ray through the ionosphere, it is not practical to permit an infinite number of rays. To speed up
the procedure, it is necessary to limit the number of rays that are traced throu gh the ionosphere.
If a significant number of rays are traced, the results will be similar to what would be expected
in a realistic situation where an infinite number of rays are used. If a smaller number of rays are
used, there may be gaps along the great-circle path where no rays reach the grou nd. In order to
build an oblique ionogram, the receiver must receive energy from the transmitter . But if a
smaller number of rays are used, it is possible that none of the propagated rays will EXACTLY
reach the receiver. Several rays may straddle the receiver, hitting the ground p erhaps only a few
tenths of a kilometer or a few kilometers from the receiver location. To solve t his situation, we
must assume that each transmitted ray represents many individual rays with sligh tly differing
characteristics (slightly different elevation angle of transmission, slightly di fferent frequency, etc).
If we make this assumption (which is true enough), we can expect that for each t raced ray which
hits a specific location, there will be an infinite number of imaginary rays whi ch strike the ground
at slightly differing locations from the principal traced ray. All will strike t he ground a few
tenths of a kilometer or a few kilometers on either side of the traced ray, effe ctively eliminating
all gaps present.
If we use this theory and reasoning, then this prompt makes sense. We are, in es sence,
saying that if a traced ray strikes the ground within say +/- 50 kilometers of t he receiver, then
an associated imaginary ray has actually arrived at the receiving antenna with c haracteristics close
enough to the traced ray that the two rays (the imaginary ray and the traced ray ) can be
considered the same. As a result, all rays that reach the ground within +/- 50 k ilometers of the
receiver are assumed to have been received by the receiving antenna and are proc essed.
If you collected data using relatively large step increments, there will be rela tively few
traced rays, implying that each ray must be associated with an infinite number o f imaginary rays
that have more substantial differences or vary in characteristics more seriously than the traced
ray. Each traced ray must therefore be assumed to cover a larger area of ground in order to
simulate true conditions realistically. As a result, if there are a relatively s mall number of traced
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rays that are used, you may have to accept signals that strike the ground within a larger area than
just 50 kilometers. You might need to accept signals within +/- 200 kilometers o f the receiver.
For very large numbers of rays, the concentration of rays that strike the ground along the greatcircle path will be sufficient to use smaller values, say within +/- 5 or 10 kil ometers of the
receiver. You can experiment with the values, but keep in mind that you want to keep this
window as small as possible while still retaining a respectable number of sample s to build
reliable results.
The next prompt asks you whether you want to analyze all rays regardless of thei r signal
quality. In most cases, you will want to consider only those rays that are assoc iated with a signal
quality above zero - in other words, one which has not "blacked-out" due to abso rption or other
factors. This filters out all of the signals that would not be received because they have been
degraded to the point of uselessness and displays only those signals that you sh ould be able to
"hear" at the receiver. If you're curious about the character of those signals t hat never reach you,
you can specify "Y" at this prompt to accept all signals that reach the receiver , whether they are
useless or not.
The last major prompt asks you for the type of analysis you want to carry out: a n analysis
of propagation delays (by pressing "P"), or an analysis of elevation angles (by pressing "E"). The
propagation delay analysis shows you how long it takes the received signals to r each the receiver,
after they leave the transmitting antenna. The results given by this analysis ar e far-reaching and
exceptionally useful. The elevation-angle analysis shows you what transmission e levation angle
was used for each of the signals that were received by the receiving antenna. Th is plot is
likewise, a very useful tool and can give you a great deal of insight into optim um transmission
angles. We will discuss the features of these plots shortly.
If you produce a propagation-delay plot, you will be asked if you want the compu ter to
automatically compute the resolution of the display, or if you want to control t his yourself. Press
ENTER or type "Y" to have the computer do this for you automatically. To set the resolution
manually, you are asked for one final piece of information: how many millisecond s should the
grid display? A single-hop E-region reflected signal requires a little more than approximately
3 milliseconds to travel from the transmitter to the ionosphere and back to the ground. A twohop E-region reflected signal will likewise require twice that time. An F-region reflected signal
may take a range of differing times, depending on how deeply the signal passes i nto the
ionosphere, the frequency used, etc. In most cases, a value of 4 milliseconds wi ll be more than
adequate and may produce a more realistic (similar to an actual ionogram) result than an autocomputed value. But if you're unsure, let the computer do the work for you.
If you produce an elevation-angle related plot, you will be asked two final ques tions
before the data is finally processed. You will be asked to type in the minimum e levation angle
used during the ray-tracing phase, and the maximum elevation angle used during t he ray-tracing
phase. These values determine the grid size.
After you have answered all of the prompts, PROPLAB begins processing the databa se
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of information contained in "CHIRPS.OUT". You will be told to please wait as the data is
processed. After the data is processed, the results are displayed on-screen.
8.3.1 The Propagation-Delay Plot
Figure 8.1 shows a sample
propagation-delay plot produced over the path
from Hawaii to Colorado. The transmitter
was located at Hawaii. The analysis was
produced for June 30, 1994 at 15:00 UTC
during geomagnetically quiet conditions. This
corresponded to the declining phase of solar
cycle 22 and as a result was associated with
a relatively low sunspot number of about 30.
The lower panel of this figure shows
you how long it took signals to reach
Colorado from the Hawaiian transmitter, in
milliseconds. Each plotted block represents Figure 8.1: Oblique Sounding Propagation-Delay
one traced ray which hit the ground within the Ionogram from Hawaii to Colorado on 30 June 1994 at
05:00 UTC during geomagnetically quiet conditions.
specified acceptable distance from the
receiver. Although this figure does not show
it, the full-color display produced by PROPLAB plots each block using a specific color that
corresponds to the number of hops that was required for the signal to reach the receiver. Since
the display in Figure 8.1 is black and white, we have grouped those rays which h ave common
numbers of hops. At the extreme upper left coroner of the figure, a Key exists w hich (on fullcolor displays) shows you what plotted colors correspond to certain numbers of h ops. Notice that
there were no signals that arrived at the receiver using a single hop. At least two hops were
required to traverse the 5,300 kilometer path from Hawaii to Colorado.
The frequency separation grid lines shown in Figure 8.1 require further explanat ion. Each
labelled frequency (ex. 9.6 MHz) is associated with a bright WHITE vertical line (which is not
discernable in the black and white rendition of this figure). At each whole numb ered frequency
(8.0, 9.0, 10.0, 11.0 MHz, etc), a LIGHT GRAY vertical line is plotted. For this reason, some
lines may appear irregularly spaced in the frequency grid for the figures which have been
reproduced here. However, while running PROPLAB, they are easily discerned from one
another.
The upper panel of Figure 8.1 describes the estimated signal quality. Please note that the
given signal quality is not to be taken as an absolute. The computed signal qual ity is simply the
average signal quality of all rays that arrive at specific frequencies. They do
not take into
consideration effects of strong multipathing, ionospheric focusing, etc. For the se reasons, the
given signal quality should be used as an estimate only and a guide to the gener al quality of
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signals that can be expected. We will improve the quality computation figures in future releases.
Figure 8.1 shows that five modes of propagation are possible between Hawaii and
Colorado on the high-frequency bands: 2 hop mode, 3 hop mode, etc, to the 6 hop mode. The
lower the frequency, the more modes that are supported. A greater number of mode s can have
advantages over single-mode communication in that should one mode fail, other mo des still exist
to receive the signals on. However, larger numbers of modes (or hops) increase t he multipathing,
or the time-spread between received signals. Multipathing creates signal distort ion since there
may be several signals from the transmitter arriving at the receiver at slightly different times.
This can cause destructive interference, distortion, beating between the signals , and strong to
severe fading. But for many types of communications, these types of signal degra dation might
not seriously impede the intelligibility of signals (for example, CW communicati ons). Other
types of communications (digital) can be rendered useless with multipathing.
