Construction-and-Propagation-of-Radio

Construction-and-Propagation-of-Radio
MCI 2515H
MARINE CORPS INSTITUTE
ANTENNA CONSTRUCTION
AND PROPAGATION OF
RADIO WAVES
MARINE BARRACKS
WASHINGTON, DC
UNITED STATES MARINE CORPS
MARINE CORPS INSTITUTE
912 POOR STREET S. E.
WASHINGTON NAVY YARD DC 20391-5680
IN REPLY REFER TO:
1550
Ser 2515
10 July 01
From: Director
To:
Marine Corps Institute Student
Subj: ANTENNA CONSTRUCTION AND PROPAGATION OF RADIO WAVES
(MCI 2515H)
1. Purpose. The MCI 2515H, Antenna Construction and Propagation of Radio Waves, provides
communicators with instructions in selecting and/or constructing the appropriate antenna(s) for
use within the current field.
2. Scope. This course is designed as a course of study on the propagation of radio waves and the
construction and repair of conventional and field expedient antennas.
3. Applicability. This course is intended for instructional purposes only. This course is
designed for Marines in the ranks of private through gunnery sergeant in occupational fields
2500 and 2800.
4. Recommendations. Comments and recommendations on the contents of the course are
invited and will aid in subsequent course revisions. Please complete the course evaluation
questionnaire at the end of the final examination. Return the questionnaire and the examination
booklet to your proctor.
G. E. GEARHARD
Deputy
(This page intentionally left blank.)
Table of Contents
Page
Contents........................................................................................................................
i
Student Information ......................................................................................................
iii
Study Guide..................................................................................................................
v
Study Unit 1
Radio Communications ..............................................................
1-1
Radio Sets and Waves ................................................................
Carrier Waves and Modulation...................................................
1-3
1-13
Propagation of Radio Waves ......................................................
2-1
The Atmosphere.........................................................................
Ground Waves and Sky Waves...................................................
Maximum Usable Frequency (MUF) and Lowest Usable
Frequencies (LUF) ....................................................................
Fading ........................................................................................
The Effects of Frequency on Wave Propagation .........................
2-3
2-15
Antennas ....................................................................................
3-1
Functions of an Antenna and Antenna Radiation ........................
Antenna Polarization ..................................................................
Conventional Antennas ..............................................................
Field Expedient Antennas...........................................................
Transmission Lines ....................................................................
3-3
3-11
3-21
3-33
3-47
Site Selection and Antenna Grounding .......................................
4-1
Requirements for Site Selection..................................................
Electronic Warfare Considerations .............................................
Grounds and Counterpoises........................................................
4-3
4-11
4-17
Appendix A
Field Expedient Antenna Construction .......................................
A-1
Appendix B
Joint Spectrum Center (JSC) ......................................................
B-1
Review Lesson..............................................................................................................
R-1
Lesson 1
Lesson 2
Study Unit 2
Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5
Study Unit 3
Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5
Study Unit 4
Lesson 1
Lesson 2
Lesson 3
MCI Course 2515H
i
2-23
2-29
2-37
(This page intentionally left blank.)
MCI Course 2515H
ii
Student Information
Number and
Title
MCI 25.15h
ANTENNA CONSTRUCTION AND PROPAGATION OF RADIO WAVES
Study Hours
11
Course
Materials
Text
Review Agency
Marine Corps Communications-Electronic School, Marine Corps Air Ground
Combat Center, Twentynine Palms, CA 92278
Reserve
Retirement
Credits (RRC)
4
ACE
Not applicable to civilian training/education
Assistance
For administrative assistance, have your training officer or NCO log on to the
MCI home page at www.mci.usmc.mil to access the Unit Verification Report
(UVR) or MCI Hotline. Marines CONUS may call toll free 1-800-MCIUSMC. Marines worldwide may call commercial (202) 685-7596 or
DSN 325-7596.
For assistance concerning course content matters, call the Distance Learning
Technologies Department’s Support Division at DSN 325-7516 or
commercial (202) 685-7516, or log on to the MCI home page at
www.mci.usmc.mil/feedback/course developers.
MCI Course 2515H
iii
(This page intentionally left blank.)
MCI Course 2515H
iv
Study Guide
Congratulations
Congratulations on your enrollment in a distance training course from the
Distance Learning Technology Department (DLTD) of the Marine Corps
Institute (MCI). Since 1920, the Marine Corps Institute has been helping tens
of thousands of hard-charging Marines, like you, improve their technical job
performance skills through distance training. By enrolling in this course, you
have shown a desire to improve the skills you have and master new skills to
enhance your job performance. The distance training course you have
chosen, MCI 2515H, Antenna Construction and Propagation of Radio Waves,
provides communicators with instructions in selecting and/or constructing the
appropriate antenna(s) for use within the current field.
Your Personal
Characteristics
•
YOU ARE PROPERLY MOTIVATED. You have made a positive
decision to get training on your own. Self-motivation is perhaps the most
important force in learning or achieving anything. Doing whatever is
necessary to learn is motivation. You have it!
•
YOU SEEK TO IMPROVE YOURSELF. You are enrolled to improve
those skills you already possess, and to learn new skills. When you
improve yourself, you improve the Corps!
•
YOU HAVE THE INITIATIVE TO ACT. By acting on your own, you
have shown you are a self-starter, willing to reach out for opportunities to
learn and grow.
•
YOU ACCEPT CHALLENGES. You have self-confidence and believe
in your ability to acquire knowledge and skills. You have the selfconfidence to set goals and the ability to achieve them, enabling you to
meet every challenge.
•
YOU ARE ABLE TO SET AND ACCOMPLISH PRACTICAL
GOALS. You are willing to commit time, effort, and the resources
necessary to set and accomplish your goals. These professional traits will
help you successfully complete this distance training course.
Continued on next page
MCI Course 2515H
v
Study Guide, Continued
Beginning Your
Course
Before you actually begin this course of study, read the student information
page. If you find any course materials missing, notify your training officer or
training NCO. If you have all the required materials, you are ready to begin.
To begin your course of study, familiarize yourself with the structure of the
course text. One way to do this is to read the table of contents. Notice the
table of contents covers specific areas of study and the order in which they are
presented. You will find the text divided into several study units. Each study
unit is comprised of two or more lessons and lesson exercises.
Leafing
Through the
Text
Leaf through the text and look at the course. Read a few lesson exercise
questions to get an idea of the type of material in the course. If the course has
additional study aids, such as a handbook or plotting board, familiarize
yourself with them.
The First Study
Unit
Turn to the first page of study unit 1. On this page, you will find an
introduction to the study unit and generally the first study unit lesson. Study
unit lessons contain learning objectives, lesson text, and exercises.
Reading the
Learning
Objectives
Learning objectives describe in concise terms what the successful learner,
you, will be able to do as a result of mastering the content of the lesson text.
Read the objectives for each lesson and then read the lesson text. As you read
the lesson text, make notes on the points you feel are important.
Completing the
Exercises
To determine your mastery of the learning objectives and text, complete the
exercises developed for you. Exercises are located at the end of each lesson,
and at the end of each study unit. Without referring to the text, complete the
exercise questions and then check your responses against those provided.
Continued on next page
MCI Course 2515H
vi
Study Guide, Continued
Continuing to
March
Continue on to the next lesson, repeating the above process until you have
completed all lessons in the study unit. Follow the same procedures for each
study unit in the course.
Seeking
Assistance
If you have problems with the text or exercise items that you cannot solve,
ask your training officer or training NCO for assistance. If they cannot help
you, request assistance from your MCI distance learning instructor by calling
the Distance Learning Technologies Department’s Support Division at DSN
325-7516 or commercial (202) 685-7516, or log on to the MCI home page at
www.mci.usmc.mil/feedback/course developers.
Preparing for
the Final Exam
To prepare for your final exam, you must review what you learned in the
course. The following suggestions will help make the review interesting and
challenging.
•
CHALLENGE YOURSELF. Try to recall the entire learning sequence
without referring to the text. Can you do it? Now look back at the text to
see if you have left anything out. This review should be interesting.
Undoubtedly, you’ll find you were not able to recall everything. But with
a little effort, you’ll be able to recall a great deal of the information.
•
USE UNUSED MINUTES. Use your spare moments to review. Read
your notes or a part of a study unit, rework exercise items, review again;
you can do many of these things during the unused minutes of every day.
•
APPLY WHAT YOU HAVE LEARNED. It is always best to use the
skill or knowledge you’ve learned as soon as possible. If it isn’t possible
to actually use the skill or knowledge, at least try to imagine a situation in
which you would apply this learning. For example make up and solve
your own problems. Or, better still, make up and solve problems that use
most of the elements of a study unit.
Continued on next page
MCI Course 2515H
vii
Study Guide, Continued
Preparing for
the Final Exam,
continued
•
USE THE “SHAKEDOWN CRUISE” TECHNIQUE. Ask another
Marine to lend a hand by asking you questions about the course. Choose
a particular study unit and let your buddy “fire away.” This technique can
be interesting and challenging for both of you!
•
MAKE REVIEWS FUN AND BENEFICIAL. Reviews are good habits
that enhance learning. They don’t have to be long and tedious. In fact,
some learners find short reviews conducted more often prove more
beneficial.
Tackling the
Final Exam
When you have completed your study of the course material and are confident
with the results attained on your study unit exercises, take the sealed envelope
marked “FINAL EXAM” to your unit training NCO or training officer.
Your training NCO or officer will administer the final exam and return the
exam the answer sheet to MCI for grading. Before taking your final
examination, read the directions on the DP-37 answer sheet carefully.
Completing
Your Course
The sooner you complete your course, the sooner you can better yourself by
applying what you’ve learned! HOWEVER—you do have 2 years from the
date of enrollment to complete this course.
Graduating!
As a graduate of this distance training course and as a dedicated Marine, your
job performance skills will improve, benefiting you, your unit, and the Marine
Corps.
Semper Fidelis!
MCI Course 2515H
viii
STUDY UNIT 1
RADIO COMMUNICATIONS
Overview
Introduction
The radio is the principal means of communication in today’s tactical Marine
Corps. It is essential for not only command and control of the battlefield but
also for passing routine administrative information. Understanding how radio
waves travel or propagate will enhance your ability to establish
communications between locations separated by great distances and
obstacles.
Scope
This study unit discusses the basic building blocks common to all radios and
introduces radio waves and their characteristics.
In This Study
Unit
This study unit contains the following lessons:
Topic
Radio Sets and Waves
Carrier Waves and Modulation
MCI Course 2515H
1-1
See Page
1-3
1-13
Study Unit 1
(This page left intentionally blank.)
MCI Course 2515H
1-2
Study Unit 1
LESSON 1
RADIO SETS AND WAVES
Overview
Introduction
Before you can study the propagation of radio waves, you must learn the
origin of these waves, the radio set. The Marine Corps uses many types of
radios, ranging from small and manpacked versions to entire systems that
must be vehicular transported. To keep it simple, this lesson examines the
basic building blocks common to all radios.
Content
This lesson discusses the basic parts of a radio and what role each part plays
in the overall operation of the radio. Additionally, this lesson introduces you
to radio waves and discusses, in depth, the characteristics of radio waves,
such as frequency and wavelength.
Learning
Objectives
At the end of this lesson, you should be able to
•
State the purpose of a radio transmitter.
•
State the purpose of a radio receiver.
•
State what an antenna is used for.
•
State the purpose of a power supply.
•
Define radio waves.
•
State what determines the frequency of a radio wave.
•
State the formula used to find the wavelength when the frequency is
known.
Continued on next page
MCI Course 2515H
1-3
Study Unit 1, Lesson 1
Overview, Continued
In This Lesson
This lesson contains the following topics:
Topic
Overview
Basic Components
Electro-Magnetic Waves
Lesson 1 Exercise
MCI Course 2515H
1-4
See Page
1-3
1-5
1-6
1-10
Study Unit 1, Lesson 1
Basic Components
Parts of a
Radio
All radios, regardless of size or purpose are comprised of the following parts:
a transmitter, a receiver, an antenna, and a power supply.
Radio
Transmitter
A transmitter is a device that sends out radio signals. It generates, modulates,
and radiates a radio frequency (RF) signal. A transmitter consists of an RF
generator, a power amplifier for increasing the level of the signal to the
desired level, and a modulator responsible for superimposing the intelligence
onto the carrier.
Radio Receiver
The receiver uses highly selective filtering networks to extract the desired
electro-magnetic waves from the air. These signals are then amplified to a
useable level and the intelligence that was placed upon the carrier in the
modulation process is removed in the demodulation process. The
intelligence, whether it is voice or data, is then passed to the appropriate
portions of the radio for further processing.
Antenna
The antenna has a function in both the transmitting and receiving processes of
a radio. In the transmitting process, the antenna provides a means for
radiating the RF energy produced by the transmitter and power amplifier into
space. In the receiving process, the antenna intercepts or picks up the RF
signals radiated by the distant end radio.
Power Supply
Power supplies are devices that provide the voltage necessary to operate
electronic equipment. In most radios, the transmitter and receiver draw from
the same power supply, with the transmitter consuming the most of the
power. Power supplies vary in size and output depending on the
characteristics of the radio and can range from a small cell battery to a large
diesel engine generator.
MCI Course 2515H
1-5
Study Unit 1, Lesson 1
Electro-Magnetic Waves
Definition
Radio waves are electro-magnetic energy radiated from an antenna, as shown
in the diagram below. These waves travel near the surface of the earth and
also radiate skyward at various angles to the surface of the earth. These
electro-magnetic waves travel through space at the speed of light,
approximately 186,000 miles (300,000 kilometers) per second.
Wavelength
The term wavelength refers to the distance a radio wave travels in the period
of time required to complete one cycle. Each complete cycle of two
alternations of the wave is one wavelength expressed in meters. This
wavelength may be measured from the start of one wave to the start of the
next wave, as shown in the diagram below or from the crest of one wave to
the crest of the next wave. In either case, the distance is the same.
Continued on next page
MCI Course 2515H
1-6
Study Unit 1, Lesson 1
Electro-Magnetic Waves, Continued
Frequency
The frequency of a radio wave is the number of complete cycles that occur in
one second. The longer the time of one cycle, the longer the wavelength and
the lower the frequency. The shorter the time of one cycle, the shorter the
wavelength and the higher the frequency.
Since the frequency of a radio wave is very great, it is expressed in kilohertz
(KHz) or megahertz (MHz). One KHz is equal to 1,000 cycles per second
and one MHz is equal to 1,000,000 cycles per second. Compared in the
figure below are the wavelengths of a 2 MHz wave and that of a 10 MHz
wave.
Velocity
Simply stated, velocity is the speed at which a radio wave moves. It is
important to note that the velocity of a radio wave is relative to the diameter
and conductivity of the material it is traveling through. For instance, radio
waves travel faster through copper wire than they do through aluminum.