In Figure 8.1, there is almost a 3 millisecond range in reception times for sign als arriving
at Colorado from Hawaii. There is also a great deal of overlapping between signa ls of various
types of modes. For example, at 7.1 MHz, there exist three modes of propagation: 3-hop, 4-hop,
and 5-hop paths. This is determined by scanning the graph vertically from the 7. 1 MHz grid line
and examining all those signals of differing colors that arrive at the receiver. In this example,
there were three rays received at this frequency at approximately 18.4 milliseco nds (ms), 19 ms,
and 19.75 ms. The time spread is therefore (19.75 - 18.4) about 1.35 ms between the slowest
and fastest arriving signals. This is a tolerable time-delay for voice-based com munications and
is not too bad for digital communications either. The maximum rate (in bits per second) of
digital communications is approximately equal to the reciprocal of the range of multipath
propagation times. In this example then, digital communications might be support ed on 7.1 MHz
at a maximum rate of approximately (1 / 0.00135) 741 bits per second, or about 7 4 baud. Note
that this analysis is based on the data collected to form Figure 8.1. The accura cy of the
assessment is therefore dependent on the amount of data collected.
From Figure 8.1, the highest signal qualities appear to be associated with the 2 -hop mode
of communications. This is primarily the result of reduced distortion from low m ultipathing and
relatively low signal degradation. There are two regions where no signals were o bserved. This
void exists at about 14.0 to 14.5 MHz and again near 16.75 MHz. Signals from Haw aii at
frequencies near these voids would not be received at Colorado.
The maximum usable frequency (MUF) from Hawaii to Colorado is easily determined
from Figure 8.1. The MUF is about 17.5 MHz. This is a realistic MUF value that s urpasses the
accuracy of the MUF-computations available at PROPLAB's Main Menu Option #2. Why are
these MUFs more accurate for paths greater than 4,000 kilometers? PROPLAB comput es the
MUF in Main Menu Option #2 by computing the MUF at two control-points approximat ely 2,000
kilometers away from the transmitter and receiver. It then selects the lower of these two MUFs.
PROPLAB does not rigorously ray-trace through the entire length of the path when computing
long-distance MUFs. Nor does it consider effects of sporadic-E on the MUF. The o bliqueionogram technique used to produce Figure 8.1 does rigorously ray-trace througho ut the entire
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length of the path. It makes no assumptions or estimations by limiting the analy sis to two control
points. And it will consider the effects of sporadic-E on the MUF. For this reas on, you can
determine actual MUFs between any transmitter or receiver using these plots.
It is possible to reanalyze propagation conditions at any distance between the t ransmitter
and receiver by changing the location of the receiver when so asked. The first q uestion posed
by the PROPLAB Oblique Sounder Ionogram utility (SOUNDER.EXE) is "Change Receive r
Location?". By responding to this question with "Y", you are asked to type in a new distance
to the receiver.
Figure 8.2 shows the results of a reanalysis between Hawaii and a point at about 36N
126W, off the California coast. This was done by changing the distance between t he transmitter
and receiver from 5,300 kilometers to 3,500 kilometers. Notice that we are still analyzing
conditions along the same great-circle path, but at a different distance from th e transmitter.
The results shown in Figure 8.2 differ
substantially from those depicted in Figure
8.1. First, notice the increase in the MUF to
about 23.5 MHz, made possible by the ability
of the ionosphere to return single-hop signals
from a portion of the ionosphere that is more
intensely ionized. At 05:00 UTC on 30 June,
Hawaii is almost directly on the sunset
grayline. As the signal travels from Hawaii to
36N 126W (towards Colorado), the electron
density in the ionosphere will decrease
because the signal is moving into deeper areas
of the night. The 5,300 kilometer path
Figure 8.2: Propagation-Delay Ionogram from Hawaii to
requires two hops. The first hop would have
36N 126W made from the same data as Figure 8.1 by
been associated with an MUF near 23 MHz,
changing the distance from 5,300 km to 3,500 km.
but the second hop would be associated with
an MUF closer to 17.5 MHz.
Higherfrequency signals would penetrate the ionosphere due to the decreased night-time electron density
present at the second-hop location. For this reason, the MUF for the 3,500 kilom eter path to 36N
126W is higher than the MUF for the path to Colorado.
Notice also that the various modes of communication are better defined in Figure 8.2.
There are also a greater number of rays received throughout the frequency range plotted, which
improves the visibility of certain features in the plot. The overall signal qual ity is also higher.
Referring to Figure 8.2, you can determine the MUF for signals of any number of specific
hops. For example, it was already shown that the 1-hop MUF was about 23.5 MHz. S imilarly,
by examining the maximum frequency on the ionogram in Figure 8.2 for 2-hop signa ls, it can
be seen that the 2-hop MUF is about 15.25 MHz. Similarly, 3-hop signals are asso ciated with
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an MUF of about 11.5 MHz, 4-hop signals with an MUF of 9.5 MHz, 5-hop paths with an MUF
of 5.25 MHz, and 6-hop paths with an MUF of about 2.75 MHz. Since signals are us ually
focused and become stronger near the MUF, you can expect signals with multi-hop MUFs to be
stronger than might normally be expected. However, signals which have multiple g round hops
also lose signal strength due to ground absorption and multiple ionospheric cros sings, they might
therefore be weaker than single-hop signals.
With this information in mind, consider what communications might be like along the
3,500 km path depicted in Figure 8.2 from Hawaii to a ship off the California co ast near 36N
126W on 11.5 MHz. First, determine what modes of propagation are possible on thi s frequency
by scanning vertically up from the 11.5 MHz grid region. There are three modes o f
communication possible on this frequency: 1-hop, 2-hop, and 3-hop modes of commu nication.
The signal strength depicted in the upper panel of the figure suggests "fair" si gnal quality should
exist on this frequency. Signals requiring only one hop will likely have fairly strong signals.
However, a strong signal can be associated with poor quality if multipathing is a factor. And in
this case, multipathing will play a part in determining signal quality. Signals that require 2-hops
before reaching the receiver will have slightly less signal strength than single hop signals, and
will be out of phase with the stronger single-hop signals by about 0.5 milliseco nds. This is a
fairly small time-spread and will not significantly degrade communications, but may contribute
to a slightly "fuzzy" level of voice communications. Now consider the final mode of
communications, the 3-hop mode. Notice that our 11.5 MHz frequency lies on-top o f the MUF
for 3-hop paths. As a result, the signal strength of the 3-hop signals may be st ronger than we
might otherwise anticipate. In addition, these signals will require an additiona l 1.5 milliseconds
from the time the single-hop signals arrive, before they reach the receiver. Thi s will introduce
additional and more serious distortion into the received waveforms, degrading th e received signal
a bit more. In this case, the given signal quality may in actuality be close to "fair" on 11.5 MHz.
Notice how the quality suddenly improves (goes to higher numbers) as soon as the MUF
for 3-hop signals is passed. At 12.0 MHz, the signal quality jumps up to "good" values,
primarily because the additional distortion introduced by the 3-hop signals is n o longer present.
Only 2-modes of propagation are possible at 12.0 MHz: single hop and dual hop co mmunication
modes. The relatively small multipathing (0.5 ms) that exists between the 1-hop and 2-hop
signals is (in this case) negligible. It is interesting to note that the decreas e in propagation delay
time-spread between 11.5 MHz (1.5 milliseconds) and 12.0 MHz (0.5 milliseconds) would have
a significant impact on the maximum speed of digital communicators. In this inst ance, the
reduction in multipathing would increase the maximum speed of digital communicat ions by about
a factor of 3, simply by judiciously choosing low-multipath frequencies. This il lustrates a small
portion of the value of performing an oblique-ionogram type of signal path study .
Figure 8.2 still shows a region where no signals were received near 15.0 to 15.5 MHz.
Notice that the void in the frequency spectrum has increased in frequency from F igure 8.1 (where
it resided between about 14.0 and 14.5 MHz) to Figure 8.2. The fact that this re gion of
"blackness" in the frequency spectrum was also evident in the 5,300 kilometer pl ot in Figure 8.1
suggests that the anomaly is in all likelihood real and should be avoided. We co uld not be so
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certain of this if the density of traced rays (during the data-collection phase) was low. In these
examples, a sufficient number of rays were traced to produce reasonably realisti c and accurate
results.
8.3.2 Elevation Angle Plots
Figure 8.3 is a plot of elevation angles
with frequency, as opposed to propagation
delay time with frequency. It was derived
from exactly the same data as Figure 8.2 for
the 3,500 km path from Hawaii to the ship at
36N 126W.
In a nutshell, this plot shows you what
transmission angles of elevation are required
for signals to reach the receiver at 36N 126W
on specific frequencies throughout the HF
spectrum. It is an extremely valuable tool for
determining optimum transmission takeoff
angles to remote locations.
Figure 8.3: Elevation Angle Ionogram from Hawaii to
36N 126W (3,500 km). Compare with Figure 8.2.
Again, these black and white figures
are actually full-color on your monitor, and each of the plotted lines are color -coded so you can
easily determine what plotted lines are associated with specific numbers of grou nd hops. The
Key in the upper-left-hand corner of the screen defines how many hops each of th e colors
represent. The angle of elevations can be read off of the vertical grid from top to bottom on the
far left of the screen, where the propagation delay times were formerly determin ed in the last
section.
In order to make optimum use of the ionosphere, it is necessary to orient your a ntenna
so that most of the radiated power is transmitted at specific angles of elevatio n. Failure to do
so limits how much control you have over where and how far your signals travel. In order for
a signal to reach the ship at 36N 126W from Hawaii, it will be necessary to use one or more of
the transmission angles of elevation shown in Figure 8.3.
Some people might have problems understanding how to read the plot in Figure 8.3 . To
help in this regard, let's examine the single-hop line in Figure 8.3. This long plotted line covers
frequencies from about 7 MHz up to the MUF of 23.5 MHz. It tells you that for si ngle-hop
paths, very low radiation angles of elevation between 0.0 and 3.0 degrees are re quired for signals
to reach the ship at 36N 126W. In addition, there is a gap or void where no sign als will be
received (from one-hop signals), even with low-angles of elevation between about 14.25 and 16
MHz. Two-hop signals can only be received if the angle of elevation at the trans mitter is
between about 11 and 17 degrees above the horizon. Notice how only two-hop signa ls will be
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received between 14.25 and 15.25 MHz, as these are the only traces present. Betw een 15.25
MHz and 16.0 MHz, no signals are receivable at the ship. Both single-hop and dua l-hop paths
fail to reach the transmitter between these frequencies.
With this information in hand, you can determine what angles of elevation to use to
exploit communications to remote locations using specific numbers of hops. You c an also
determine to some degree what type of antenna radiation pattern should be used. For example,
for reliable single-hop communications, a very directional and narrow beam anten na will be
required so that most of the radiated energy is emitted at angles of elevation l ess than about 4
or 5 degrees. Since most antennas in use today have a broader radiation pattern, it is reasonable
to think that a fair amount of energy will be lost if only radiation angles betw een about 0 and
3 degrees reach the desired receiver in one hop. Such antennas are also more exp ensive and a
bit more difficult to build. It might therefore be to your advantage to concentr ate on 2-hop paths
to the receiver, where the range of elevation angles required to reach the recei ver are not as tight.
Using this information, you can construct antennas that avoid undue multipathing effects.
For example, if an antenna was constructed to transmit most of its radiated powe r between
elevation angles of 5 and 18 degrees, most of the radiated power would reach the receiver in 2hops. The narrow transmission angles used would eliminate most of the multipathi ng interference
that might occur with the single-hop, 3-hop, 4-hop, and 5-hop propagation modes, resulting in
improved signal quality at the receiver.
Another way to use this information is to analyze how much multipathing might oc cur
on specific frequencies with a given antenna. For example, an antenna that trans mits most of its
power between 10 and 30 degrees would see up to 3 propagation modes: 2-hop, 3-ho p, and 4-hop
propagation modes. To reduce multipathing effects and distortion, Figure 8.3 sug gests that
frequencies between 11.75 and 15.25 MHz should be optimum. The 3 and 4-hop MUFs are
surpassed at 11.75 MHz and are no longer a problem, reducing multipathing substa ntially and
improving signal quality. The 15.25 MHz upper-limit defines the 2-hop MUF. Frequ encies
above 15.25 MHz therefore will penetrate the ionosphere before reaching the rece iver. Singlehop signals are not possible because the angles of elevation required to reach t he receiver using
the single-hop mode of propagation are not within the radiation pattern of the t ransmitting
antenna. For these reasons, the 2-hop propagation mode is the desired mode for t his antenna,
path, and time of day.
Figure 8.4 is a similar elevation angle plot for the 5,300 kilometer path from H awaii to
Colorado. It was constructed using exactly the same data that was used to produc e the plot in
Figure 8.1. Also compare it with the shorter 3,500 kilometer path in Figure 8.3 and note the
differences. Perhaps the most pronounced is the observation that lower angles of elevation
produce more hops to the destination than for shorter distances. As well, the ra nge of elevation
angles required to support say six modes of propagation decrease as distance inc reases. For
example, a radiation elevation angle pattern of 30 degrees is required to encomp ass all six
possible modes of propagation on the 5,300 kilometer path, while the 3,500 kilom eter path
required a 42 degree elevation angle spread to cover six modes of propagation. T he elevation
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angle spread between individual modes
decreases as distances increase.
Figure 8.4: Elevation Angle Ionogram from Hawaii to
Colorado (5,300 km). Compare with Figure 8.1.
What does this all mean? It means
that a fixed radiation pattern will begin
supporting additional modes of propagation
(and thereby perhaps introduce additional
interference) as distance is increased. As
well, in order to eliminate multipathing
interference, transmitting antennas must
become more directional, with sharper
radiation patterns. Otherwise, signals will
begin to travel using more than one mode of
propagation and the receiver will (as a result)
experience an increase in multipathing signal
degradation.
Figure 8.4 shows that the MUF for the HF spectrum is associated with a 2-hop sig nal that
is transmitted between elevation angles of approximately 6.0 and 8.0 degrees. If the transmitting
antenna is incapable of concentrating energy below 8 degrees in elevation, then the 3-hop mode
of propagation must be used. Notice that the 3-hop mode of propagation has a sma ller MUF than
the 2-hop mode. Frequencies above the 3-hop mode MUF would therefore not be rece ived at all
if the transmitting antenna failed to radiate power below 8 degrees. You would t herefore be
restricted to communicating on frequencies less than 14 MHz. These are important concepts
which can be used to significantly improve communications between specific point s.
8.4 Applying the Results
The foregoing discussion used the results of a night-crossing signal path from H awaii to
Colorado during geomagnetically quiet conditions and a low sunspot number. In th is section, we
will apply the knowledge given in the last several sections toward understanding propagation
conditions that exist on a new path.
Let's consider the path from Texas (30N 100W) to the eastern U.S. (40N 75W) at 1 8:00
UTC (near local noon conditions) on 25 December 1991. The transmitter is in Texa s. This
corresponds to a geomagnetically quiet day (geomagnetic A-index of 7). The 12-mo nth mean
sunspot number for this date was 109. In addition, there were no flares or influ ential PCA
present during this analysis.
Our antenna has a primary radiation pattern that extends from 0 degrees in eleva tion angle
to about 50 degrees in elevation angle. We therefore used, as inputs to PROPLAB, a starting
elevation angle of 0 degrees, an ending elevation angle of 50 degrees, and we us ed an elevation
angle step rate of 0.5 degrees. In addition, we swept the HF spectrum using a st arting
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transmitting frequency of 1.0 MHz and an ending frequency of 40.0 MHz with a fre quency step
rate of 0.25 MHz (250 KHz). The small step rates used increased the accuracy of the results, but
required quite a few hours of computation time for the ray-tracing phase to fini sh. Nevertheless,
the results are quite impressive and very informative.
Figure 8.5 shows the results of the
propagation-delay plot for this path.
Immediately, several important parameters can
be determined: the number of supported
modes, the MUF of each mode, and the LUF
of each mode. There are four supported
modes of propagation: 1-hop, 2-hop, 3-hop,
and 4-hop modes. The MUF's of each of
these modes are: 34.25 MHz, 22.5 MHz,
17.25 MHz, and 14.75 MHz respectively.
Similarly, the LUF of the 2-hop mode is 5.25
MHz, the 3-hop mode is 6.5 MHz, and the 4hop mode is 8.0 MHz. The LUF for the 1hop mode (from this figure) is difficult to Figure 8.5: Propagation Delay Plot for the path from
determine since the traces for the 2-hop mode Texas (30N 100W) to the Eastern U.S. (40N 75W), a
distance of 2,520 km, on 25 Dec 1991 at 18:00 UTC.
intermix with the 1-hop mode and cannot be
discerned in these black and white renditions
of the display screens. Suffice it to say that the 1 and 2-hop modes have simila r LUFs in the
lower HF band near 5 MHz.