Continued on next page
MCI Course 2515H
1-7
Study Unit 1, Lesson 1
Electro-Magnetic Waves, Continued
Velocity
Example
For comparison purposes, consider two sound waves, one traveling through
free space and one traveling through water. The wave traveling through free
space encounters significantly less resistance and therefore can travel farther
and faster. At the relatively low speed of sound, these differences are
measurable. A million times faster; however, at the relative speed of a radio
wave, these speed variations become lost in obscurity. Therefore, for
practical purposes, the velocity of a radio wave is considered to be a constant
300 million meters per second, regardless of its frequency or amplitude. To
find the wavelength when the frequency is known, divide this constant
velocity by the frequency, as shown in the table below. Note that all three
equations are equivalent; however, the first uses the frequency in Hertz and
the following two use Kilohertz and Megahertz, respectively.
Wavelength (in meters) =
300,000,000 (meters per second)
frequency (cycles per second)
300,000
frequency (KHz)
300
frequency (MHz)
To find the frequency when the wavelength is known, divide the velocity by the
wavelength, as shown in the table below.
Frequency (cycles per
second)
Frequency (KHz)
300,000,000
wavelength (meters)
300,000
wavelength (meters)
300
wavelength (meters)
Frequency (MHz)
Continued on next page
MCI Course 2515H
1-8
Study Unit 1, Lesson 1
Electro-Magnetic Waves, Continued
Frequency Bands
of the Radio
Spectrum
Most tactical radio sets operate within the 1.5 MHz to 400 MHz portion of
the frequency spectrum. For convenience of study and reference, radio
frequencies are divided into the groups or bands of frequencies shown
below.
Band
Very Low Frequency (VLF)
Low Frequency (LF)
Medium Frequency (MF)
High Frequency (HF)
Very High Frequency (VHF)
Ultra High Frequency (UHF)
Super High Frequency (SHF)
Extremely High Frequency (EHF)
MCI Course 2515H
1-9
Frequency (MHz)
Below .03
Above .03 to .3
Above .3 to 3.0
Above 3.0 to 30
Above 30 to 300
Above 300 to 3,000
Above 3,000 to 30,000
Above 30,000 to 300,000
Study Unit 1, Lesson 1
Lesson 1 Exercise
Directions
Complete items 1 through 7 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
The purpose of a radio transmitter is to generate,
a.
b.
c.
d.
Item 2
Which is a function of a radio receiver?
a.
b.
c.
d.
Item 3
Modulates an RF signal
Radiates an RF signal
Demodulates an RF signal
Generates an RF signal
In the receiving process, an antenna’s purpose is to
a.
b.
c.
d.
Item 4
modulate, and radiate a radio frequency (RF) signal.
demodulate, and radiate a radio frequency (RF) signal.
modulate, and collect a radio frequency (RF) signal.
modulate, and amplify a radio frequency (RF) signal.
radiate RF energy into space.
demodulate received RF signals.
intercept RF signals radiated by the distant end radio.
extract the desired electro-magnetic waves from the air.
What is the purpose of a power supply?
______________________________________________________________
______________________________________________________________
Continued on next page
MCI Course 2515H
1-10
Study Unit 1, Lesson 1
Lesson 1 Exercise, Continued
Item 5
Define radio waves.
______________________________________________________________
______________________________________________________________
Item 6
What determines the frequency of a radio wave?
______________________________________________________________
______________________________________________________________
Item 7
Which mathematical calculation is used to find the wavelength when the
frequency of a radio wave is known?
a.
b.
c.
d.
MCI Course 2515H
Divide frequency by velocity
Multiply frequency by velocity
Divide velocity by frequency
Divide wavelength by velocity
1-11
Study Unit 1, Lesson 1
Lesson 1 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
a
2
c
3
c
4
Provides the voltage needed to operate
electronic equipment
5
Electro-magnetic energy radiated from an
antenna
6
The number of complete cycles that occur
in one second
7
c
Summary
Reference
1-5
1-5
1-5
1-5
1-6
1-7
1-8
In this lesson, you’ve learned about the purpose of a radio transmitter, a radio
receiver, an antenna, and a power supply. You have also learned about radio
waves, their wavelength and velocity, and the different bands of the radio
spectrum.
The next lesson shows you how radio waves are used to carry information.
MCI Course 2515H
1-12
Study Unit 1, Lesson 1
LESSON 2
CARRIER WAVES AND MODULATION
Overview
Introduction
When a radio operator speaks into a microphone or a Marine in the field
transmits an email, that information is known as intelligence. A radio wave
alone carries no intelligence and is known as a carrier wave. This lesson will
explain how the intelligence is affixed to the carrier wave on the transmitting
end and removed on the receiving end.
Content
This lesson introduces you to carrier waves, their function, and discusses how
they are modulated.
Learning
Objectives
After completing this lesson, you should be able to
In This Lesson
•
Define carrier wave.
•
State the process by which information is attached upon a carrier wave.
•
Define amplitude modulation.
•
Define frequency modulation.
•
Define digital modulation.
This lesson contains the following topics:
Topic
Overview
Carrier Waves
Amplitude Modulation
Frequency Modulation
Digital Modulation
Lesson 2 Exercise
MCI Course 2515H
1-13
See Page
1-13
1-14
1-15
1-16
1-18
1-20
Study Unit 1, Lesson 2
Carrier Waves
Explanation
The radio transmitter supplies to the antenna a high frequency alternating
current at a fixed level of intensity. This current is called the carrier wave or
carrier. The carrier wave alone, as shown below, does not convey
information, but acts as a medium for the transmission of information signal.
The actual information, which is contained in a signal wave, in the case of
analog communications and data stream in the case of digital
communications, must be superimposed upon the carrier.
Modulation
The process of superimposing the information upon the carrier is called
modulation. This process differs greatly between analog and digital
communication systems.
•
Analog communications: The modulation process varies or modifies
either the frequency or the amplitude of the carrier waveform.
•
Digital communications: The carrier wave is shifted to represent a stream
of 1’s and 0’s.
Amplitude modulation (AM), frequency modulation (FM), and digital
methods of modulation are all used in military radio communication systems.
When audio frequency (AF) signals are superimposed on the radio frequency
(RF) carrier, additional RF signals are generated. The additional frequencies
are equal to the sum and the difference of the audio frequencies and the radio
frequency involved.
Example
Assume that a 1,000 KHz carrier is modulated by a 1 KHz audio tone. Two
new radio frequencies are developed: one at 1,001 KHz (the sum of 1,000
and 1 KHz) and the other at 999 KHz (the difference between 1,000 and 1
KHz). If a complex audio signal is used instead of a single tone, two new
frequencies will be set up for each of the audio frequencies involved.
These new frequencies are called sidebands.
MCI Course 2515H
1-14
Study Unit 1, Lesson 2
Amplitude Modulation
Explanation
Amplitude modulation (AM) is defined as the variation of the RF power
output of a transmitter at an audio rate. The RF energy increases and
decreases according to the audio (sound) frequencies. Amplitude modulation
is the process of varying the power output of a transmitter as illustrated
below:
How It Is
Modulated
The RF carrier is modulated by a single audio tone in which two additional
frequencies are produced. These two new frequencies are equal to the sum
and the difference of the two original frequencies. The frequency higher than
the carrier frequency is the upper side frequency and the frequency lower than
the carrier frequency is the lower side frequency. When the modulating
signal is made up of complex tones, as in speech, each individual frequency
component of the modulating signal produces its own upper and lower side
frequencies. These side frequencies occupy a band of frequencies called
sidebands. The sideband that contains the sum of the carrier and modulating
frequencies is called the upper sideband. The sideband that contains the
difference of the carrier and the modulating frequencies is the lower sideband.
Bandwidth
The space that a carrier and its associated sidebands occupy in the frequency
spectrum is called a channel. In amplitude modulation, the width of the
channel (bandwidth) is equal to twice the highest modulating frequency.
Example: When a 5,000 KHz carrier is modulated by a band of frequencies
ranging from 200 to 5,000 cycles (.2 to 5 KHz), the upper sideband extends
from 5,000.2 to 5,005 KHz and the lower sideband extends from 4,999.8 to
4,995 KHz. The entire bandwidth—from 5,005 to 4,995 KHz—is 10 KHz,
which is twice the highest modulating frequency (5 KHz).
The intelligence of an amplitude-modulated signal exists solely in the
sidebands in which the amplitude varies according to the strength of the
modulating signal. Transmitters operating in the medium and high frequency
bands of the radio spectrum generally use amplitude modulation.
MCI Course 2515H
1-15
Study Unit 1, Lesson 2
Frequency Modulation
Explanation
In a frequency-modulated wave, the frequency varies instantaneously about
the unmodulated carrier frequency in proportion to the amplitude of the
modulating signal. Therefore, when the modulating signal increases in
amplitude, the carrier frequency increases instantaneously; when the
modulating signal level decreases, the frequency decreases. This fluctuation
is illustrated below:
How It Is
Modulated
In an FM wave, the amplitude of the modulating signal determines the extent
of departure of the instantaneous frequency from the center or rest frequency.
Thus, the instantaneous frequency can be made to deviate as much as desired
from the carrier frequency by changing the amplitude of the modulating
signal. Even though the modulation frequency is only a few kilohertz, this
deviation frequency may be as high as several hundred kilohertz. The
sideband pairs generated by frequency modulation are not restricted, as in
amplitude modulation, to the sum and difference between the highest
modulating frequency and the carrier.
Sidebands
The first pair of sidebands in an FM signal is the carrier frequency, plus and
minus the modulating frequency. Additional sideband pairs will appear at
each multiple of the modulating frequency.
Example: When a carrier of 1 MHz is frequency modulated by an audio
signal of 10 KHz, a host of equally spaced sideband pairs will form around
the carrier in a rippling fashion. These frequencies will be strongest at 999
KHz and 1,010 KHz, second strongest at 980 KHz and 1,020 KHz, third
strongest at 970 KHz and 1,030 KHz, and continuing in the same process.
Bandwidth
The placement of sidebands described above causes an FM wave, consisting
of a center frequency and a number of sideband pairs, to occupy a much
greater bandwidth than an AM wave. This rippling fashion also forces the
amplitude of the modulating signal from the center frequency component to
the sideband pairs.
Continued on next page
MCI Course 2515H
1-16
Study Unit 1, Lesson 2
Frequency Modulation, Continued
The
Transmitted
Signal
The FM signal leaving the transmitting antenna is constant in amplitude, but
varies in frequency according to the modulating signal. The signal, which
travels between the transmitting and receiving antennas, encounters natural
and manmade noises that cause amplitude variations in the signal. These
undesirable amplitude variations are amplified as the signal passes through
successive stages of the receiver until the signal reaches the limiter stage.
Limiting and
Demodulating
The limiter eliminates amplitude variations and passes the constant-amplitude
FM signal on to circuitry designed to detect variations in the frequency of an
RF wave. This portion of the receiver, known as the discriminator,
transforms the frequency variations of the signal into corresponding voltage
amplitude variations. These voltage variations are sent onto demodulating
circuits that reproduce the original signal in audio or data devices. This type
of modulation is common in the very high frequency band.
MCI Course 2515H
1-17
Study Unit 1, Lesson 2
Digital Modulation
Explanation
In today’s digital age, more and more Marine Corps communication
equipment generates a digital stream of 1’s and 0’s instead of the modulating
waves that we have discussed up to this point. The previous analog methods
of modulation shifted either the amplitude or the frequency of the carrier.
How It Is
Modulated
When a digital input is used to modulate the carrier, the phase of the carrier is
shifted. This type of modulation is known as phase shift keying (PSK). In
the diagram below, the carrier’s wave begins at 0, travels in the positive
direction, and eventually ends at 0.
For modulation purposes, this wave could be shifted by 90 degrees, causing
the wave to begin at 1, travel in a negative direction, and then finish the cycle
at 1. Such a wave in this state is illustrated in the diagram below:
Continued on next page
MCI Course 2515H
1-18
Study Unit 1, Lesson 2
Digital Modulation, Continued
How It Is
Modulated,
continued
Furthermore, this wave can be shifted another 90 degrees, to start at the 180
degree point on the graph and yet another 90 degrees, to start at the 270
degree point on the graph. These four distinctly different phases of the wave
are assigned individual numerical values that are reconstructed at the
receiving station to form the original stream of 1’s and 0’s. Hypothetical
numerical values assigned to each phase of the carrier wave are listed in the
table below:
Phase Shift in Degrees
0
90
180
270
The Finished
Product
MCI Course 2515H
Bit Value
00
01
10
11
Now apply the values above to the digitally modulated carrier shown below
and you will see how the original stream of 1’s and 0’s are recreated.
1-19
Study Unit 1, Lesson 2
Lesson 2 Exercise
Directions
Complete items 1 through 5 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
The wave upon which all information is attached or superimposed for
transmission defines the
a.
b.
c.
d.
Item 2
radio wave.
carrier wave.
propagated wave.
electro-magnetic wave.
When intelligence has been applied to a carrier, the carrier is said to be
a.
b.
c.
d.
amplified.
demodulated.
propagated.
modulated.
Item 3
The ______________ is the process of varying the RF power output of a
transmitter.
Item 4
The ______________ is the process of varying the frequency of the carrier
wave.
Item 5
The process of shifting the phase of the carrier wave defines
a.
b.
c.
d.
MCI Course 2515H
demodulation.
amplitude modulation.
frequency modulation.
phase shift keying.
1-20
Study Unit 1, Lesson 2
Lesson 2 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
b
2
d
3
amplitude modulation
4
frequency modulation
5
d
Summary
Reference
1-14
1-14
1-15
1-16
1-18
In this study unit, you’ve learned the basic components of a radio set, how
radio waves’ electro-magnetic energy is radiated from an antenna, and how
analog methods—amplitude, frequency, and digital—modulate a carrier
wave.
The next study unit will show you how the atmosphere plays a large part in
the propagation of radio waves.
MCI Course 2515H
1-21
Study Unit 1, Lesson 2
(This page intentionally left blank.)
MCI Course 2515H
1-22
Study Unit 1, Lesson 2
STUDY UNIT 2
PROPAGATION OF RADIO WAVES
Overview
Introduction
Radio communication is not the same at all hours of the day or at all times of
the year. Despite the fact that radio waves and the atmosphere above the
earth are invisible, the atmosphere plays an important role in radio
communications. Solar events, such as sunspots several million miles away,
have a direct effect on communications. Since propagation usually takes
place within the earth's atmosphere, it is necessary to establish a basic
understanding of the air around and above us.
Scope
This study unit discusses propagation of radio waves and how the three
different layers that make up the earth’s atmosphere effect propagation. This
study unit will also discuss ground wave, sky wave propagation, skip zones,
and how the ionosphere effects long distance sky wave transmissions.
Additionally, this study unit will cover the effect fading has on long distance
communications and the different propagation paths associated with the
different frequency ranges (bands).
In This Study
Unit
This study unit contains the following lessons:
Topic
The Atmosphere
Ground Waves and Sky Waves
Maximum Usable Frequency (MUF) and Lowest Usable
Frequency (LUF)
Fading
The Effects of Frequency on Wave Propagation
MCI Course 2515H
2-1
See Page
2-3
2-15
2-23
2-29
2-37
Study Unit 2
(This page left intentionally blank.)