The signal path from Texas to the eastern U.S. is a daylit path. The electron de nsity
within the ionosphere is therefore at its highest level. Signals must therefore be of a higher
frequency in order to survive the strong D-region absorption which exists everyw here along this
path. This is the primary reason why the LUF is higher than in the previous exam ples.
Consider now Figure 8.6, which shows the results of the elevation angle plot for the path
from Texas to the eastern U.S.. This interesting plot differs from previous elev ation angle plots
presented, in that there are two sets of traces: one set for F-region reflection s, and another set
corresponding to E-region reflections. The small set of traces in the lower-left labelled "2-hop",
"3-hop", and "4-hop" are E-layer reflections. The highly ionized state of the E- region during the
day permits reflections from higher frequencies, provided the elevation angles a re low. This
figure then tells you that transmissions from Texas to the eastern U.S. can eith er be accomplished
through E-region reflections on lower frequencies, or F-region reflections on hi gh frequencies.
This information was not clearly evident in Figure 8.5.
Let's try to choose a frequency which should have decent signal quality, low-dis tortion,
and does not require very narrow antenna radiation patterns to achieve these res ults. The best
signal quality is obviously associated with the single-hop high-frequency signal s. If our antenna
radiates a fair amount of power between about 5 and 8 degrees in elevation angle , the 1-hop
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Figure 8.6: Elevation Angle Plot for the path from Texas
to the Eastern U.S. on 25 Dec 1991 at 18:00 UTC.
propagation mode on a frequency near the
FOT (0.85 x MUF) of 29 MHz should give
the best results. However, as these figures
illustrate, you have a fairly wide choice of
frequencies before additional modes begin
introducing significant levels of multipathing.
Frequencies between about 23 MHz and 34
MHz will give good communications. Note,
however, that if the MUF is approached too
closely, severe MUF-fading could begin to be
observed caused by the intermittent
penetration of the signals through the
ionosphere. A safer choice of frequencies
would be between 23 and 29 MHz.
Notice how the traces in Figure 8.6
curve back in on themselves near the MUF. The lower trace (prior to the sudden c urve at the
MUF) represents the low-angle rays. Low-angle rays are relatively stable and are the most
reliable rays to support communications. High-angle rays are much less stable, e xcept near localnoon where the electron density does not change significantly, and usually are m ore difficult to
sustain communications on. The high-angle rays are responsible for forming the u pper curves
in Figure 8.6 (curving from the lower-right to the upper-left) beginning at the MUF, or nose of
the traces. High angle rays can be discerned in almost all of the supported mode s of propagation
except perhaps the 4-hop mode and the E-region reflections. Under some circumsta nces, the
high-angle rays can support propagation on frequencies much higher than the basi c MUF.
If the transmitting antenna radiates most of its power between elevation angles of about
5 to 35 degrees, with a primary direction of radiation at about 15 degrees in el evation, then our
tactics must change. In this case, the usefulness of the 1-hop mode of propagati on will be limited
because most of the power radiated will not fall between the 5 and 8 degree elev ation angle
required to reach the receiver from Texas in one hop. However, some of the radiated power will
likely be received at the receiver. But the signal from the one-hop mode will al most certainly
be weak. For this reason, high-frequency communication above 23 MHz may be possi ble, but
difficult. Given that the transmitter radiates most of its power at about 15 deg rees in elevation,
it would probably be wiser to use a frequency between 17.5 MHz (just above the 3 -hop MUF)
and 22.5 MHz (the 2-hop MUF), and rely primarily on signals reflected twice by t he F-region
for communications. Selecting these bounds for frequencies will result in minima l multipathing
distortion. There will be some multipathing caused by weak 1-hop reflections, bu t most of the
signal strength should come from 2-hop signals since the primary radiation angle is closer to that
required for 2-hop propagation than for 1-hop propagation. Frequencies below abo ut 17.5 MHz
should probably be avoided, since they may be associated with more significant m ultipathing of
greater than 2 milliseconds (examine the difference in propagation times between 2-hop and 1hop propagation modes in Figure 8.5) caused by signals being received by both 1- hop, 2-hop, and
3-hop paths. Since our transmitter will not radiate much power above 35 degrees in elevation,
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4-hop signals should not be observed which will limit signal multipathing to the 3-modes of
propagation (1-hop, 2-hops, and 3-hops).
8.5 Commands Available While Viewing Ionogram Plots
There are several commands at your disposal while you view the ionogram plots pr oduced
by PROPLAB. These are summarized below:
Press "G" after the plot has been completed to save the screen image to the GIF- image
file "IONOGRAM.GIF". You can then use GIF-image viewing software to view the sav ed
image. The image will be saved according to the parameters established within PR OPLAB's
option menu (Main Menu option #8, suboption #17).
Press "P" after PROPLAB has finished plotting the ionogram to save the screen im age
in a PostScript compatible format for sending to a laser printer.
Press "H" after PROPLAB has plotted the ionogram to print the graphic screen to your
printer. You must first edit the text printer control file "PROPLAB.PTR" before this function
will work for your particular printer.
Pressing any other key will return you to PROPLAB's Main Menu. To re-examine (or
redraw) the ionograms using different parameters, choose Main Menu option #1, su boption #4
(Generate Oblique Sounder Ionogram), and at the prompt to "Analyze previously ge nerated
ionogram data?", select "Y". This will transfer control back to the ionogram ana lysis utility and
will let you reconstruct a new or different ionogram using different parameters.
SECTION 9 - COMPLEX AREA-COVERAGE MAPS
(Using the Complex Ray-Tracing Technique)
We use the term complex area-coverage maps to denote area-coverage maps that are
created from results of comprehensive (or complex) ray-tracing sessions - that i s, sessions which
use the complex ray-tracing technique. It does not allude to the complexity of t he maps.
Producing area-coverage maps using the results of complex ray-tracing sessions i s really quite
easy to do.
To display area-coverage (or broadcast coverage) maps when using the comprehensi ve
ray-tracing technique to trace rays, select Main Menu Option #6 and select the " C"omprehensive
method.
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The comprehensive broadcast coverage map generating utility is completely differ ent from
the software used to generate the simple broadcast coverage maps. This is primar ily because the
complex ray-tracing technique produces signal strength results as opposed to the signal quality
values that the simple technique produces.
Before a broadcast coverage map can be displayed, data must obviously be collect ed by
performing a ray-tracing session that uses the comprehensive ray-tracing techniq ue. This is
accomplished by first setting up the appropriate parameters in the Comprehensive Options Menu
(Main Menu Option #8, Suboption #18, with emphasis on Choice #21) and then initi ating the
comprehensive ray-tracing function through Main Menu Option #1.
For best results, the option supporting the ability to ray-trace signals by swee ping
elevation angles and frequencies and azimuths should be used, because this allows you to sweep
in two directions (in elevation and across in azimuth), which simulates realisti c transmissions.
However, if you are only interested in single azimuths, you can produce results by sweeping only
elevation angles (which keeps the azimuth constant). This has the advantage of s howing you the
effects of ionospheric tilts and non-great-circle propagation on specific azimut hs.
The remainder of this section makes the assumption that you have already complet ed a
ray-tracing session and are now within the utility to process the results into v iewable broadcast
coverage maps.
9.1 Types of Broadcast Coverage Maps Supported
The first menu presented by the comprehensive broadcast coverage mapping system
software lets you select the type of quantity you want to map. The first choice (which is the
default) lets you create a broadcast coverage map of the signal strengths of the rays that reached
the ground during the comprehensive ray-tracing session.
The second type of map that is supported is a map of propagation delays (in mill iseconds).
This choice creates a map that shows you how long it takes signals to travel fro m the transmitter
to the locations where the rays hit the ground. This may be used, for example, t o help in
determining multipathing that can affect digital communications.
The third type of map supported displays the maximum or minimum angles of arriva l
(elevation angles at the reception point where the ray reaches the ground). This is useful for
determining the range of angles (with respect to the horizon) that signals are r eceived. It can be
used to help in the selection of appropriate reception antennas (for example, an tennas that have
maximum gain within the range of indicated angles of arrival).