MCI Course 2515H
2-2
Study Unit 2
LESSON 1
THE ATMOSPHERE
Overview
Introduction
The ionosphere is the most unique layer of the earth’s atmosphere.
Comprised of many, distinctly different layers, the ionosphere is the region of
the atmosphere that we must thoroughly understand to achieve effective
communications.
Content
This lesson covers the three major layers of the atmosphere, their
characteristics, and their location.
Learning
Objectives
At the end of this lesson, you should be able to
•
Describe the atmosphere.
•
Name the three layers that make up the atmosphere.
•
State the general effect the "D" region has on high frequency radio waves.
•
State the region that is ionized at all hours of day and night.
•
State what determines the range of long distance radio transmissions.
•
Name the two layers of the ionosphere with the highest level of
ionization.
•
Define critical frequency.
Continued on next page
MCI Course 2515H
2-3
Study Unit 2, Lesson 2
Overview, Continued
In This Lesson
This lesson contains the following topics:
Topic
Overview
The Earth’s Atmosphere
The Ionosphere
Ionosphere Characteristics
Variations of the Ionosphere
Lesson 1 Exercise
MCI Course 2515H
2-4
See Page
2-3
2-5
2-7
2-9
2-10
2-12
Study Unit 2, Lesson 2
The Earth’s Atmosphere
Introduction
Wave propagation deals with the properties and the nature of the atmosphere
through which radio waves must travel from the transmitting antenna to the
receiving antenna. The atmosphere is a gaseous mass that envelops the earth.
It is not uniform because it varies with the altitude, temperature, geographic
location, time of day or night, season, and year. Knowledge of the
composition and properties of the atmosphere aids in the solution of problems
that arise in planning radio communication paths and in predicting the
reliability of communications. The earth's atmosphere is divided into three
regions: the troposphere, the stratosphere, and the ionosphere. Refer to the
diagram below for an idea of their location and heights above the earth.
Continued on next page
MCI Course 2515H
2-5
Study Unit 2, Lesson 2
The Earth’s Atmosphere, Continued
Troposphere
The troposphere is that portion of the earth's atmosphere extending from the
surface of the earth to a height of approximately 6.8 miles. Within the
troposphere, the bending of radio waves by refraction causes the radio
horizon to exceed the optical horizon. Tropospheric refraction (reflection
caused by sudden changes in the characteristics of air in a lower atmosphere)
effects the received signal at distances beyond the radio horizon.
Stratosphere
The stratosphere is that portion of the earth's atmosphere lying between the
troposphere and the ionosphere, from 6.8 miles to 30 miles above the earth.
The temperature in this region is nearly constant.
Ionosphere
The ionosphere is that portion of the earth's atmosphere above the lowest
level at which ionization (splitting of molecules into positive and negative
charges or ions) of low pressure gases will effect the transmission of radio
waves. It extends from 30 to 250 miles above the earth. The ionosphere is
composed of several distinct layers in which ionization occurs at different
levels and intensities.
MCI Course 2515H
2-6
Study Unit 2, Lesson 2
The Ionosphere
Definition
The ionosphere is that portion of the earth's atmosphere containing ionized
gases. There are four distinct layers of the ionosphere. In the order of
increasing heights and intensities, they are the “D”, “E”, “F1”, and “F2”
layers. The four layers are present only during the day when the rays of the
sun are directed toward that portion of the atmosphere. During the night, the
“F1” and “F2” layers merge into a single “F” layer and the “D” and “E” layers
fade out. The actual number of layers, their heights above the earth, and their
relative intensity of internal ionization vary from hour to hour, day to day,
month to month, season to season, and year to year. The relative distribution
of these layers is shown in the diagram below:
Continued on next page
MCI Course 2515H
2-7
Study Unit 2, Lesson 2
The Ionosphere, Continued
"D" Region
The "D" region exists only during daylight hours and has little effect in
bending the path of high frequency radio waves. The main effect of the "D"
region is its ability to attenuate or decrease the intensity of high-frequency
waves when the transmission path lies in sunlit regions.
"E" Region
The "E" region is used during the day for high-frequency radio transmission
over distances greater than 1,500 miles. The intensity of this layer decreases
during the night, rendering it useless for radio transmissions.
"F" Region
The "F" region exists at heights up to 240 miles above the surface of the earth
and is ionized at all hours of the day and night. The "F" region is comprised
of two well-defined layers during the day and one during the night. At night,
the "F" layer lies at a height of about 170 miles and is useful for long-range
radio communication (over 1,500 miles).
"F1" and "F2"
Regions
During the day, air warmed by sunlight causes the "F" region to split into two
distinct layers, the "Fl" layer and the "F2" layer. The " F2" layer is the most
useful of all layers for long-range radio communication, even though the
degree of ionization varies appreciably from day to day as compared with
other layers.
MCI Course 2515H
2-8
Study Unit 2, Lesson 2
Ionosphere Characteristics
Critical
Frequency
Primarily the ionization density of each ionospheric layer determines the
range of long-distance radio transmission. The higher the frequency, the
smaller the radio waves, and a greater density of ionization is required to
refract the waves back to earth. The upper ("E" and "F") layers refract the
higher frequencies because they are the most highly ionized. The "D" layer,
which is the least ionized, does not refract frequencies above approximately
500 KHz. Thus, at any given time and for each ionized layer, there is an
upper frequency limit at which waves sent vertically upward are reflected
directly back to earth. This limit is called the critical frequency. Waves that
are directed vertically at frequencies higher than the critical frequency pass
through the ionized layer out into space. All waves directed to the ionosphere
at frequencies lower than the critical frequency are refracted back to the earth.
Critical Angle
Radio waves used in communication generally are directed to the ionosphere
at some oblique angle are called the angle of incidence. Waves at frequencies
above the critical frequency can be returned, if propagated at angles of
incidence lower than the critical angle. At the critical angle and any angle
larger than the critical angle, the wave will pass through the ionosphere if the
frequency is higher than the critical frequency. As the angle becomes
smaller, an angle is reached at which the wave is bent back to the earth by
refraction. The distance between the transmitting antenna and the point at
which the wave first returns is called the skip distance.
MCI Course 2515H
2-9
Study Unit 2, Lesson 2
Variations of the Ionosphere
Definition
The movements of the earth around the sun and changes in the sun's activity
contribute to ionospheric variations. There are two main classifications of
these variations:
•
•
Regular
Variations
Regular variations: predictable behavior of the sun
Irregular variations: abnormal behavior of the sun
The regular variations are divided into four classes:
Class
Daily
Seasonal
27-Day
11-Year
Irregular
Variations
The transient or momentary ionospheric variations, though unpredictable,
have important effects on radio propagation. Some of the major effects are:
•
•
•
•
Sporadic E
Predictable Behavior
The rotation of the earth
The north and south progression of the sun
The rotation of the sun on its axis
The average cycle of sunspot activity
Sporadic E
Sudden ionospheric disturbance
Ionosphere storms
Nuclear detonations
When it is excessively ionized, the "E" layer often completely blanks out
reflections from the higher layers. This effect may occur during the day or
night.
Continued on next page
MCI Course 2515H
2-10
Study Unit 2, Lesson 2
Variations of the Ionosphere, Continued
Sudden
Ionospheric
Disturbance
Sudden ionospheric disturbances (SID) are ionization abnormalities of the
"D" layer. The most common causes of these disturbances are solar
anomalies, such as sunspots or solar flares.
Ionosphere
Storms
These storms may last from several hours to several days, and usually extend
over the entire earth. During these storms, sky wave transmission above
approximately 1.5 MHz shows low intensity and is subject to a type of rapid
blasting and fading, known as flutter fading.
Sunspots
Sunspots are caused by magnetic storms on the surface of the sun and can last
for weeks. Sunspots that disappear from view behind the sun will often
predictably reappear two weeks later as that portion of the sun comes back
into view. Sunspots generally follow an 11-year cycle, but can vary daily.
Sunspots cause an increase in ionization that will allow the "E" and "F" layers
to refract higher frequencies while causing more absorption by the "D" layer.
Solar Flares
Solar flares are large, sudden releases of energy on the sun, which can last
from a few minutes to several hours. Usually occurring near sunspots, they
can have energy outputs equivalent to the explosion of a billion H-bombs.
Solar flares have both immediate and delayed effects on HF communications.
The immediate effect is a large increase of solar noise and the start of a SID.
These effects, like their originators, can last from a few minutes to several
hours. The delayed effects can occur from 30 minutes to 72 hours after the
solar flare, and include polar cap absorption and ionospheric storms.
In either case, the result is total absorption of all frequencies above 1 MHz,
causing receivers to go dead.
Nuclear Effects
MCI Course 2515H
The physical properties of the ionosphere can also be greatly altered during a
nuclear exchange. Intense dust clouds formed by surface bursts would cause
the "D" layer to become highly ionized from gamma ray radiation caused by
low altitude air defense bursts (10 to 35 miles). Bursts, especially those at
high altitude (greater than 250 miles) would damage unshielded radio
equipment through an effect known as electromagnetic pulse (EMP). Ground
wave communications between surviving equipment would be hindered in the
direction of surface bursts due to the great amount of dirt in the air and/or the
changes in electrical properties of the earth.
2-11
Study Unit 2, Lesson 2
Lesson 1 Exercise
Directions
Complete items 1 through 7 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
The __________________________________________ defines atmosphere.
Item 2
The _____________, _____________, and _____________ regions make up
the earth’s atmosphere.
Item 3
The "D" region of the ionosphere has little effect on which type of radio
waves?
a.
b.
c.
d.
Item 4
The "F" region of the ionosphere is
a.
b.
c.
d.
Item 5
Sky waves
Skip waves
Low frequency
High frequency
present only during daylight hours.
ionized at all hours of day and night.
comprised of three separate layers.
rendered useless during the night.
The range of long distance radio transmissions is determined by the ________
of each ionospheric layer.
a.
b.
c.
d.
height
location
temperature
ionization density
Continued on next page
MCI Course 2515H
2-12
Study Unit 2, Lesson 2
Lesson 1 Exercise, Continued
Item 6
Name the two layers of the ionosphere with the highest level of ionization.
______________________________________________________________
Item 7
Define critical frequency.
______________________________________________________________
______________________________________________________________
MCI Course 2515H
2-13
Study Unit 2, Lesson 2
Lesson 1 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
3
4
5
6
7
Summary
Answer
gaseous mass that envelops the earth
troposphere--stratosphere--ionosphere
d
b
d
The upper ("E" and "F") layers
The highest frequency at which waves
sent vertically upward are reflected
directly back to earth.
Reference
2-5
2-5
2-8
2-8
2-9
2-9
2-9
In this lesson, you’ve learned about the different layers that compose the
earth’s atmosphere, as well as the different layers of the ionosphere and their
characteristics.
In the next lesson, you will learn about ground waves and sky waves.
MCI Course 2515H
2-14
Study Unit 2, Lesson 2
LESSON 2
GROUND WAVES AND SKY WAVES
Overview
Introduction
Most people assume that radio waves simply travel through the air and that
the paths they take to reach their final destination are irrelevant. In the study
of radio wave propagation, it is important to realize that radio waves travel by
ground modes as well as sky modes. Additionally, it is important to
understand that within these two, distinctly different classes, there are several
other sub-classes.
Content
The lesson discusses how radio waves react when they encounter the surface
of the earth and the different parts of the earth’s atmosphere.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Define ground wave propagation.
•
Name the three components of a ground wave.
•
State what sky wave propagation depends upon.
•
Define skip zone.
This lesson contains the following topics:
Topic
Overview
Ground Wave Propagation
Sky Wave Propagation
Lesson 2 Exercise
MCI Course 2515H
2-15
See Page
2-15
2-16
2-17
2-20
Study Unit 2, Lesson 2
Ground Wave Propagation
Definition
Ground wave propagation refers to radio transmissions that do not utilize
waves that have been refracted from the ionosphere. The field intensity of
ground waves depends on the transmitter power, the characteristics of the
transmitting antenna, and the frequency of the waves. Additionally, the
diffraction of the waves around the curvature of the earth, the conductivity
and dielectric constant of the local terrain, the nature of the transmission path,
and local weather conditions also effect the intensity of ground waves. The
ground wave is comprised of three distinctly different components: the direct
wave, the ground-reflected wave, and the surface wave. The three
components are identified in the diagram at the bottom of this page.
Direct Wave
The direct wave is that component of the entire wave front that travels
directly from the transmitting antenna to the receiving antenna. This
component is limited to the line-of-sight distance between the transmitting
and receiving antennas, plus a small, additional distance caused by the
curvature of the earth. Increasing the height of the transmitting antenna or the
receiving antenna (or both) can extend this distance.
GroundReflected Wave
The ground-reflected wave is the portion of the radiated wave that reaches the
receiving antenna after being reflected from the surface of the earth. When
both the transmitting and receiving antennas are on or close to the ground, the
direct and ground-reflected components of the ground wave tend to cancel
each other out.
Surface Wave
The surface wave, which follows the curvature of the earth, is the component
of the ground wave that is effected by the conductivity and dielectric constant
of the earth.
MCI Course 2515H
2-16
Study Unit 2, Lesson 2
Sky Wave Propagation
Sky Wave
Transmission
Paths
Sky wave propagation refers to those types of radio transmissions that depend
on the ionosphere to provide signal paths between transmitters and receivers.
Sky wave transmissions are by far the most important method for long
distance radio communications. The various sky wave transmission paths are
identified in the diagram below:
Continued on next page
MCI Course 2515H
2-17
Study Unit 2, Lesson 2
Sky Wave Propagation, Continued
Sky Wave
Modes
The area where the wave returns to the earth depends on the height of the
ionized layer and the amount of bending the wave encounters while traversing
the layer. This bending is a function of the frequency of the wave as
compared to the ion density of the layer. Upon return to the earth's surface,
part of the energy enters the earth to be rapidly dissipated, but part is reflected
back into the ionosphere where it may reflect downward again at a still
greater distance from the transmitter. This means of traveling in hops,
bouncing between the ionosphere and the surface of the earth, is known as
multi-hop transmission and enables transmissions to be received at long
distances from the transmitter. The diagram below illustrates this means of
travel for paths involving one, two, or three reflections from the ionosphere
(single, double, and triple hop modes or paths).
Continued on next page
MCI Course 2515H
2-18
Study Unit 2, Lesson 2
Sky Wave Propagation, Continued
Skip Zone
MCI Course 2515H
The skip zone is that area where no usable signal can be received from a
given transmitter operating at a given frequency. This area is bounded by the
outer edge of the usable ground-wave propagation and the point nearest the
antenna at which the closest sky wave returns to earth. The greater the
distance between those two points, the larger the skip zone. Refer to the
diagram below for the skip zone and its relation to the ground wave. If the
ground wave extends to the point where skip waves begin, there is no skip
zone. In this case, both the sky wave and the ground wave may arrive at the
antenna with nearly the same field intensity, but at randomly different phases.
When this occurs, the sky wave component alternately reinforces and cancels
the ground wave component, causing blasting (during reinforcement) and
fading (during cancellation) of the signal.