The fourth type of map shows you the geographical locations where the rays reach the
ground from the transmitter. It will display either ordinary or extraordinary ra ys (or both
together). This type of map is extremely useful for observing how far signals de viate from great-
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circle paths. It can also be used to display the skip-distance from the transmit ter more precisely
than the contoured signal quality maps provide and should be used to more precis ely determine
locations where skip distance focusing may be occurring.
The last choice of the menu does not produce a graphical map, but rather display s the
contents of the ray-tracing database file RAYOUT.DAT on-screen in a textual form at. This can
be very useful when you need to determine, for example, the precise signal stren gth (or other
characteristics) of the ray that most closely approaches the receiver location o r the characteristics
of signals that have a negative signal strength (non-existent, in other words).
9.2 Type of Rays to Include
PROPLAB's broadcast coverage mapping system will analyze ordinary or extraordina ry
rays (or both types of rays) to produce coverage maps. At this prompt, select th e type of rays
you want included in the analysis. The default is to include both types of rays, as both ordinary
and extraordinary rays are receivable by all antennas.
9.3 Specifying the Window Corner Coordinates of the Map
When PROPLAB produces a broadcast coverage map using the results of a comprehens ive
ray-tracing session, it builds a geographical map that includes all of the area covered by the
great-circle path between the transmitter and receiver. It does this by computin g a "viewing
window" through which the results of the ray-tracings are presented.
PROPLAB asks you to type in the geographical latitude and longitude of the left corner
of this window (either the left-top or left-bottom corner). It then asks you to type in the
coordinates of the right-corner of the window (either right-top or right-bottom) . The rectangular
window formed from these two corners forms the basis for the viewing window. Any
geographical details contained within the window are displayed.
Positive coordinates refer to northern latitudes and western longitudes. Negativ e values
refer to southern latitudes and eastern longitudes.
9.4 Specifying Limits for Collected Data
PROPLAB will let you define specific limits to the data in the ray-tracing database. If
a specific ray within the database falls within the acceptable limits you establ ish, the ray will be
accepted and processed. If the ray falls outside of the specified limits, PROPLA B will ignore
the ray and will not include it in the analysis.
The items which can be selected as limiting factors are known as filters. PROPLAB
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contains five filters which can be applied to the ray-tracing database. They are described below.
The "Elevation Angle" filter lets you specify the upper and lower limits for elevation
angles of arrival . For example, to include rays which have angles of arrival between 7 and 30
degrees, you would specify an upper limit of 30 degrees and a lower limit of 7. Rays less than
7 degrees or more than 30 degrees will be excluded from the analysis.
Similar filters exist for rays with differing azimuths, frequencies, signal stre ngths and
ground ranges. By specifying upper or lower limits on any of these filters, you can very
selectively target sections of the ray-traced database for inclusion in the anal ysis.
9.5 Other Map and Contouring Options
The remaining prompts presented by PROPLAB are identical to those prompts given when
constructing Global Ionospheric Maps. Consult that section of this manual for mo re information
regarding these prompts.
A few side-notes are required with regards to the selection of the minimum conto ur to use.
When generating signal strength maps or maps of minimum elevation angles (and po ssible other
types of contoured maps), PROPLAB usually uses a minimum contour value of zero. This lets
you determine where along the signal path signal strengths are zero or greater, etc. If the default
of zero is used, PROPLAB may (while drawing the contours) plot small regions out side of the
main zero contour that also contain zero contour levels. In other words, there m ay be satellite
or island regions of contours labelled as zero. These small isolated island regi ons are a result
of the pre and post-processing that occurs on the data to make it fit into the a llocated map
properly. They can (and should) be ignored. Alternatively, you can filter out th ese island regions
by specifying a minimum contour value that is close to zero but is slightly posi tive (ex. 0.1 or
0.2). This will help clean up the display if you find it too messy.
9.6 Database Offset Value
The broadcast mapping software is only able to handle up to 2,000 datapoints at a time.
That is, if you have traced more than 2,000 rays during a previous ray-tracing s ession, only the
first 2,000 points will be used. By specifying filter limits, you can increase t his number almost
indefinitely by ignoring rays with certain undesirable characteristics. However, there is another
way around this limitation.
The last question prompted by the mapping software asks you to specify an offset into the
database. Normally, the offset is set at zero which means that PROPLAB will begi n processing
data at the very beginning of the database. By increasing this offset value, you instruct
PROPLAB to begin skipping records in the database. If you have, for example, 300 0 rays in the
117
database (each ray occupies one record), then specifying an offset value of 1000 would force
PROPLAB to skip the first 1,000 records in the database. It would therefore begi n accepting data
for analysis beginning with the 1,000th ray record.
Use this offset to analyze sections of your database that might not have been an alyzed
previously due to the size of your database.
9.7 The Plotted Map
After all of the prompts have been answered, PROPLAB begins reading in the datab ase
and filtering out those values which do not fit within the specified limits. The default limits
should be more than sufficient to accept all of the data in the database. That is, if you do not
specify or change any of the limits, PROPLAB will use the entire database.
After the data has been read, it is processed and the appropriate contouring mat rices are
established.
Following this (which will take some time depending on the resolution level you have
selected and the speed of your computer), PROPLAB will clear your screen and beg in plotting
any geographical features that exist within the viewing window. This phase may a lso require a
little bit of time since PROPLAB references the high-resolution geographical dat abase of more
than 100,000 coordinate pairs to create the geographical map. You can force PROP LAB to stop
plotting the geographical features by pressing the ESCape key once during this p hase.
PROPLAB now traces the great-circle path from the transmitter to the receiver. T his is
a useful reference line that can help determine whether or not signals are follo wing or deviating
from the anticipated great-circle path (and by how much).
The next step PROPLAB takes is to begin the contouring phase (if the map require s
contouring). For maps which only plot the geographical locations where rays hit the ground, this
step is skipped. All other maps begin the contouring. You can interrupt the cont ouring at any
time by pressing the ESCape key once.
The map is considered complete after the map is titled at the bottom edge of the screen.
When this occurs, you have several additional commands at your disposal. You can generate GIF
or PostScript images of the screen by pressing the "G" or "P" keys respectively. You can send
the screen to your dot-matrix printer by pressing the "H" key. Or you can return to the
PROPLAB Main Menu by pressing any other key such as the ESCape key.
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SECTION 10 - ANTENNAS
PROPLAB PRO Version 2.0 comes equipped with numerous types of antennas that can
be immediately selected and put to work. Main Menu Option #10 places you in the antenna
selection menu.
PROPLAB will also process custom-made antenna files that contain custom-built an tenna
radiation patterns. PROPLAB will not compute the radiation pattern based on the orientation of
your antennas radiation elements. To do this, you must use other types of softwa re.
10.1 Selecting Existing Antennas
From the antenna menu, scroll through the list by pressing ENTER until you find an
antenna that most closely approximates your own. Then enter the number beside th at antenna
to select it.
The information presented beside each selectable antenna in the antenna menu giv es
important information about each antenna. The maximum gain figure describes the maximum
gain of the antenna, relative to an isotropic radiator. An isotropic radiator is an antenna that
radiates equal amounts of power in all directions. It therefore has zero gain be cause it spreads
all of its power equally in all directions. Antennas that have measurable gain v alues create that
gain by concentrating energy flux into specific directions. This requires energy to be sacrificed
in other radiated directions. So antennas with large gains are usually highly di rectional.
Antennas with low gains are more omnidirectional. The maximum gain value listed is given in
units of decibels (or dB) above those of an isotropic antenna.
The azimuth of maximum gain describes the direction of the main radiation lobe of the
antenna. For example, an antenna that has a maximum gain at an azimuth of 0 (zer o) degrees
means that the main lobe of the antenna points due north. This information is us ed by
PROPLAB to determine gain figures at other azimuth angles during ray-tracings.
10.2 Displaying the Radiation Pattern
After the antenna has been selected, PROPLAB asks you if you want to display the
radiation pattern of the selected antenna. If you answer "Y"es to this prompt, P ROPLAB clears
the screen and draws two graphical images on-screen. The image on the left descr ibes the
radiation pattern of the antenna as the transmission elevation angle (or takeoff angle) is increased
from 0 degrees to 90 degrees. The image on the right describes the radiation pat tern of the
antenna in terms of the azimuthal angle from 0 degrees (true north) to 360 degre es (where 90
degrees points due east, etc).