2-19
Study Unit 2, Lesson 2
Lesson 2 Exercise
Directions
Complete items 1 through 4 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
Define ground wave propagation.
______________________________________________________________
______________________________________________________________
Item 2
What are the three components of the ground wave?
a.
b.
c.
d.
Item 3
Signal paths between the transmitter and receiver in sky wave propagation are
provided by the
a.
b.
c.
d.
Item 4
Ground wave, sky wave, and skip wave
Direct wave, ground refracted wave, and skip wave
Direct wave, ground reflected wave, and surface wave
Direct wave, ground wave, and sky wave
troposphere.
ionosphere.
atmosphere.
stratosphere.
Define the skip zone.
______________________________________________________________
______________________________________________________________
MCI Course 2515H
2-20
Study Unit 2, Lesson 2
Lesson 2 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
Radio transmissions that do not make use
of waves that have been refracted from the
ionosphere.
2
c
3
b
4
An area where no usable signal can be
received from a given transmitter
operating at a given frequency
Summary
Reference
2-16
2-16
2-17
2-19
In this lesson, you’ve learned about ground waves and sky waves.
In the next lesson, you will learn about the maximum usable frequency
(MUF) and the lowest usable frequency (LUF).
MCI Course 2515H
2-21
Study Unit 2, Lesson 2
(This page is intentionally left blank.)
MCI Course 2515H
2-22
Study Unit 2, Lesson 2
LESSON 3
MAXIMUM USUABLE FREQUENCY (MUF) AND LOWEST
USABLE FREQUENCIES (LUF)
Overview
Introduction
From the previous lessons, it is apparent that the frequency of a radio wave
plays a large part in how well the sky wave propagates. In some cases,
however, if the frequency of the wave is too high or too low, that wave will
not propagate at all. Knowing the frequency limits will aid in frequency
selection and make sure communications are effective.
Content
This lesson discusses the employment of previously discussed principles to
determine which frequencies are best suited for communications.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Define maximum usable frequency (MUF).
•
Describe what would happen to frequencies greater than the MUF.
•
Define lowest usable frequency (LUF).
This lesson contains the following topics:
Topic
Overview
Maximum Usable Frequency (MUF)
Lowest Usable Frequency (LUF)
Lesson 3 Exercise
MCI Course 2515H
2-23
See Page
2-23
2-24
2-26
2-27
Study Unit 2, Lesson 3
Maximum Usable Frequency (MUF)
Definition
An important concept associated with sky wave propagation is called the
maximum usable frequency (MUF). The MUF is the highest frequency at
which a radio wave will reflect from an ionospheric layer for a given
elevation or propagation path. Frequencies higher than the MUF will
penetrate the layer and escape into space. The diagram below depicts a chart
used to determine specific frequencies and their usefulness depending on the
time of day.
Continued on next page
MCI Course 2515H
2-24
Study Unit 2, Lesson 3
Maximum Usable Frequency (MUF), Continued
Predictions
It is important at this point to discuss propagation predictions and their
statistical nature. The science of predicting ionospheric conditions and
selecting frequencies to use for a given path is well developed, but subject to
the same accuracy problems as prediction of the local weather. It is
impossible to predict with
•
Absolute accuracy the best choice of frequency to use for a given
propagation path.
•
Reasonable accuracy what the MUF will be for a given communication
path at a particular time of day.
These predictions are usually based on a statistical reliability of 50 percent.
Example
Assume the MUF for a certain propagation path is predicted to be 12 MHz
during the time period of 1200 to 1500 hours for the month of November.
This actually means the MUF will be lower than 12 MHz 15 days of the
month and higher than 12 MHz the other 15 days of the month. The median
MUF for the entire month will be 12 MHz. It also means that on a given day
when the MUF is actually 12 MHz, frequencies slightly higher than 12 MHz
may be used with greatly reduced reliability.
Frequency
Selection
When there is a choice of frequencies to use, it is always best to use a higher
frequency. This is especially true when communicating over distances greater
than 650 miles. This reduces absorption from any lower layer and minimizes
multi-path fading. However, it is generally undesirable to operate at or near
the MUF since this frequency is reflected only 50 percent of the time. To
allow for day-to-day changes in the MUF and the critical frequency, it is
customary to use a frequency that is about 85 percent of the MUF. This lower
frequency is known as the frequency of optimum transmission (FOT). It is
based on the statistical fact that the FOT lies below the daily variations of the
actual MUF about 90 percent of the time. It is not always the frequency for
minimum path loss or for minimum fading, and there are times when a
frequency 10 percent lower or higher than the FOT will be more reliable.
Based on statistics, the FOT represents the best choice for a given path length,
time of day, season, and sunspot number.
MCI Course 2515H
2-25
Study Unit 2, Lesson 3
Lowest Usable Frequency (LUF)
Definition
As the frequency for transmission over any given sky wave path is increased,
a value will be reached at which the radio signal just overrides the level of
atmospheric and other radio noises. This is called the lowest usable
frequency (LUF) because frequencies lower than the LUF are too weak for
useful communications. For a given transmitter power as the operating
frequency is decreased, the average signal level at the receiver will decrease
due to increased ionospheric absorption. The average level of natural
atmospheric noise (lightning discharge) and manmade noise (electrical
equipment) existing in the vicinity of the receiver increases at lower
frequencies. Thus, if the frequency of transmission is reduced much below
the critical frequency, the received signal strength decreases while the
received noise increases until finally the signal is generally unusable.
Frequency
Selection
The LUF depends upon the power of the transmitter, path loss, total noise
level at the receiving location, receiving antenna gain and directivity, and
noise generated within the receiver itself. Because ionospheric absorption is
highest when the "D" layer reaches its peak, the LUF generally peaks around
noon. A frequency for day use must be chosen sufficiently above the LUF to
ensure a reliable signal-to-noise ratio.
MCI Course 2515H
2-26
Study Unit 2, Lesson 3
Lesson 3 Exercise
Directions
Complete items 1 through 3 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
Define maximum usable frequency (MUF).
______________________________________________________________
______________________________________________________________
Item 2
Waves of frequencies higher than that of the MUF will
a.
b.
c.
d.
Item 3
encounter high levels of atmospheric noise.
be most useful for daytime communications.
penetrate the ionosphere and escape into space.
be reflected by the "F" region of the ionosphere.
Define lowest usable frequency (LUF).
______________________________________________________________
______________________________________________________________
MCI Course 2515H
2-27
Study Unit 2, Lesson 3
Lesson 3 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
The highest frequency at which a radio wave
will reflect from an ionospheric layer for a
given elevation or propagation path.
2
c
3
The frequency at which the radio signal just
overrides the level of atmospheric and other
radio noises.
Summary
Reference
2-24
2-24
2-26
In this lesson, you’ve learned about the maximum usable frequency (MUF)
and the lowest usable frequency (LUF), and how these two principles can aid
in selecting the proper frequencies to enhance your ability to communicate.
In the next lesson, you will learn about a common obstruction to effective
communications known as fading.
MCI Course 2515H
2-28
Study Unit 2, Lesson 3
LESSON 4
FADING
Overview
Introduction
To this point, you have studied the modulated carrier wave, its origin, the
various paths the wave can take en route to the receiving station, and the
layers of the atmosphere the wave will encounter on its way to the receiving
end. Unfortunately, understanding and employing this knowledge is not
enough to ensure good communications. Many well-planned
communications exercises are plagued by a phenomenon known as fading.
Content
This lesson discusses fading and addresses the causes of this phenomenon.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Define fading.
•
Name the four types of fading.
This lesson contains the following topics:
Topic
Overview
Fading Loss
Types of Fading
Lesson 4 Exercise
MCI Course 2515H
2-29
See Page
2-29
2-30
2-31
2-34
Study Unit 2, Lesson 4
Fading Loss
Definition
When a radio signal is received over a long distance path, a periodic increase
and decrease of received signal strength may result. This phenomenon is
most common in the high frequency range. Most modern radios have internal
circuitry that eliminates the "blasting" caused by increased signal strength, so
this lesson will concentrate on the "fading" caused by decreased signal
strength.
Cause and
Prevention
The precise origin of fading is seldom understood. There is little common
knowledge of what precautions can be taken to reduce or eliminate the
troublesome effects of fading. Suggested methods for reducing fading are
•
Increase transmitter power and antenna gain
•
Use two or more receiving antennas spaced some distance apart with both
feeding into the same receiver (space diversity reception)
•
Select the proper frequency
•
Know the capabilities and limitations of the transmitting and receiving
equipment
Fading associated with sky wave paths is the greatest single detriment to
reliable communications.
MCI Course 2515H
2-30
Study Unit 2, Lesson 4
Types of Fading
Four Classes
The many types of fading can be categorized into four principal classes:
•
•
•
•
Interference
Polarization
Absorption
Skip
Most cases of rapid fading are caused by a combination of the first two types
while the latter two types normally cause gradual fading.
Interference
Fading
Interference fading is caused by phase interference of two or more waves
from the same source arriving at the receiver over slightly different paths. If
the paths are of different lengths and their relative lengths vary for some
reason, such as fluctuations in the height of the ionosphere layers, the relative
phases of the waves arriving over the different paths vary with time, causing
alternate reinforcement and cancellation of the field intensity. This concept is
illustrated in the diagram below. Because of irregularities in the ionosphere,
one downcoming sky wave is really the summation of a great number of
waves of small intensity and of random relative phases, and thus the resultant
field intensity can vary greatly.
Continued on next page
MCI Course 2515H
2-31
Study Unit 2, Lesson 4
Types of Fading, Continued
Polarization
Fading
Additional variation in the field intensity effecting the receiving antenna
occurs when the polarization of the downcoming wave changes in relation to
the polarization of the receiving antenna. This variation is called polarization
fading. The polarization of the downcoming sky wave is changing
constantly. This is due mainly to the combination of the two oppositely
polarized components—the ordinary and the extraordinary wave—at random
amplitudes and phases.
The polarization of the downcoming sky wave is generally elliptical.
Elliptical polarization means that as the wave travels along the signal path,
the electric and magnetic fields remain at right angles to each other and to the
direction of propagation, rotating about the signal path in a corkscrew
fashion. This results in random and constantly changing values of the
amplitude and orientation of the electric field with respect to the receiving
antenna. The state of polarization of sky waves varies more rapidly than the
higher frequency, which accounts in part for the rapid fading on the higher
frequencies.
Absorption
Fading
Absorption fading is caused by short-term variations in the amount of energy
lost from the wave because of absorption in the ionosphere. In general, the
time period of this type of fading is much longer than that of other types since
the ionospheric absorption usually changes slowly. In extreme cases, sudden
ionospheric disturbances can account for this type of fading, although it is
usually classified as an irregular disturbance rather than fading.
Another example of this type of fading is the reflection and absorption of
radio waves by objects close to the receiver, such as when a vehicle is passing
under a bridge or near a heavy steel structure and can no longer receive radio
signals. Radiation from wires, fences, and steel structures can cause an
interference pattern that is relatively fixed in space, and can be detected only
by moving the receiving equipment around the radiating structure. Therefore,
care must be exercised when selecting communication sites with nearby
structures that could produce these effects.
Continued on next page
MCI Course 2515H
2-32
Study Unit 2, Lesson 4
Types of Fading, Continued
Skip Fading
MCI Course 2515H
Skip fading is observed at places near the limit of the skip distance, and is
caused by the changing angle of refraction. Near sunrise and sunset when the
ionization density of the ionosphere is changing, the MUF for a given
transmission path may fluctuate about the actual operation frequency. When
the skip distance extends out past the receiving station, the received signal
level drops abruptly and then increases just as abruptly when the skip distance
moves back in. This may take place many times before conditions reach a
steady state.
2-33
Study Unit 2, Lesson 4
Lesson 4 Exercise
Directions
Complete items 1 and 2 by performing the action required. Check your
answer against that listed at the end of this lesson.
Item 1
Define fading.
______________________________________________________________
______________________________________________________________
Item 2
The four types of fading are interference, polarization,
a.
b.
c.
d.
MCI Course 2515H
absorption, and switch.
antenna, and skip.
absorption, and skip.
reflection, and skip.
2-34
Study Unit 2, Lesson 4
Lesson 4 Exercise
Solutions
The table below lists the solution to the exercise item. If you have any
questions about this item, refer to the reference page.
Item Number
Answer
1
The periodic increase and decrease of
received radio signal strength.
2
c
Summary
Reference
2-30
2-31
In this lesson, you’ve learned about fading as well as the most common
causes and effects of fading.
In the next lesson, you will learn how to select the appropriate type of
propagation for a given frequency.
MCI Course 2515H
2-35
Study Unit 2, Lesson 4
(This page intentionally left blank.)
MCI Course 2515H
2-36
Study Unit 2, Lesson 4
LESSON 5
THE EFFECTS OF FREQUENCY ON WAVE PROPAGATION
Overview
Introduction
Different frequencies behave differently depending on which methods of
propagation are employed. The principles that have been discussed in the
previous lessons have shown that some methods of propagation are unsuitable
for certain frequencies.
Content
Utilizing the principles discussed in the previous lessons, this lesson reveals
which methods of propagation work best for which frequency bands.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
State the types of propagation and which types are best for specific
frequency bands.
•
State the wave propagation that is extremely useful for communications at
the low frequency band.
•
State the wave propagation that is extremely useful for communications at
the medium frequency band.
•
State the wave propagation that is extremely useful for communications at
the high frequency band.
•
State the only wave propagation path that can be used for communications
at the ultra high frequency band.
This lesson contains the following topics:
Topic
Overview
Wave Propagation
Lesson 5 Exercise
MCI Course 2515H
2-37
See Page
2-37
2-38
2-39
Study Unit 2, Lesson 5
Wave Propagation
Definition
The effects of the atmospheric layers on wave propagation—as described in
the previous lessons—are complicated further by variations in frequency of
the transmitted wave. The propagation principles for frequencies at the low
end of the frequency spectrum are drastically different than those at the high
end of the spectrum. (For ease of identification, frequencies are usually
classified in the ranges shown on page 1-7). It is also important to remember
that radio waves travel by means of ground waves, sky waves, or a
combination of both.
Low
Frequency
At low frequencies (.03 to .3 MHz), the ground wave is extremely useful for
communication over greater distance. The ground wave signals are quite
stable and show little seasonal variation.
Medium
Frequency
In the medium-frequency band (.3 to 3.0 MHz), the range of the ground wave
varies from about 15 miles at the low end of the band to about 400 miles at
the high end. Sky wave reception is possible during day or night at any of the
lower frequencies in this band. At night, the sky wave gives reception at a
distance up to 8,000 miles.
High
Frequency
In the high-frequency band (3.0 to 30 MHz), the range of the ground wave
decreases with an increase in frequency and the sky waves are greatly
influenced by ionospheric conditions.
Very High
Frequency
In the very-high-frequency band (30 to 300 MHz), there is no usable ground
reflected and no surface wave, only a slight refraction of sky waves by the
ionosphere at the lower frequencies. The direct wave provides
communication if the transmitting and receiving antennas are elevated
sufficiently above the surface of the earth. Transmission over any greater
range is unpredictable and will last only for short periods of time because of
sporadic conditions in the ionosphere.