119
You can save this graphical screen containing the antenna radiation pattern to a GIF or
PostScript file by pressing the "G" or "P" keys respectively. You can print out the radiation
pattern to your printer by pressing the "H" key. Any other key returns you to th e Main Menu
of PROPLAB.
All future ray-tracing operations (whether performed using the simple or compreh ensive
techniques) will reference the newly selected antenna.
10.3 Creating Your Own Antenna Radiation Patterns or Modifying/Deleting Existing
Patterns
All of the antenna radiation patterns used by PROPLAB are stored in the subdirec tory
"ANTENNAS". Using a text editor, you can view or modify the contents of any of t hese
radiation patterns.
To delete an existing radiation pattern so that PROPLAB can no longer use it, si mply
delete the required antenna radiation pattern file from the ANTENNAS subdirector y.
To create your own radiation pattern, copy the template file "BLANK.DAT" to another
file of your choosing (remembering to keep the name of your new file uniquely di fferent from
the existing files so you don't accidentally overwrite an existing antenna radia tion pattern). For
example, to create a radiation pattern describing the characteristics of a short wire antenna , we
could copy the antenna template file BLANK.DAT to a new file named "SHRTWIRE.DAT ".
Notice that the antenna radiation patterns must all have the extension .DAT. Fai ling to observe
this requirement will make PROPLAB blind to the antenna file.
After we have copied the template file to our newly named antenna radiation patt ern file,
we can use a standard text editor to modify our new antenna file. Within each of the antenna
files are specific key words (or acronyms) that are used by PROPLAB to define re quired
parameters. Lines that are prepended with an asterisk are treated as comments an d are ignored.
The following acronyms are defined:
DESCRIPTION = Place your description of the antenna on this line, limited to 80 characters
(which includes the word "DESCRIPTION:" which appears on the same line).
MAXANTENNAGAIN = The value placed directly to the right of this acronym defines the
maximum gain of the antenna in the direction of MAXGAINAZIMUTH described below. The
maximum gain given here must be given in units of decibels relative to an isotro pic radiator.
MAXGAINAZIMUTH = The maximum gain of the antenna occurs in this direction, which is
measured in degrees clockwise from true north. True north is therefore zero degr ees. East is 90
degrees, west is 270 degrees, etc.
120
VGAIN = This acronym is used to mark the beginning of the values that describe the radi ation
pattern of the antenna in the vertical plane (that is, in elevation or takeoff a ngles). There must
be 90 numerical values that follow the VGAIN acronym and each value must be on the right-side
of an equal sign. The left-side of the equal sign must contain the elevation angle for which the
gain value applies.
In actuality, the values following the VGAIN acronym are loss values that are relative to the
maximum gain of the antenna (defined using MAXANTENNAGAIN ). For example, if the
maximum gain of an antenna is 24 dB and the VGAIN value entered at an elevation angle of 10
degrees is 20 dB, then the actual gain of the antenna at that angle of elevation would be only 4
dB (24 dB minus 20 dB). A value of zero dB would correspond to an antenna gain o f 24 dB.
A value of 30 dB would correspond to an antenna gain of -6 dB (or a loss of 6 dB). Be careful
when entering radiation pattern values here. All values must be relative to the maximum gain
of the antenna. It is therefore impossible to have VGAIN values that are negative, for this would
imply that the antenna had gains that exceeded the maximum specified gain of the antenna, and
this is not possible.
HGAIN = This acronym is used to mark the beginning of the values that describe the radi ation
pattern of the antenna in the azimuthal plane. There must be 360 numerical value s that follow
the HGAIN acronym. On each of these lines, there must be two values separated by an equal
sign with the HGAIN value describing the signal strength gain (in dB relative to the maximum
gain of the antenna) on the right-side of the equal sign and the azimuth on the left-side .
Exactly the same procedure applies to these values as applied to the VGAIN values. Again, all
values must be relative to the maximum gain of the transmitter as stated beside the acronym
MAXANTENNAGAIN . Negative values are therefore impossible for the same reason as above.
After you have modified the antenna file, save it to disk and run PROPLAB. Then select
the antenna from the antenna menu (Main Menu Option #10) and view the radiation pattern to
make sure it is correct. If you can't find your antenna in the antenna menu, you probably saved
your antenna file to the wrong directory. Make sure all antenna files are saved in the
"ANTENNAS" subdirectory. PROPLAB will not search elsewhere for them. Also, make certain
your antenna file has the extension ".DAT" (ex. SHRTWIRE.DAT). PROPLAB will igno re files
that do not have this extension.
SECTION 11 - REAL-TIME MAPS
PROPLAB PRO Version 2.0 comes equipped with an exceptionally powerful new functi on
that will produce real-time maps on your computer. You can even display the current local times
for any number of cities around the world, all updated at user-specified interva ls.
121
This function gives amateurs radio operators, for example, the ability to speak with friends
on the radio while at the same time looking at real-time maps of ionospheric con ditions, grayline
locations and local times for cities around the world (including your friends lo cal time). This is
a significantly useful tool.
For this function to operate properly, a Plate Carree map must exist in your map library.
If one does not exist, create one using the MAKEMAP utility. If you have more th an one Plate
Carree map in your map library file, you can select any of them to use here.
11.1 Setting the Gray Angle
The Gray Angle differs from the grayline in the following way. The grayline defines the
regions of the world where the Sun is exactly zero degrees in elevation (that is , it is exactly on
the horizon and is either rising or setting). The gray angle, on the other hand, defines the regions
of the world where the Sun is a user-specified number of degrees in elevation above or below
the horizon.
For example, to identify the regions of the world where the Sun is 20 degrees be low the
horizon (which, by the way identifies the ending of astronomical twilight), you would enter a
gray angle of -20 degrees. Positive values correspond to elevation angles of the Sun that are
above the horizon. Negative values refer to locations where the Sun is below the horizon.
PROPLAB will plot the gray angles corresponding to elevation angles between -60
degrees and + 60 degrees. A gray angle value of zero degrees coincides with the grayline.
11.2 Real-Time Global Ionospheric Maps
Perhaps the most powerful feature of PROPLAB's real-time mapping system is its a bility
to produce real-time global maps of ionospheric characteristics. PROPLAB will pr oduce realtime maps of any of the mappable ionospheric characteristics described in the Se ction titled
"Global Ionospheric Maps." In fact, many of the prompts which must be answered i n that section
are also required to produce real-time maps. Refer to the "Global Ionospheric Ma p" section for
information on how to respond to the various prompts.
PROPLAB will produce real-time maps of ionospheric critical F2 layer frequencies ,
maximum usable frequencies for 3000 km (or variable-distance) paths, critical E- layer
frequencies, M-factors for 3000 km distances, maximum heights of electron densit ies, solar zenith
angles (which are 90 degrees minus the elevation angle of the Sun above the hori zon - essentially
solar elevation angles), and various maps of the Earth's magnetic field. PROPLAB will also
produce real-time transverse plasma frequency maps of the ionosphere between any two points
on the Earth. This latter map shows you a picture of the ionospheric layers and lets you see how
the structure of the ionosphere changes in real-time. The magnetic field maps ar e not updated
122
in real-time because their parameters change too slowly to observe (even over ti me-scales of
years). For example, magnetic latitudes are related to the location of the geoma gnetic poles and
the poles only change minutely from year to year. Hence, mapping the geomagnetic field
parameters in real-time is not really practical. All of the other maps, however, are updated in
real-time.
11.3 Update Rates for the Real-Time Maps
The real-time maps displayed by PROPLAB can be updated at user-defined intervals of
minutes. For example, the grayline can be updated once every minute if desired b y specifying
an update rate of 1 minute. Specifying an update rate of 0 (zero) minutes forces PROPLAB to
continually update the display as quickly as possible.
For contoured maps such as maps of maximum usable frequencies, the timer starts ticking
as soon as the map is finished being drawn. If your system requires several minu tes to draw a
contoured global map of maximum usable frequencies and you specify an update rat e of 1 minute
for these maps, PROPLAB will pause for one minute after it has finished drawing the map before
it begins working on the computations to draw the next map after the 1 minute in terval has
expired.
11.4 Displaying Local Times for Cities Around the World
The local times for cities around the world can be displayed if a file by the na me of
"CITYTIME.DAT" exists in the same directory as the PROPLAB software. This file s hould
describe cities (geographical locations and time-zone information) in the same f ormat as the
geographical location database file "PROPLAB.LOC". PROPLAB already comes loaded with
a few cities in the CITYTIME.DAT file whose local times can be displayed in real -time as soon
as you load up PROPLAB.
Since the CITYTIME.DAT file is in exactly the same format as the main geographic al
database file PROPLAB.LOC, if you want to include other cities in the CITYTIME.D AT file so
that they are also displayed on-screen when you do real-time mapping, simply use your text
editor to copy the lines containing the desired cities from the PROPLAB.LOC file to the
CITYTIME.DAT file. Since these are both text files, modifying them or adding cit ies to them
is as simple as loading your text editor and changing them.
To display all of the local times associated with the locations listed in the geographical
database, use the DOS "copy" command to copy the PROPLAB.LOC file to the CITYTIM E.DAT
file. For example, type "copy PROPLAB.LOC CITYTIME.DAT". This will place a copy of the
geographical database in the CITYTIME.DAT file. Now, every time you produce real -time maps,
all of the local times for each of the locations defined in the PROPLAB.LOC file will be
displayed on-screen and updated at the intervals you specify.
123
A prompt presented by PROPLAB in the real-time mapping function asks you if you want
to display the names of cities on-screen as well as their local times. If you specify "Y"es here,
PROPLAB will display the names of the cities above the dot which identifies the location for the
city. The local time for that city is then displayed below the identifying dot. If you have a large
number of cities to display, you might not want to include the names, because fo r large numbers
of cities, the screen can quickly become saturated with city names that overlap one another. For
a smaller number of cities, this can be useful to help you keep track of the cit y names.
11.5 Commands Available While Viewing Maps
There are several useful commands that are at your disposal while viewing maps i n realtime. The standard screen-saving functions "G", "P", and "H" keys can be pressed to save
screens to GIF format, PostScript format and to your local dot-matrix printer (r espectively).
You can also use your mouse to set new transmitter and/or receiver locations. Th e
method used to accomplish this is identical to the method of setting up the tran smitter and
receiver locations described earlier in this manual. Press and release the left mouse button to
define the transmitter location. Then move the mouse pointer to the location of the receiver and
press (and release) the right mouse button. The great-circle path, distance and bearing are then
instantly displayed on-screen with X's marking the new locations for the transmi tter and receiver.
You can keep the transmitter fixed in location and change the receiver location by moving the
mouse and pressing (and releasing) the right mouse button at each new desired re ceiver location.
This is desirable if you have several reception points you want to examine from one transmitter.
PLEASE NOTE that PROPLAB does not change the actual location of the transmitter
and receiver that is used by the rest of PROPLAB's modules. Changing the transmitter and/or
receiver locations in this real-time mapping system module lasts only as long asyou are in the
real-time mapping system program. As soon as you return to PROPLAB's Main Menu or
( to
DOS), the original transmitter and receiver locations are restored.
Two remaining commands that can be used while viewing the maps are the "+" (plus ) and
"-" (minus) keys. The plus key causes PROPLAB to increase the geomagnetic A-inde x by one
point. The minus key causes PROPLAB to decrease the geomagnetic A-index by one c ount.
This feature lets you adjust the ionospheric maps that may be dependent on geoma gnetic activity
(which applies to most of the maps except the geomagnetic ones). It is therefore possible to be
running PROPLAB in the real-time mode and continuously adjusting the A-index eve ry three
hours when new geomagnetic activity values are broadcast by radio stations WWV o r WWVH
at 18 minutes past each hour on 2.5, 5, 10, 15, and 20 MHz. Incrementing the A-i ndex values
will also affect the location of the auroral zones, which will migrate southward and expand in
size with larger geomagnetic A-indices.
With these commands at your disposal, it should be easy to see how useful the sy stem
could be for those who regularly communicate with others around the world (as am ateur radio
124
operators do). The ability to explore different paths, determine which ones cros s into the auroral
zones and by how much, as well as the changing ionospheric characteristics that occur along each
path and the ability to see these changes in real-time, is an invaluable additio n to PROPLAB!
SECTION 12 - HOURLY MUF GRAPHS
Most radio propagation programs are capable of displaying the maximum usable fre quency
(MUF) as a function of time. PROPLAB is no longer an exception. PROPLAB PRO Vers ion
2.0 will now compute and graph the maximum usable frequency between a given tran smitter and
receiver over a period of 24 hours. It will also graph several other important l ines at the same
time which will help guide the user into selecting appropriate transmission or r eception
frequencies.
The hourly MUF graphs are produced by using the simple ray-tracing technique to search
for and locate MUFs and E-layer maximum usable frequencies. The E-layer MUFs are critical
for determining the lowest frequency which will penetrate the E-layer. This is important for longdistance communications because long-distance communications can only be accompl ished if the
signals are reflected from the F-layers (which reside above the E-layer). Signal s must therefore
be high enough in frequency to punch through the E-layer but must also be low en ough in
frequency to be reflected by the F-layers and not penetrate them. These graphs a re ideal for these
purposes and give you a good idea when specific bands may open or close through the course
of a day.
There are no required prompts to produce an MUF graph. The only parameters requi red
are set within the Options menu (Main Menu Option #8). The transmitter and recei ver locations,
time of day and sunspot number or solar flux value are all that is required.
PROPLAB produces the MUF graphs by first collecting the MUF data for the given p ath
for every hour of the day. Twenty-four MUF values are therefore collected. Durin g this phase,
PROPLAB shows you the UTC hour for which the MUF is being computed. It also disp lays the
progress of the computations by plotting a period ("."), a vertical bar "|" and the letter "e". The
period simply indicates that PROPLAB is busy working on the problem. For paths t hat are
greater than 4,000 kilometers (and therefore require more than one hop), PROPLAB computes
two MUF values at two separate control points spaced approximately 2,000 kilometers from each
end of the path. These control points correspond to the path midpoints for one-h op distances
4,000 kilometers from each end of the path. When the first MUF is computed and t he second
MUF is about to begin being computed, PROPLAB prints the vertical bar. The "e" i ndicates that
PROPLAB is busy computing the E-layer MUF for the control point in question.
125
The Figure to the left shows an
example of an MUF graph. The MUF of the
F2 layer is the top-most line. The next line
down is the Optimum Working Frequency (or
FOT) and is 85% of the MUF. The thin line
below the FOT is the numerical average of
the MUF and the bottom line, which is the EMUF (also known as the E-layer cutoff
frequency).
For short-distance transmissions,
frequencies should be kept below the E-layer
MUF. If frequencies exceed the E-layer
MUF, the signals will penetrate the layer and
travel to the F-layer for reflection, which results in long-distance communicati ons. This is
desirable if you are only interested in long-distance communications where F-lay er signal
propagation is a must. In this case, the chosen frequency must reside between th e E-layer MUF
and the F-layer MUF. If the frequency you choose is above the F-layer MUF, the s ignals will
penetrate the ionosphere and be lost to space.
The optimum working frequency (the FOT line) in the above graph is a line which tends
to result in the most reliable communications (statistically speaking). However, there are often
a range of frequencies near the FOT that can be used reliably. This range of fre quencies is
indicated by the thin line in the Figure above. This line is the average of the F-layer MUF and
the E-layer MUF. The range of most useful frequencies is indicated by the spacin g between the
FOT line and this thin line. In the above example the FOT line tends to represen t the upper-limit
for useful frequencies while the thin line below it represents an estimated low- limit for useful
frequencies. From about 11:00 UTC to 13:00 UTC, the distance (or range of freque ncies)
between the FOT line and the thin line decreases until they finally cross one an other. This
indicates a narrowing of the range of most useful frequencies. Between about 13: 00 UTC and
21:00 UTC the FOT line represents the lower limit of optimum frequencies while t he thin line
represents the upper-limit. After they cross again shortly after 21:00 UTC, the thin line becomes
the lower-limit and the FOT line becomes the upper-limit. In these ways, users c an determine
the most reliable range of frequencies at a given time during the day.