Ultra High
Frequency
In the ultra-high-frequency band (300 to 3,000 MHz), the direct wave must be
used for all radio transmissions. Communication is limited to a short distance
beyond the horizon. Lack of static and fading in these bands make line-ofsight reception very good. Highly directive antennas can be built into a space
to concentrate RF energy into a narrow beam, increasing the signal intensity.
MCI Course 2515H
2-38
Study Unit 2, Lesson 5
Lesson 5 Exercise
Directions
Complete items 1 through 5 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
What wave propagation is useful for communications at low frequencies?
a.
b.
c.
d.
Item 2
Ground wave
Sky wave
Direct wave
Skip wave
What two types of wave propagation are useful in the medium-frequency
band?
(1) ___________________________________________________________
(2) ___________________________________________________________
Item 3
What two types of wave propagation are available for use in the highfrequency band?
(1) ___________________________________________________________
(2) ___________________________________________________________
Item 4
What propagation wave or component of a propagation wave provides the
best communication in the very-high-frequency band?
a.
b.
c.
d.
Ground wave
Sky wave
Surface wave
Skip wave
Continued on next page
MCI Course 2515H
2-39
Study Unit 2, Lesson 5
Lesson 5 Exercise, Continued
Item 5
Which component of the ground wave provides the best communication in
the ultra-high-frequency band?
a.
b.
c.
d.
MCI Course 2515H
Sky wave
Skip wave
Ground wave
Direct wave
2-40
Study Unit 2, Lesson 5
Lesson 5 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
(1)
(2)
3
(1)
(2)
4
5
Summary
Answer
a
Ground wave
Sky wave
Ground wave
Sky wave
Reference
2-38
2-38
2-38
a
d
2-38
2-38
In this study unit, you’ve learned about the earth's atmosphere and the three
different layers that make up the atmosphere. You know about ground wave
and sky wave propagation, skip zones, and how the ionosphere effects long
distance sky wave transmissions. Additionally, you are able to recognize the
effect fading has on long distance communications and the different
propagation paths associated with the different frequency ranges.
In the next study unit, you will learn the general characteristics of antennas,
as well as some of the common Marine Corps antennas and different types of
field expedient antennas.
MCI Course 2515H
2-41
Study Unit 2, Lesson 5
(This page intentionally left blank.)
MCI Course 2515H
2-42
Study Unit 2, Lesson 5
STUDY UNIT 3
ANTENNAS
Overview
Introduction
This study unit identifies the functions of an antenna, the components of the
radiation field, and antenna polarization. It also discusses the polarization
requirements for various frequencies and the advantages afforded by using
either vertical or horizontal polarization.
Scope
This study unit also discusses the conventional field antennas used by the
Marine Corps and seven types of field expedient antennas. It covers various
types of transmission lines and standing waves.
In This Study
Unit
This study unit contains the following lessons:
Topic
Functions of an Antenna and Antenna Radiation
Antenna Polarization
Conventional Antennas
Field Expedient Antennas
Transmission Lines
MCI Course 2515H
3-1
See Page
3-3
3-11
3-21
3-33
3-47
Study Unit 3
(This page left intentionally blank.)
MCI Course 2515H
3-2
Study Unit 3
LESSON 1
FUNCTIONS OF AN ANTENNA AND ANTENNA RADIATION
Overview
Introduction
The study of antennas is essential to gain a complete understanding of radio
communication and other electronic systems. In such systems, energy in the
form of radio or electro-magnetic waves is generated by electronic equipment
and fed to an antenna by means of a transmission line. The antenna radiates
this energy at roughly the speed of light. Receiving antennas placed in the
path of the traveling wave absorb part of this energy and send it to the
receiving equipment by means of a transmission line.
Content
This lesson discusses the differences between transmit and receive antennas
and shows how these antennas propagate or collect radio waves. This lesson
also describes the different fields that are radiated by transmitting antennas.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
State the function of a transmitting antenna.
•
Identify which field is radiated beyond the transmitting antenna.
•
Name the two components that make up the radiation field.
•
Name the field that is formed from the electric and magnetic components
of the radiation field.
•
State the purpose of a receiving antenna.
This lesson contains the following topics:
Topic
Overview
Functions of an Antenna
Antenna Radiation
Lesson 1 Exercise
MCI Course 2515H
3-3
See Page
3-3
3-4
3-6
3-8
Study Unit 3, Lesson 1
Functions of an Antenna
Transmitting
The function of a transmitting antenna is to convert the output power
delivered by a radio transmitter into an electro-magnetic field that radiates
through space. Therefore, the transmitting antenna converts energy having
one form to energy having another form.
Direction of
Power
When power is delivered to an antenna, two fields are set up by the
fluctuating energy: one is the induction field that associates with the stored
energy and the other is the radiation field that moves out into space at nearly
the speed of light. At the antenna, the intensities of these fields are high and
proportional to the amount of power delivered to the antenna. However, at a
short distance from the antenna and beyond, only the radiation field remains.
Components of
Electromagnetic
Waves
The radiation field is composed of an electric component and a magnetic
component. The electric and magnetic fields (components) radiated from an
antenna form the electro-magnetic field; this field is responsible for the
transmission of electro-magnetic energy through free space. Thus, the radio
wave may be described as a moving electro-magnetic field having velocity in
the direction of travel, and with components of electric intensity and magnetic
intensity arranged at right angles to each other. This relationship is identified
in the diagram below:
Continued on next page
MCI Course 2515H
3-4
Study Unit 3, Lesson 1
Functions of an Antenna, Continued
Receiving
MCI Course 2515H
The receiving antenna reverses the energy conversion. The function of the
receiving antenna is to convert the electro-magnetic field into energy that is
delivered to a radio receiver. In transmitting, the antenna operates as the load
for the transmitter; in receiving, it operates as the signal source for the
receiver.
3-5
Study Unit 3, Lesson 1
Antenna Radiation
Patterns
The energy of radio signals radiated by an antenna from an electro-magnetic
field having a definite pattern depends on the type of antenna used. This
radiation pattern is used to show both range and directional characteristics of
an antenna. A vertical antenna theoretically radiates energy equally in all
directions. In practice, the pattern is usually distorted by nearby obstructions
or terrain features.
ThreeDimensional
The full or solid radiation pattern is a three-dimensional figure that looks
somewhat like a doughnut. A three-dimensional depiction of a quarter-wave
vertical antenna with the transmitting antenna in the center is shown below:
Continued on next page
MCI Course 2515H
3-6
Study Unit 3, Lesson 1
Antenna Radiation, Continued
Cross Sectional
Despite the aesthetic quality of a three-dimensional radiation pattern, the most
widely recognized method of illustrating radiation patterns is by plotting the
full pattern, showing only one particular plane. This type of pattern is
referred to as cross sectional and is shown below.
The top radiation pattern is that of a half-wave horizontal antenna one quarter
wavelength above the ground and the bottom pattern is that of a half-wave
horizontal antenna, one half wavelength above the ground.
MCI Course 2515H
3-7
Study Unit 3, Lesson 1
Lesson 1 Exercise
Directions
Complete items 1 through 5 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
The function of a transmitting antenna is to convert the transmitter output
power into a(n)
a.
b.
c.
d.
Item 2
Which of the two fields set up by fluctuating energy is radiated out into
space?
a.
b.
c.
d.
Item 3
Induction
Convection
Radiation
Electron
The radiation field is composed of a(n) _______________ component and a
_____________ component.
a.
b.
c.
d.
Item 4
electro-magnetic field.
induction field.
magnetic field.
radiation pattern.
induction--convection
electric--magnetic
induction--magnetic
induction--radiation
The electric and magnetic fields (components) radiated from an antenna form
the _______________ field.
a.
b.
c.
d.
radiation
magnetic
electro-magnetic
induction
Continued on next page
MCI Course 2515H
3-8
Study Unit 3, Lesson 1
Lesson 1 Exercise, Continued
Item 5
What is the purpose of a receiving antenna?
______________________________________________________________
______________________________________________________________
MCI Course 2515H
3-9
Study Unit 3, Lesson 1
Lesson 1 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
a
2
c
3
b
4
c
5
Converts the electro-magnetic field into
energy that is delivered to a radio receiver
Summary
Reference
3-4
3-4
3-4
3-4
3-5
In this lesson, you’ve learned about the roles of receiving and transmitting
antennas, radiation patterns, and the different radiated fields.
In the next lesson, you will learn about polarization.
MCI Course 2515H
3-10
Study Unit 3, Lesson 1
LESSON 2
ANTENNA POLARIZATION
Overview
Introduction
The previous lesson described a radio wave as a moving electro-magnetic
field having velocity in the direction of travel, and with components of
electric intensity and magnetic intensity arranged at right angles to each other.
This lesson expands upon that concept and shows how rotating that electromagnetic field or polarizing it can enhance communications.
Content
This lesson discusses the concept of antenna polarization, the two primary
types of propagation, and the advantages and applications of each type.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
State how the polarization of a radiated wave is determined.
•
Name the two types of antenna polarization.
•
Identify the antenna polarization to be used when working with medium
and low frequencies.
•
State why it is better to use horizontally polarized antennas at high
frequencies.
•
State what type of polarization should be used at very-high and ultra-high
frequencies.
This lesson contains the following topics:
Topic
Overview
Polarization
Polarization Selection
Benefits of Vertical Polarization
Benefits of Horizontal Polarization
Receiving Antennas
Lesson 2 Exercise
MCI Course 2515H
3-11
See Page
3-11
3-12
3-14
3-15
3-16
3-17
3-18
Study Unit 3, Lesson 2
Polarization
Definition
Polarization of a radiated wave is determined by the direction of the electric
field lines of force. The two types of polarization are vertical and horizontal.
Vertical
Polarization
If the electric field lines of force are at right angles to the surface of the earth,
the wave is vertically polarized. This concept is illustrated in the diagram
below:
Continued on next page
MCI Course 2515H
3-12
Study Unit 3, Lesson 2
Polarization, Continued
Horizontal
Polarization
If the electric field lines of force are parallel to the surface of the earth, the
wave is said to be horizontally polarized as shown in the diagram below:
Proper
Orientation
A single-wire antenna is used to extract energy from a passing radio wave.
Therefore, maximum reception results when the antenna is oriented so that it
lies in the same direction as the transmitting antenna, which subsequently
orients it to the electric-field component. Thus, a vertical antenna is used for
efficient reception of vertically polarized waves and a horizontal antenna is
used for the reception of horizontally polarized waves. In some cases, the
field rotates as the wave travels through space. Under these conditions, both
horizontal and vertical components of the field exist and the wave is said to
have elliptical polarization.
MCI Course 2515H
3-13
Study Unit 3, Lesson 2
Polarization Selection
Medium
and Low
Frequencies
At medium and low frequencies, ground wave transmission is used
extensively. For this reason, it is necessary to use vertical polarization.
Vertical lines of force are perpendicular to the ground, and the radio wave can
travel a considerable distance along the ground surface with a minimum
amount of attenuation (loss). Because the earth acts as a fairly good
conductor at low frequencies, horizontal lines of force are shorted out—
limiting the useful range of horizontally polarized waves.
High
Frequencies
At high frequencies with sky wave transmission, it makes little difference
whether horizontal or vertical polarization is used. The sky wave reflected by
the ionosphere, arrives at the receiving antenna elliptically polarized.
Therefore, the transmitting and receiving antennas can be mounted either
horizontally or vertically. Horizontal antennas are preferred because they can
be made to radiate effectively at high angles and have inherent directional
properties.
Very- and
Ultra-High
Frequencies
With frequencies in the very-high or ultra-high range, either horizontal or
vertical polarization is satisfactory. Since the radio wave travels directly from
the transmitting antenna to the receiving antenna, the original polarization
produced at the transmitting antenna is maintained throughout the travel of
the wave to the receiving antenna. Therefore, if a horizontal half-wave
antenna is used for transmitting, a horizontal antenna must be used for
receiving. If a vertical half-wave antenna is used for transmitting, a vertical
antenna must be used for receiving.
MCI Course 2515H
3-14
Study Unit 3, Lesson 2
Benefits of Vertical Polarization
Vehicular
Applications
Simple, vertical half-wave antennas can be used to provide omni-directional
communication that has the ability to communicate with a moving vehicle.
When antenna heights are limited to 10 feet or less, as in vehicular
installation, vertical polarization provides a stronger received signal at
frequencies up to about 50 MHz. From approximately 50 to 100 MHz, there
is only a slight improvement over horizontal polarization with antennas of the
same height. The difference in signal strength above 1100 MHz is negligible.
Over Water
For transmission over large bodies of water, vertical polarization is decidedly
better than horizontal when antennas are below approximately 300 feet at 30
MHz. You would only need 50 feet at 85 MHz and still lower at higher
frequencies. Therefore, an ordinary antenna at mast heights, such as 40 feet,
vertical polarization is advantageous for frequencies less than about 100
MHz.
Aircraft
Interference
Radiation using vertical polarization is less effected by reflections from
aircraft flying over the transmission path. With horizontal polarization, such
reflections cause variations in the received signal strength. This factor is
important in locations where aircraft traffic is heavy.
Broadcast
Interference
With vertical polarization, less interference is produced or picked up because
of strong VHF and UHF broadcast transmission and reception (television and
frequency modulation), all of which use horizontal polarization. This factor
is important when an antenna must be located in an urban area having several
television and commercial FM broadcast stations.
MCI Course 2515H
3-15
Study Unit 3, Lesson 2
Benefits of Horizontal Polarization
Bi-Directional
A simple horizontal half-wave antenna is bi-directional. This characteristic
can help minimize interference from certain directions. Additionally,
horizontal antennas are less apt to pick up man-made interference that is
polarized vertically.
Heavy Foliage
When antennas are located near dense forest, horizontally polarized waves
suffer lower losses than vertically polarized waves, especially above about
100 MHz.
Flexibility
Small changes in antenna location do not cause large variations in the field
intensity of horizontally polarized waves when antennas are located among
trees or buildings. When vertical polarization is used, a change of only a few
feet in the antenna location may have a considerable effect on the received
signal strength. This is the result of interference patterns that produce
standing waves in space when spurious reflections from trees or buildings
occur.
Since the interference patterns will vary even when the frequency is changed
by only a small amount, considerable distortion may occur when complex
types of modulation are used, as with television signals or with certain types
of pulse-modulation systems. Under these conditions, horizontal polarization
is preferred.
Compatibility
With
Transmission
Line
MCI Course 2515H
When simple half-wave antennas are used, the transmission line (usually
vertical) is less effected by a horizontally mounted antenna. Keeping the
antenna at right angles to the transmission line and using horizontal
polarization keep the line out of the direct field of the antenna. As a result,
the radiation pattern and electrical characteristics of the antenna are
practically not effected by the presence of the vertical transmission line.