In addition to the sunspot number (or solar flux), time of day and the coordinat es of the
transmitter and receiver, PROPLAB also includes effects of enhanced geomagnetic activity
through the geomagnetic A-index figure. A sample map given for the same path as the one
above is presented below. The difference is the geomagnetic A-index is 100 (seve re storm
conditions). Notice the dramatic reduction in the MUF and how this effectively narrows the
range of usable frequencies.
The time between approximately 13:00 UTC and 15:00 UTC shows a region where the
126
F2-layer MUF is below the E-layer MUF.
This is significant because it shows that
signals that penetrate the E-layer will also
penetrate the F2-layer and be lost into space.
Therefore, during that time interval F2-layer
propagation is not possible and you would be
limited only to E-layer propagation over
shorter distances.
For most other times of the day,
communications is possible via the F-layer
only through narrow bands of frequencies.
The width of the usable frequencies increases
substantially during the night-time (from
02:00 to about 12:00 UTC). However, levels of noise and absorption will definite ly be higher
because of the depressed MUF values for that time period. Communications on the higher bands
is not possible except during daylight.
While viewing the graphical results, you can press "G" or "P" to save the result s to GIF
or PostScript files respectively. You can also print the results on your dot mat rix printer by
pressing the "H" key. Press any other key to return to PROPLAB's Main Menu.
127
INDEX
A-index 8, 100
Absorption 111
Altitude grid
adjusting the height 50
Angles of elevation 109
Antenna template 119
Antennas 90, 118
acronyms 119
creating 119
directional 54
omni-directional 54
Apogee 56
Aurora australis 9
Aurora borealis 9
Aurora Zone
aurora borealis 9
Auroral absorption 11
Auroral activity 9
Auroral Oval Simulator 25
Auroral sporadic-E 11
Auroral zone 9
aurora australis 9
auroral absorption 11
Auroral activity (processes)
9
auroral sporadic-E 11
electrons 10
northern lights 9
oval 9
radio propagation 10
signal degradation 10
significance 10
sporadic-E 11
Auto-SSN-Calculation 38
AutoQTH 29
Basic MUF 112
Books
ionospheric 1
propagation 1
Bugs 27
C-layer 2
CCIR 19
Central meridian 6
Chromosphere 4, 5
CME 5
Collision frequency
shaping parameters 50
Contours 98
flashing screen box 75
Corona 4
Coronal mass ejections 5
Cosmic Ray layer 2
Critical frequencies 75
foE 18
foF1 18
foF2 18
Critical frequency 68
critical frequency 17
Cutoff latitude 12
D-region
location 2
Data gaps 52
Defining sporadic-E
with a mouse 68
without a mouse 69
Defocusing 23
Directional antennas 54
Disappearing filaments 5
DSF 5
Ducting 63
DX 3
E-region 2
Effective sunspot number 24
Electron densities 58
Electron density 3, 86, 111, 112
peak 2
Electron density profiles 56
Elevation angle plot 111
Elevation angles 103
Environment 3
Equatorial anomaly 76
Es
location 2
EUV 2
128
Evanescent 45
Extreme ultraviolet light 2
F-region 2
F1 2
F2 2
F1 2
F2 2
Filters 115
Flare locations 6
Flares
PCA 12
proton flares 12
FoE 79
foF2
minimum 19
FOT 112, 125
Gamma 8
Generating maps 25
Geographical locations
Defining 29
grid-coordinate 29
name entry 29
numerical entry 29
Geomagnetic 100
A-index 8
disturbance 8
gamma 8
K-index 8
nanotesla 8
nT 8
storm 3
substorm 3
sudden storm commencement
6
Geomagnetic storms 78
GIF 41, 75
GIF-image 113
GLE 12
Gradients 76
Gray angle 121
Grayline 30, 121
Grayline signal 76
Graylines 1
Great-circle 20
Great-circle paths 1
Grid bounds 59
Grid distance 47
Ground Level Event 12
Group path 65
Gyrofrequency 50
Heights
hmD 18
hmE 18
hmF1 18
hmF2 18
Helium 4
High-angle rays 23, 112
HmF2 79
Hourly MUF 124
Hydrogen 4
Hydrogen-Alpha 5
Imaginary 87
Install 25
Integration
Adams-Moulton 44
Runge-Kutta 44
Interaction 3
International Reference Ionosphere
19
Interpolation 61
Ionogram
elevation angles 108
optimum angles 108
propagation-delay 104, 111
Ionogram database 100
Ionograms 99
Ionosonde 99
critical frequency 17
frequency sweep 17
penetration frequency 17
sweep-frequency 99
Ionosondes 17
Ionosphere 2
location 2
structure 2
Ionospheric focusing 22
Ionospheric models 32
IRI 19
129
K-index 8
Lateral distance grid 47
Long Paths 32
Low-angle rays 112
Lowest Useful Frequency 111
LUF 111
M-factor 72
M-factors 77
Magnetic disturbance 8
Magnetic field
models 42
Magnetosphere 3
appearance 3
Map library 25
Map projections 97
Maximum gain 118
Maximum height 79
Maximum usable frequencies 22
Maximum Usable Frequency 1, 3,
105
Median 37
Models
CCIR 19
URSI 19
Modes 111
Modes of propagation 105
MUF 1, 3, 98, 105, 108, 125
MUF fading 94
MUF graph 125
MUF(3000) 72
MUF-fading 112
Multipath ranging 95
Multipathing 105, 107, 109, 112
Nanotesla 8
Northern lights 9
Oblique Ionogram 99, 102
Oblique ionograms 99
Oblique sounding ionograms 98
Omni-directional 54, 90
Options Menu 28
PCA 12, 100
Penetration frequency 17
Perigee 56
Photosphere 4
Photospheric temperature 3
Plasma frequency 18
Polar Cap Absorption 12
cutoff latitude 12
diurnal pattern 13
GLE 12
riometer 12
Polarization 65
PostScript 41, 113
Propagation
after sunset 19
before sunrise 19
Propagation delay 95
Propagation delays 103
Proton flares 12
Radiation
EUV 2
extreme ultraviolet light 2
lyman alpha 2
soft x-rays 2
Radiation pattern 110
Radio Blackout
cross identification 87
Radio waves
history 1
Ray 14
Ray Tracing Screen
impounding the signal 87
Ray-tracing model 41
Ray-tracing techniques 23
comprehensive (or complex)
24
simple 24
Real-time mapping system 30
Receiver height 45
Reflect 1
Reflection 14
Refraction 2, 14
definition 1
history 1
maximum 2
Rotating Grids 48
Satellite anomalies
charging 6
130
tumbling 6
Save screen images 41
Scientific notation 86
Short Paths 32
Short wave fadeouts 80
SI 5
Signal quality 104
Skip distance 22
Skip distance focusing 115
Skip distances 22
Skip fading 94
Skip tracing rays 89
Solar elevation angles 79
Solar flares 5, 100
locations 6
Solar flux 100
Solar radio flux 37
Solar wind 3
Solar zenith angle 73
Solar zenith angles 79, 80
Spectrum Analysis 98
Oblique Ionogram 99
Sporadic-E 2, 11, 68, 90, 100, 105
SSC 6
Sudden impulse 5
Sudden storm commencement 6
Sun 3
average radius 3
central meridian 6
chromosphere 4
corona 4
coronal mass ejections 5
differential rotation 4
distance 3
gravitational pull 3
interior 4
magnetic fields 4
mass 3
photosphere 4
rotation rate 3
Sunspots 4
temperature 4
volume 3
Sunrise 19, 30
Sunset 19, 30
Sunspot 37
Sunspot number 100
Sunspots 4
bipolar 5
direction of rotation 4
magnetic fields 4
temperature 4
Superimpose 98
Sweep 17
Sweep-frequency 99
SWFs 80
Terminator 1
Terrestrial 3
Three-dimensional ionosphere 58
Time zone 29
Transmitter height 45
Transmitter power 36
Transverse plasma frequency map
81
Twilight 30
Universal time 29
URSI
URSI 19
Usable bandwidth 3
UTC 29
Viewing window 46
Warnings
grid bounds 59
World Warning Agency 68
WWA 68
X-rays
soft 2
Zoom 49
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