3-16
Study Unit 3, Lesson 2
Receiving Antennas
Vertical
Antennas
Vertical receiving antennas accept radio signals equally from all horizontal
directions, just as vertical transmitting antennas radiate equally in all
horizontal directions. Because of this characteristic, other stations operating
on the same or adjacent frequencies may interfere with the desired signal and
make reception difficult or impossible. However, reception of a desired
signal can be improved by using directional antennas.
Horizontal
Antennas
Horizontal half-wave antennas accept radio signals from all directions, except
signals originating in direct line with the ends of the antenna. When only one
signal is causing interference or when several interfering signals are coming
from the same direction, interference can be eliminated or reduced by
changing the antenna position so that either end of the antenna points directly
at the interfering station.
MCI Course 2515H
3-17
Study Unit 3, Lesson 2
Lesson 2 Exercise
Directions
Complete items 1 through 9 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
What determines the polarization of a radiated wave?
a.
b.
c.
d.
Item 2
The two types of antenna polarization are ___________ and
a.
b.
c.
d.
Item 3
transmitting--receiving.
induction--electro-magnetic.
horizontal--electrical.
horizontal--vertical.
What kind of antenna polarization should you use when working with
medium and low frequencies?
a.
b.
c.
d.
Item 4
The frequency of the transmitted wave
The impedance match of the transmission line
The direction of the electric field lines of force
The direction of the receiving station
Induction
Horizontal
Electrical
Vertical
Why is it better to use horizontally polarized antennas at high frequencies?
______________________________________________________________
______________________________________________________________
Continued on next page
MCI Course 2515H
3-18
Study Unit 3, Lesson 2
Lesson 2 Exercise, Continued
Item 5
Which types of polarization should be used at very-high and ultra-high
frequencies?
______________________________________________________________
Item 6 Through
Item 9
MCI Course 2515H
Matching: For items 6 through 9, match the polarization benefit in column 1
to the type of polarization in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Polarization Benefit
Type of Polarization
___ 6. Minimizes interference
from certain directions
___ 7. Provides the ability to
communicate with a
moving vehicle
___ 8. Somewhat less effected by
aircraft flying over the
transmission path
___ 9. Suffers lower losses when
located near dense forests
a. Vertical
b. Horizontal
3-19
Study Unit 3, Lesson 2
Lesson 2 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
3
4
5
6
7
8
9
Summary
Answer
c
d
d
They can be made to radiate effectively at
high angles and have inherent directional
properties.
Vertical or horizontal
b
a
a
b
Reference
3-12
3-12
3-14
3-14
3-14
3-16
3-15
3-15
3-16
In this lesson, you’ve learned about horizontal and vertical polarization and
the advantages of each.
In the next lesson, you will learn about conventional antenna systems
currently in use in the Marine Corps.
MCI Course 2515H
3-20
Study Unit 3, Lesson 2
LESSON 3
CONVENTIONAL ANTENNAS
Overview
Introduction
Conventional antennas are antennas manufactured to operate in certain
frequency ranges. These versatile antennas are normally sought after by the
Marine Corps for their ability to be fielded individually or as a component of
an existing communication system.
Content
This lesson introduces you to the most common conventional antennas in the
Marine Corps arsenal, the AS-2259/GR and the OE-254/GRC.
Learning
Objectives
At the end of this lesson, you should be able to
• Describe the antenna system AS-2259/GR.
• Describe the antenna system OE-254/GRC.
• State the purpose of the balun on the OE-254/GRC antenna system.
In This Lesson
This lesson contains the following topics:
Topic
Overview
Antenna System AS-2259/GR
Antenna System OE-254/GRC
Lesson 3 Exercise
MCI Course 2515H
3-21
See Page
3-21
3-22
3-25
3-29
Study Unit 3, Lesson 3
Antenna System AS-2259/GR
Definition
The AS-2259/GR manpack, HF antenna is essentially a dipole antenna fed
with a low-loss, foam-dielectric, coaxial mast that also serves as a support
structure. The dipole system uses a set of crossed sloping dipoles positioned
at right angles to each other. Physically, the antenna consists of eight
lightweight coaxial mast sections and four radiating elements that also serve
as guy lines. The antenna is transported in a canvas pack similar to a tool roll.
The total packed weight of the antenna is 14.7 pounds. Two Marines can
erect this antenna in 5 minutes without the use of any tools. The antenna is
shown in the diagram below:
Continued on next page
MCI Course 2515H
3-22
Study Unit 3, Lesson 3
Antenna System AS-2259/GR, Continued
How It Works
The AS-2259/GR antenna is designed to provide high-angle radiation (near
vertical incidence) to permit short-range sky wave propagation over
communication circuits ranging from 0 to 300 miles. The AS-2259/GR may
be used with tactical HF radios that tune a 15-foot whip antenna such as the
AN/GRC-193 or AN/MRC-138. The frequency range of the antenna is 2.0 to
12.0 MHz and maximum RF power capacity is 100 watts pep or average.
Electrical
Characteristics
Electrical characteristics for the AS-2259/GR are listed in the table below.
Personnel should become thoroughly familiar with data and procedures
contained in the entire instruction manual before working with this antenna.
Item
Frequency range
Polarization
RF power capacity
Input impedance
Electrical Characteristics
2.0 to 12.0 MHz
Horizontal and vertical simultaneously
100 watts pep or average
Compatible with output of radios using
15-foot whips such as the AN/PRC-104
Radiation pattern
Azimuth
Elevation
Gain
Omni-directional
Near vertical incidence
Similar to a dipole mounted horizontally
10 feet above the same type ground
Continued on next page
MCI Course 2515H
3-23
Study Unit 3, Lesson 3
Antenna System AS-2259/GR, Continued
Physical
Characteristics
Physical characteristics for the AS-2259/GR are listed in the table below.
Personnel should become thoroughly familiar with data and procedures
contained in the entire instruction manual before working with this antenna.
Item
Wind and ice
Height erected
Land area required
Erection time
Physical Characteristics
Survives 60-mph wind with no ice
15 feet
60 by 60 feet
Two Marines: 5 minutes
One Marine: 15 minutes
Less than 14.7 pounds
Packed weight
Ancillary
Equipment
A description of the ancillary equipment accompanying the AS-2259/GR is
listed in the table below.
Military Type Number
AS-2259/GR
MX-9313/GR
More
Information
MCI Course 2515H
Description of Equipment
An antenna that may be used directly
with HF manpack radios that tune a 15foot whip antenna such as the AN/PRC104. The antenna is rated at 100 watts
pep or average RF power.
An adapter for mounting the antenna on
vehicles or shelters equipped with HF
radios. Adapts antenna AS-2259/GR to
the AN/MRC-138 and similar radios
employing 1-inch, 8 threads per inch
whip bases and automatic couplers.
For more information on antenna system AS-2259/GR, see TM-07508A-14 or
MCI 2532, HF/UHF Field Radio Equipment.
3-24
Study Unit 3, Lesson 3
Antenna System OE-254/GRC
Definition
Antenna group OE-254/GRC is an omni-directional, biconical antenna
designed for broadband operation without field adjustment from 30 to 88
MHz, up to 350 watts.
The OE-254/GRC is intended for use with Marine Corps VHF radios such as
the AN/PRC-119A, AN/VRC-88 through 90, and the AN/MRC-145A as well
as similar radios operating between 30 and 88 MHz.
Components
The OE-254/GRC components are listed below:
•
Antenna AS-3166/GRC
• Feedcone assembly
• Balun assembly
• Antenna elements
• Mast AB-1244/GRC
• Cable assembly CG-1889C/U
Mechanical
Assembly
The feedcone assembly mounts the six antenna elements and the balun
assembly, which provides for mechanical connection to the mast by use of an
insulating extension.
Electrical
Assembly
The balun assembly is connected electrically to the radio set using the cable
assembly, and elevated up to 31 feet and 2 inches using the mast assembly.
The extended radials that make up the antenna elements are copper plated,
painted tubes of high-strength steel that are screwed together and then
screwed into a central balun.
Transport
The equipment is designed for hand or vehicular transportation. When
disassembled, the above mentioned items and their associated stakes, guy
lines and rings, hammer and baseplate are stowed in a roll type transit bag.
Continued on next page
MCI Course 2515H
3-25
Study Unit 3, Lesson 3
Antenna System OE-254/GRC, Continued
Diagram
The assembled OE-254/GRC is shown in the diagram below:
Continued on next page
MCI Course 2515H
3-26
Study Unit 3, Lesson 3
Antenna System OE-254/GRC, Continued
How it Works
The antenna itself consists of three upward and three downward extended
radials that simulate two cones that are electrically above ground, making the
overall antenna balanced. The extended radials project from the balun at an
angle of 30 degrees from true vertical as shown in the diagram on the
previous page.
Impedance
Matching
The nominal impedance of this biconical antenna is 200 ohms requiring the
use of a balun transformer to match this balanced impedance to the 50 ohm
unbalanced output impedance of the radio to which the AS-3166/GRC is
connected. The impedance transformation is accomplished on the AS3166/GRC through the 4 to 1 balun (balanced to unbalanced) transformer
attached between the two cones.
Mast
Construction
The mast consists of five upper and five lower mast sections, and a mast and
base assembly rising to a height of approximately 28 feet 3 inches. Each mast
section has a female and male end that permits the sections to be fitted
together.
Electrical
Characteristics
Electrical characteristics for the OE-254/GRC are listed in the table below.
Personnel should become thoroughly familiar with data and procedures
contained in the entire instruction manual before working with this antenna.
Item
Frequency range
Polarization
RF power capacity
Input impedance
Radiation pattern
Electrical Characteristics
30.0 to 88.0 MHz
Horizontal and vertical simultaneously
350 watts nominal
50 ohms
Non-directional
Continued on next page
MCI Course 2515H
3-27
Study Unit 3, Lesson 3
Antenna System, OE-254/GRC, Continued
Physical
Characteristics
Physical characteristics for the OE-254/GRC are listed in the table below.
Personnel should become thoroughly familiar with data and procedures
contained in the entire instruction manual before working with this antenna.
Item
Height erected
Land area required
Erection time
Packed weight
More
Information
MCI Course 2515H
Physical Characteristics
39 feet and 3 inches
80 by 80 feet
One Marine: 15 minutes
Approximately 42 pounds
For more information on the OE-254/GRC, see TM-11-5985-357-13.
3-28
Study Unit 3, Lesson 3
Lesson 3 Exercise
Directions
Complete items 1 through 8 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
The AS-2259/GR makes use of short-range sky wave propagation to
communicate over distances ranging from __________ miles.
a.
b.
c.
d.
Item 2
What is the maximum input power of the OE-254/GRC?
a.
b.
c.
d.
Item 3
0 to 150
0 to 200
0 to 250
0 to 300
300 watts
350 watts
400 watts
3,500 watts
What is the purpose of the balun on the OE-254/GRC?
______________________________________________________________
______________________________________________________________
Continued on next page
MCI Course 2515H
3-29
Study Unit 3, Lesson 3
Lesson 3 Exercise, Continued
Item 4 Through
Item 8
MCI Course 2515H
Matching: For items 4 through 8, match the antenna characteristic in column
1 to the antenna system in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Antenna Characteristic
Antenna System
___ 4. Operates in a VHF range
between 30 and 88 MHz
___ 5. An omni-directional, biconical
antenna
___ 6. Utilizes four radiating elements
that serve as guy lines
___ 7. Operates in a HF range
between 2 and 12 MHz
___ 8. Radiating elements are steel
tubes that are screwed together
into a central balun
a. AS-2259/GR
b. OE-254/GRC
3-30
Study Unit 3, Lesson 3
Lesson 3 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
d
2
b
3
To match the unbalanced, 50 ohm
impedance of VHF radio equipment to the
balanced, 200 ohm impedance of the
biconical antenna array
4
b
5
b
6
a
7
a
8
b
Summary
Reference
3-23
3-27
3-27
3-27
3-25
3-22
3-23
3-25
In this lesson, you’ve learned about the AS-2259/GR and the OE-254/GRC
antenna systems.
In the next lesson, you will learn about field expedient antennas that can be
constructed using simple materials.
MCI Course 2515H
3-31
Study Unit 3, Lesson 3
(This page left intentionally blank.)
MCI Course 2515H
3-32
Study Unit 3, Lesson 3
LESSON 4
FIELD EXPEDIENT ANTENNAS
Overview
Introduction
Sometimes an antenna manufactured to operate across a wide spectrum of
frequencies is not efficient enough to accomplish the mission at hand, or too
cumbersome to carry or set up. At these times, the field Marine can benefit
from an antenna custom built to operate at a specific frequency, an antenna
that takes into consideration key factors such as terrain, and time.
Content
This lesson introduces you to actual field expedient antennas that can be
constructed using the materials and instructions found in Appendix A.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Identify the different kinds of field expedient antennas.
•
State how to obtain optimum performance from a long wire antenna.
•
State what happens to a half-rhombic antenna when terminated in a
resistor.
•
State the length for which the vertical and ground plane elements for an
expedient ground plane antenna should be cut.
This lesson contains the following topics:
Topic
Overview
Half-Wave Dipole
Two-Element Yagi
Long Wire Antenna
Half-Rhombic Antenna
Sloping “V” Antenna
Vertical Quarter Wave Whip Antenna
Field Expedient Ground Plane Antennas
Lesson 4 Exercise
MCI Course 2515H
3-33
See Page
3-33
3-34
3-36
3-37
3-39
3-40
3-41
3-42
3-43
Study Unit 3, Lesson 4
Half-Wave Dipole
Characteristics
The half-wave dipole antenna shown in the diagram below consists of two
conductors, each a quarter wavelength, separated in the middle by an
insulator. The feed lines are connected to the two separated conductors. The
antenna is then supported along a straight line by means of ropes tied from the
ends of the antenna to supporting structures such as buildings, trees, poles,
etc. Current is maximum at the center and minimum at the ends. Voltage is
maximum at the ends and minimum at the center.
Continued on next page
MCI Course 2515H
3-34
Study Unit 3, Lesson 4
Half-Wave Dipole, Continued
Radiation
Pattern
The half-wave dipole antenna can be mounted in either a vertical, horizontal,
or diagonal position. Its radiation pattern is pictured in the diagram below,
where the antenna shown is positioned vertically. Maximum radiation is
perpendicular to the antenna axis. Since there is no radiation from the ends of
the antenna, a figure-8-type pattern is present in the vertical plane. Thus, the
antenna is bi-directional in the vertical plane. As shown, radiation is constant
in any direction in the horizontal plane. Mounting the antenna horizontally
would reverse the pattern illustrated below.
Construction
Instructions for constructing this antenna can be found in Appendix A, Biand Uni-Directional Antenna Construction.
Continued on next page
MCI Course 2515H
3-35
Study Unit 3, Lesson 4
Two-Element Yagi
Characteristics
This configuration may be new to most communicators. As seen in the
diagram below, this antenna consists of a reflecting element (a single wire)
mounted one quarter-wavelength behind a dipole antenna. This additional
element substantially increases the gain and makes the antenna more
directional.
Construction
Instructions for constructing this antenna can be found in Appendix A, Biand Uni-Directional Antenna Construction.
MCI Course 2515H
3-36
Study Unit 3, Lesson 4
Long Wire Antenna
Characteristics
The long wire antenna shown in the diagram below is a single wire, two to six
wavelengths long, suspended one-half wavelength above the ground.
Compared to other field expedient antennas, the long wire antenna has greater
gain and directivity. This high gain, coupled with the low elevation angle of
its main radiation lobe, makes the long horizontal wire antenna one of the
simplest antennas to erect.
The long wire antenna is capable of spanning distances in excess of 70 miles
and is one of the most practical antennas for use against jamming. The long
wire antenna is bi-directional or uni-directional.
Radiation
Pattern
The radiation pattern of a long wire antenna is comprised of a series of lobes
as shown in the diagram below. As a result of this lobe pattern, best
performance is obtained by directing a major lobe toward the intended
receiver.
Continued on next page
MCI Course 2515H
3-37
Study Unit 3, Lesson 4
Long Wire Antenna, Continued
Alignment
To properly align the long wire antenna to the distant station add or subtract
the wave angle according to the table below. Keep in mind the wave angle is
dependent upon the length of the antenna, as well as the operating frequency.
Offset Angle for the Long Wire Antenna
Freq (MHz)
10
12
14
16
18
20
24
30
Construction
MCI Course 2515H
Wire Length (Meters)
10
20
40
80 150
43° 27° 16°
55° 38° 23° 13°
51° 35° 21°
49° 31° 19°
47° 29° 17°
43° 27° 16°
55° 38° 23°
50° 33° 20°
Height (Meters)
30.0
25.0
21.4
18.7
16.7
15.0
12.5
10.0
Instructions for constructing this antenna can be found in Appendix A, Biand Uni-Directional Antenna Construction.
3-38
Study Unit 3, Lesson 4
Half-Rhombic Antenna
Characteristics
The half-rhombic antenna shown below is a terminated vertical antenna that
resembles an obtuse angle "V" antenna. With the half-rhombic antenna, an
unbalanced transmission line and a ground or counterpoise is used. As a
result, a vertically polarized radio wave is produced and the antenna is bidirectional. The antenna can be made to be uni-directional by connecting a
resistor of about 500 ohms between the far end of the antenna and the ground.
Dimensions
The typical military half-rhombic antenna consists of a 100-foot antenna wire
erected over a single 30-foot wooden mast and an 85-foot counterpoise wire
placed under the antenna about one foot off the ground and attached to both
ends of the antenna.
Construction
Instructions for constructing this antenna can be found in Appendix A, Biand Uni-Directional Antenna Construction.
MCI Course 2515H
3-39
Study Unit 3, Lesson 4
Sloping "V" Antenna
Characteristics
The sloping "V" antenna shown in the diagram below consists of downward
sloping long wires arranged to form a "V" and is fed with current of opposite
polarity. Major lobes from each wire combine in such a way that maximum
radiation occurs in the direction of a lobe that bisects the angle of the legs.
The pattern is basically bi-directional along the lines bisecting the angle,
producing primarily sky waves.
Gain
As the leg length of this antenna increases, so does the gain. The gain
(increase in effective power or performance) of a "V" antenna is almost
double that of a single long wire, since the radiation from the lobes of two
waves combine, reinforcing one another. To optimize this reinforcement, use
the table found in Appendix A to make sure the accuracy of the apex angle
(top angle where the radiating elements meet the mast section).
Directivity
The directivity of this antenna also increases with leg length. For maximum
efficiency, the legs of the "V" antenna should be cut to three wavelengths at
the center frequency of the desired band. The antenna can be made more
directional by terminating the individual legs with 500-ohm resistors.
Construction
Instructions for constructing this antenna can be found in Appendix A, Biand Uni-Directional Antenna Construction.
MCI Course 2515H
3-40
Study Unit 3, Lesson 4
Vertical Quarter Wave Whip Antenna
Characteristics
The vertical whip antenna is the most widely used omni-directional antenna
found in the military. The most common example of this type of antenna is
the whip antenna used on vehicles, and the ground plane antenna that is
usually mounted on masts or other structures. The expedient, vertical quarterwave, whip antenna, like the antenna shown in the diagram below, is a single
bare or insulated wire held vertically by a means of support and connected to
the antenna connector on the face of the radio.
Frequency and
Height
The vertical whip is omni-directional, and its efficiency is related to the
transmitting frequency and antenna height. At lower frequencies, it is rather
inefficient, but as the frequency increases so does the efficiency. Antenna
height can be improved by placing the antenna on top of a hill or by fastening
it to a pole or tree to boost the efficiency of this antenna.
Construction
Instructions for constructing this antenna can be found in Appendix A, OmniDirectional Antenna Construction.
MCI Course 2515H
3-41
Study Unit 3, Lesson 4
Field Expedient Ground Plane Antennas
Characteristics
These field expedient antennas operate at frequencies above 20 MHz. They
are either pole supported or tree hung, as shown in the diagram below, and
their radiation pattern is omni-directional. The vertical and ground plane
elements are cut for a quarter wave, the ground plane elements should be at
45-degree angles. Insulators are used to separate vertical elements from the
ground plane elements.
Construction
Instructions for constructing this antenna can be found in Appendix A, Biand Uni-Directional Antenna Construction.
MCI Course 2515H
3-42
Study Unit 3, Lesson 4
Lesson 4 Exercise
Directions
Complete items 1 through 10 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
Through
Item 4
Matching: For items 1 through 4, match the field expedient antenna in
column 1 to the illustration in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Field Expedient Antenna
Illustration
___ 1.
___ 2.
___ 3.
___ 4.
a.
Half-wave dipole
Long wire
Sloping "V"
Vertical quarter wave whip
b.
c.
d.
Continued on next page
MCI Course 2515H
3-43
Study Unit 3, Lesson 4
Lesson 4 Exercise, Continued
Item 5
Through
Item 7
Matching: For items 5 through 7, match the field expedient antenna in
column 1 to the illustration in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Field Expedient Antenna
Illustration
___ 5. Two-element yagi
___ 6. Half-rhombic
___ 7. Ground plane
a.
b.
c.
Item 8
Optimum performance can be achieved with the long wire antenna by
a.
b.
c.
d.
terminating one leg of the antenna with a 500-ohm resistor.
placing a reflecting element behind the radiating element.
mounting the antenna in a vertical or diagonal position.
directing a major lobe toward the intended receiver.
Continued on next page
MCI Course 2515H
3-44
Study Unit 3, Lesson 4
Lesson 4 Exercise, Continued
Item 9
Terminating a half-rhombic antenna with a resistor causes it to become
a.
b.
c.
d.
Item 10
What length should the vertical and ground plane elements be cut for an
expedient ground plane antenna?
a.
b.
c.
d.
MCI Course 2515H
omni-directional.
uni-directional.
bi-directional.
directional.
One-quarter wave
One radio wave
One-half wave
One full wave
3-45
Study Unit 3, Lesson 4
Lesson 4 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
3
4
5
6
7
8
9
10
Summary
Answer
d
a
b
c
a
b
c
d
b
a
Reference
3-34
3-37
3-40
3-41
3-36
3-39
3-42
3-37
3-39
3-42
In this lesson, you’ve learned about many different types of field expedient
antennas.
In the next lesson, you will learn about the different types of transmission
lines and the role they play in effective communications.
MCI Course 2515H
3-46
Study Unit 3, Lesson 4
LESSON 5
TRANSMISSION LINES
Overview
Introduction
It is important to realize that the feed in line, or transmission line, which
connects the radio to the antenna, is a crucial part of the communication
system. Using an unsuitable transmission line can render the most carefully
constructed antenna inefficient, or damage costly communications equipment.
Content
This lesson discusses the different types of transmission lines and the
phenomenon of standing waves that can plague any transmission line.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Define transmission line.
•
Identify the different types of transmission lines.
•
Define standing waves.
This lesson contains the following topics:
Topic
Overview
Types of Transmission Lines
Standing Waves
Lesson 5 Exercise
CI Course 2515H
3-47
See Page
3-47
3-48
3-52
3-53
Study Unit 3, Lesson 5
Types of Transmission Lines
Definition
A transmission line is a conductor that transfers radio frequency (RF) energy
from the transmitter to the antenna or from the antenna to the receiver. Most
radio systems and preconstructed antennas are fielded with custom
transmission lines, cut to the appropriate length and fitted with any necessary
end connectors.
For the purpose of building field expedient antennas or repairing conventional
antennas, the transmission lines discussed in the following pages can be
purchased by the foot through the Marine Corps supply system as well as
electronic hobbyist stores or web sites.
Balanced and
Unbalanced
Transmission lines fall into two main categories:
•
•
Balanced lines
Unbalanced lines
The terms balanced and unbalanced describe the relationship between the
transmission line conductors and the earth.
Balanced
The balanced line is composed of two identical conductors, usually circular
wires separated by air or an insulating material. The voltages between each
conductor and ground, produced by an RF wave as it moves down a balanced
line, are equal and opposite.
For example, at the moment one of the conductors supports a positive voltage
with respect to ground, the other supports a negative voltage of equal
magnitude. Some balanced transmission lines carry a third conductor;
sometimes in the form of a braided shield which acts as a ground.
Continued on next page
CI Course 2515H
3-48
Study Unit 3, Lesson 5
Types of Transmission Lines, Continued
Unbalanced
Unbalanced lines are usually seen in the form of an open single wire line or
coaxial cable. The unbalanced line can be imagined as just one-half of a
balanced line. Examples of both balanced and unbalanced lines are shown in
the diagram below.
Continued on next page
CI Course 2515H
3-49
Study Unit 3, Lesson 5
Types of Transmission Lines, Continued
Parallel TwoWire
The parallel two-wire line shown below consists of two parallel conductors
separated by insulators or spreaders at various intervals. It is available in two
types: spreader bar and twin lead. The spreader bar type uses ceramic or
polystyrene bars as spacers between the two conductors. The impedance for
this type of line is from 50 to 700 ohms. The twin lead consists of two
conductors that are molded into a low-loss polyethylene plastic. It is
available in impedances ranging from 75 to 300 ohms.
Twisted Pair
The twisted pair transmission line shown in the diagram below consists of
two insulated conductors twisted together. The purpose of twisting the lines
together is to give the line greater strength and to cancel out the effects of
nearby magnetic or electric fields. The impedance of twisted pair line is
generally 70 to 100 ohms. The advantages of this type of line are ease of
construction and accessible material. The disadvantages of using the twisted
pair transmission lines are that some RF loss in transmission line power may
occur and extreme care must be taken when using this type of transmission
line with HF or high-powered equipment.
Continued on next page
CI Course 2515H
3-50
Study Unit 3, Lesson 5
Types of Transmission Lines, Continued
Shielded Pair
The shielded pair transmission line shown below consists of two conductors
separated and surrounded by insulation material. The insulation material is
then covered with a flexible copper braid that acts as a shield. This shield is
then coated with rubber or a similar material to protect it against moisture and
friction. Because of the shield, the line is not effected by nearby electric or
magnetic fields. Shielded pair transmission lines have the benefit of center
conductors that are balanced to ground and uniform capacitance across the
entire length of the line. This balance is due to the grounded shield that
surrounds the conductor with a uniform spacing along the entire length.
Coaxial Cable
The coaxial transmission line shown below consists of two conductors, a
center conductor and an outer shield. The center conductor can be a solid
strand of copper or two or more small strands of copper twisted together. A
polyethylene plastic shell surrounds the center conductor and provides
uniform characteristics throughout the cable. The outer conductor is a
flexible copper braid allowing this cable to carry high frequencies with
minimal RF loss. This ability to carry high frequencies with very low loss or
risk of RF radiation makes the coaxial cable the most widely used cable in
Marine Corps conventional antennas and communications systems. The
advantages of the coaxial cable are that it is waterproof and durable, easy to
work with, safe from shock hazard when constructed properly, and readily
available. The disadvantage of this cable is its high cost.
CI Course 2515H
3-51
Study Unit 3, Lesson 5
Standing Waves
Definition
A standing wave is a motionless wave on an antenna that can cause voltage
and current to be reflected back down the transmission line into the
transmitter. Standing waves result in power loss and poor antenna efficiency.
Impedance
Impedance describes the nature and size of anything that impedes the flow of
current; in the case of antennas and transmission lines, RF waves. Any circuit
that contains capacitance or inductance and operates at some frequency has
impedance. Impedance, like resistance, is expressed in ohms, but cannot be
measured with an ordinary ohmmeter.
Impedance
Mismatch
The impedance of an antenna at the point where the transmission line (also
called a feed line) is attached is called the antenna input impedance. For
maximum efficiency, an antenna must be the proper length for the frequency
at which it operates. Just as important, the characteristic impedance or
impedance of the transmission line and the antenna input impedance must
match. Additionally, the output impedance of the transmitter must match the
impedance of the feed line. If a mismatch occurs anywhere in the antenna
system, standing waves will result.
Standing Wave
Ratio
Most military transmitters provide 50-ohm impedance at the antenna output.
Most expedient half-wave antennas have approximately a 70-ohm impedance.
By matching the transmission line to the transmitter with a 50-ohm line, a 20ohm difference at the antenna results or by matching the transmission line to
the antenna with a 70-ohm line, a 20-ohm difference at the transmitter results.
If you were to transmit in this mismatched state, a standing wave would be
produced. Comparing the amplitude of this standing wave with the output of
the transmitter results in an efficiency rating known as the standing wave ratio
(SWR). By dividing 70 ohms by 50 ohms, you will see that the SWR is 1.4 to
1. For safety reasons and for the good of the equipment, it is recommended
that you not operate a system with a mismatch or SWR greater than 1.5 to 1.
CI Course 2515H
3-52
Study Unit 3, Lesson 5
Lesson 5 Exercise
Directions
Complete items 1 through 9 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1 Through
4
Matching: For items 1 through 4, match the type of transmission line in
column 1 to the illustration in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Type of Transmission Line
Illustration
___ 1.
___ 2.
___ 3.
___ 4.
a.
Shielded pair
Twisted pair
Parallel two-wire
Coaxial cable
b.
c.
d.
Continued on next page
CI Course 2515H
3-53
Study Unit 3, Lesson 5
Lesson 5 Exercise, Continued
Item 5
Define transmission line.
______________________________________________________________
______________________________________________________________
Item 6
What are standing waves?
______________________________________________________________
______________________________________________________________
Item 7
What are the advantages of using twisted pair transmission line?
a.
b.
c.
d.
Item 8
A disadvantage of using twisted pair transmission line is that it is
a.
b.
c.
d.
Item 9
extremely expensive.
dangerous with HF.
dangerous with RF.
not waterproof.
Name one advantage of using a shielded pair transmission line.
a.
b.
c.
d.
CI Course 2515H
Economical and safe with high powered equipment
Ease of construction and accessible material
Waterproof, lightweight, and easy to handle
Carries high frequencies with minimal loss
It has very high impedance.
It has uniform capacitance.
It has no outer shielding.
Ease of construction.
3-54
Study Unit 3, Lesson 5
Lesson 5 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
3
4
5
6
7
8
9
Summary
Answer
b
c
a
d
A conductor that transfers radio
frequency (RF) energy from the
transmitter to the antenna or from the
antenna to the receiver
A motionless wave on an antenna
b
b
b
Reference
3-51
3-50
3-50
3-51
3-48
3-52
3-50
3-50
3-51
In this study unit, you’ve learned about the functions of an antenna. You
learned about antenna polarization, the polarization requirements of various
frequencies, and the conventional field antennas used within the Marine
Corps. You have also learned several types of field expedient antennas and
several types of transmission lines that can be used to feed these antennas.
In the next study unit, you will learn about selecting a suitable
communications site and proper antenna grounding.
CI Course 2515H
3-55
Study Unit 3, Lesson 5
STUDY UNIT 4
SITE SELECTION AND ANTENNA GROUNDING
Overview
Introduction
Two factors play an important role in selecting a communications site:
optimum communications and camouflage. Unfortunately, it is seldom
possible to situate your equipment in a position conducive to good
communication and yet be hidden from enemy view, fire, or direction finding
efforts. From a communications point of view, the ideal location for a radio
antenna is far away from cover on a bare mountaintop or in the middle of a
large field. Obviously, this does mesh with the tactical requirement to be
hidden from the enemy’s view.
Because you cannot always obtain the best locations for your antenna sites,
antenna grounding is also an important factor to consider. Usually the most
frequent cause of a weak signal, especially HF signals, is poor grounding.
You can easily increase your communication distance by properly grounding
the antenna.
WARNING:
Ungrounded high-powered transmitters can damage
equipment or shock, burn, or kill Marines.
Scope
This study unit discusses the technical and tactical requirements crucial to
proper site selection. This study unit also discusses various counter measures
and precautions that can be taken when selecting an antenna site. Lastly, this
study unit introduces you to various types of grounding equipment.
In This Study
Unit
This study unit contains the following lessons:
Topic
Requirements for Site Selection
Electronic Warfare Considerations
Grounds and Counterpoises
MCI Course 2515H
4-1
See Page
4-3
4-11
4-17
Study Unit 4
(This page left intentionally blank.)
MCI Course 2515H
4-2
Study Unit 4
LESSON 1
REQUIREMENTS FOR SITE SELECTION
Overview
Introduction
The choice of an antenna site will depend on the nature of the local
intervening terrain and the tactical situation. Planning should be preceded by
a careful study of terrain maps and whenever possible, by reconnaissance, in
order to obtain detailed information concerning the availability, accessibility,
and feasibility of desirable sites.
Content
This lesson discusses the technical and tactical factors that must be taken into
consideration when selecting a communications site.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Identify the technical factors that influence site selection.
•
Identify the tactical factors that influence site selection.
This lesson contains the following topics:
Topic
Overview
Technical Factors
Tactical Factors
Lesson 1 Exercise
MCI Course 2515H
4-3
See Page
4-3
4-4
4-6
4-8
Study Unit 4, Lesson 1
Technical Factors
Definition
Technical factors that effect communications site selection are factors that
relate to the characteristics of equipment being used and the nature of the
communications mission.
Factors
Technical factors that effect communications site selection include
•
•
•
•
•
•
•
•
•
•
•
Location
Terrain
Ground conditions
Foliage
Manmade obstructions
Bridges
Buildings
Suspended power lines
Roads
Other electrical equipment
Noisy areas
Location
A site must be located in a position that will ensure communication with the
other stations with which it is to operate. To obtain efficient transmission and
reception, the factors listed below should be considered.
Terrain
Hills and mountains between stations normally limit the range of radio sets.
In mountainous or hilly terrain, positions relatively high on the slopes should
be selected. Locations at the base of a cliff or in a deep ravine or valley
should be avoided. For operation at frequencies above 30 MHz, a location
that will give line-of-sight communication should be selected whenever
possible.
Ground
Conditions
Dry ground has resistance, therefore, limits the range of the radio set. If
possible, the station should be located near moist ground, which has much
less resistance. Water, and in particular salt water, will greatly increase the
distances that can be covered and also provides a better earth ground for the
equipment.
Continued on next page
MCI Course 2515H
4-4
Study Unit 4, Lesson 1
Technical Factors, Continued
Foliage
Trees with heavy foliage absorb radio waves, with leafy trees causing a
greater detriment than evergreens. The antenna should be kept clear of all
foliage and dense brush.
Man-Made
Obstructions
In addition to the natural obstructions listed on the previous page, many manmade obstructions should be avoided when selecting an antenna site. The
most common of these obstructions are listed below.
Bridges
A position in a tunnel or beneath an underpass or steel bridge should be
avoided. Transmission and reception under these conditions are almost
impossible because of high absorption of RF waves.
Buildings
Buildings located in the transmission path, particularly steel and reinforced
concrete structures hinder transmission and reception.
Suspended
Power Lines
All types of pole wire lines, such as telephone and high power lines, should
be avoided when selecting a site for a radio station. Such wire lines absorb
power from radiating antennas located in their vicinity. They also introduce
hum and noise interference in receiving antennas.
Roads
Positions adjacent to heavily traveled roads and highways should be avoided.
In addition to the noise and confusion caused by tanks and trucks, ignition
systems in these vehicles may cause electrical interference.
Other
Electrical
Equipment
Avoid electrical interference from other electrical equipment by avoiding the
following:
Noisy Areas
Radio stations should be located in relatively quiet areas. Copying weak
signals require great concentration by the operator, and his or her attention
should not be diverted by extraneous noises.
MCI Course 2515H
• Other commercial or military communication sites
• Battery charging units
• Generators
4-5
Study Unit 4, Lesson 1
Tactical Factors
Definition
Tactical factors that effect communications site selection are factors that
relate to the military nature of the mission, the threat of enemy attack, and the
proximity of enemy forces.
Factors
Tactical factors that effect communications site selection include
•
•
•
•
•
•
Local command requirements
Cover and concealment
Terrain and camouflage
Remote operation
Local coordination
Final considerations
Local
Command
Requirements
Communication sites should be located some distance from the unit
headquarters or command post that they serve. Thus, long-range enemy
artillery fire, missiles, or aerial bombardment directed at the stations as a
result of enemy direction finding would not strike the command post area.
Cover and
Concealment
The locations selected should provide the best cover and concealment
possible, consistent with good transmission and reception. Perfect cover and
concealment may impair transmission and reception. The amount of
permissible impairment depends on the range required, the power of the
transmitter, the sensitivity of the receiver, the efficiency of the antenna
system, and the nature of the terrain. When a radio is being used to
communicate over a distance that is well under the maximum range, some
sacrifice of communication efficiency can be made to permit better
concealment from enemy observation.
Terrain and
Camouflage
Open crests of hills and mountains must be avoided. A slightly defiladed
position just behind the crest gives better concealment and sometimes
provides better transmission. All permanent and semi-permanent positions
should be properly camouflaged for protection against both aerial and ground
observation. However, the antenna should not touch trees, brush, or
camouflage material.
Continued on next page
MCI Course 2515H
4-6
Study Unit 4, Lesson 1
Tactical Factors, Continued
Remote
Operation
Antennas of all radio sets must extend above the surface of the ground to
permit normal communications. However, most man-packed radio sets have
sufficient cord length to permit operation from cover, while the radio set is
below the surface of the surrounding terrain and the antenna is in the clear.
Some sets can be controlled remotely from distances of 100 feet or more.
Radio sets of this type can be set up in a relatively exposed position while the
operator remains concealed.
Local
Coordination
Contact must be maintained between the communications site and the
message center at all times, either by local messenger or field telephone. The
station should also be readily accessible to the unit commander and his or her
staff.
Final
Considerations
It is almost impossible to select a radio site that will satisfy all technical and
tactical requirements. Therefore, a compromise is usually necessary and the
best site available is selected. It is also a good idea to select both a primary
and an alternate site. Then, if radio communication cannot be established at
the primary location, the set can be moved a short distance to the alternate
position.
MCI Course 2515H
4-7
Study Unit 4, Lesson 1
Lesson 1 Exercise
Directions
Complete items 1 and 2 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
Technical factors that effect communications site selection include
a.
b.
c.
d.
Item 2
Tactical factors that effect communications site selection include
a.
b.
c.
d.
MCI Course 2515H
cover and concealment, remote operation, and camouflage.
buildings, roads, and ground conditions.
bridges, buildings, and remote operations.
local command requirements, ground conditions, and foliage.
cover and concealment, remote operation, and camouflage.
buildings, roads, and ground conditions.
bridges, buildings, and remote operations.
local command requirements, ground conditions, and foliage.
4-8
Study Unit 4, Lesson 1
Lesson 1 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
Summary
Answer
b
a
Reference
4-4
4-6
In this lesson, you’ve learned about technical and tactical factors that are
crucial to selecting a communication site.
In the next lesson, you will learn about electronic warfare and how it effects
the selection of an antenna site.
MCI Course 2515H
4-9
Study Unit 4, Lesson 1
(This page left intentionally blank.)
MCI Course 2515H
4-10
Study Unit 4, Lesson 1
LESSON 2
ELECTRONIC WARFARE CONSIDERATIONS
Overview
Introduction
When operating any kind of radio equipment in a tactical environment, it is
important to remember the radio waves you are transmitting can give away
your position. Our adversaries train and equip directional finding forces with
sophisticated equipment that can pinpoint your location if you do not employ
the proper counter measures.
Content
This lesson discusses electronic warfare (EW) and the counter measures that
can be taken to defeat enemy directional finding and jamming efforts.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
Define antenna masking.
•
Identify one advantage of using directional horizontally polarized
antennas in an EW environment.
This lesson contains the following topics:
Topic
Overview
Antenna Placement
Antenna Selection
Lesson 2 Exercise
MCI Course 2515H
4-11
See Page
4-11
4-12
4-14
4-15
Study Unit 4, Lesson 2
Antenna Placement
Placement
Utilizing the antenna placement methods described below can greatly
improve your chances of defeating enemy radio directional finding (RDF)
efforts.
Antenna
Masking
Antenna masking, like that shown in the diagram below, is the technique of
hiding radio signals behind terrain. It is an inexpensive way to confuse RDF
efforts. VHF radio waves bend; they are reflected by buildings and
mountains and absorbed by trees. When this happens, it is difficult to
determine the original direction from which the wave was transmitted, but the
ability to hear the signal is minimally effected. A radio operator can
advantageously use this principle by attempting to place terrain obstacles
between the transmitter and the forward edge of the battle area (FEBA) while
affording an unblocked path to the intended receivers. Hills, lakes, and dense
forest also provide terrain obstacles. Antenna masking also occurs when
antennas are positioned on the back slopes of hills. A radio operator should
also erect antennas as low as adequate communications permit and, in all
cases, antennas should be camouflaged to blend with terrain.
Continued on next page
MCI Course 2515H
4-12
Study Unit 4, Lesson 2
Antenna Placement, Continued
Antenna
Dispersion
MCI Course 2515H
When numerous antennas are used, it is important to place them some
distance apart from each other so that their cumulative radiation does not
appear to be coming from one large source. Good antenna dispersion also
means planning for alternate locations, using terrain analysis to find antenna
locations that can provide natural masking from the enemy, and employing
the services of agencies such as the Joint Spectrum Center (JSC). As you will
see in Appendix B, JSC can support the Marine communicator in the field by
supplying coverage and propagation predictions that simplify the frequency
and location selection process.
4-13
Study Unit 4, Lesson 2
Antenna Selection
Importance
Choosing the right type of antenna for your mission is as important as
selecting the right antenna location. If you carefully select and employ your
antennas, direction finding will be more difficult and expensive for your
adversaries.
Vertical, OmniDirectional
Antennas
For versatility, the omni-directional, vertically polarized antenna is best. The
flexibility provided by omni-directional antennas is important to the
commander during the attack when it is difficult to maintain correct
orientation for horizontally polarized directional antennas. Additionally,
vertically polarized omni-directional antennas are required for
communications between moving vehicles. Unfortunately, the omnidirectional antenna has one chief disadvantage—danger. Omni-directional
antenna signals travel in a 360-degree radius and usually well across the
FEBA where they are susceptible to interception and RDF.
Horizontal,
Directional
Antennas
Horizontally polarized, directional antennas should be considered for lateral
communications in an EW environment whenever possible for the following
reasons:
MCI Course 2515H
•
The horizontal antenna produces a more stable signal in the presence of
interference (jamming).
•
The horizontal antenna produces a more stable signal when used in or
near dense woods.
•
The horizontal antenna is more readily camouflaged without loss of
signal.
•
Small changes in antenna location do not cause large variations in signal
strength.
•
The horizontal antenna is more difficult to direction find because of
polarization and because its signal can be directed to intended recipients
and away from enemy RDF in many applications.
4-14
Study Unit 4, Lesson 2
Lesson 2 Exercise
Directions
Complete items 1 and 2 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
Define antenna masking.
______________________________________________________________
______________________________________________________________
Item 2
Name one advantage of using horizontal polarization in an EW environment.
______________________________________________________________
______________________________________________________________
MCI Course 2515H
4-15
Study Unit 4, Lesson 2
Lesson 2 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
Answer
1
The technique of hiding radio signals
behind terrain.
2
• The horizontal antenna produces a
more stable signal in the presence of
interference (jamming).
• The horizontal antenna produces a
more stable signal when used in or
near dense woods.
• The horizontal antenna is more
readily camouflaged without loss of
signal.
• Small changes in antenna location do
not cause large variations in signal
strength.
• The horizontal antenna is more
difficult to direction find because of
polarization and because its signal can
be directed to intended recipients and
away from enemy RDF in many
applications.
Summary
Reference
4-12
4-14
In this lesson, you’ve learned about antenna placement and selection
techniques that can be used to minimize RDF threat.
In the next lesson, you will learn about grounding and counterpoises.
MCI Course 2515H
4-16
Study Unit 4, Lesson 2
LESSON 3
GROUNDS AND COUNTERPOISES
Overview
Introduction
When grounded antennas are used, it is important that the ground be as
conductive as possible. This is necessary to reduce ground losses and to
provide the best possible reflecting surface for the radiated energy from the
antenna above.
Content
This lesson discusses the importance of proper grounding and introduces you
to various types of grounding rods, radial grounds, counterpoises, and ground
screens.
Learning
Objectives
At the end of this lesson, you should be able to
In This Lesson
•
State the purpose of grounds
•
Define grounding rods.
•
Define radial grounds.
•
Describe a counterpoise.
•
Describe a ground screen.
This lesson contains the following topics:
Topic
Overview
Grounds
Grounding Rods
Radial Grounds
Counterpoise
Ground Screen
Lesson 3 Exercise
MCI Course 2515H
4-17
See Page
4-17
4-18
4-19
4-20
4-21
4-22
4-23
Study Unit 4, Lesson 3
Grounds
Definition
At low and medium frequencies, the ground normally acts as a sufficiently
good conductor, although care must be taken to make connection to the
ground in such a way as to introduce the least possible amount of resistance in
the ground connection. At higher frequencies, artificial grounds constructed
of large metal surfaces are common.
Types of
Grounds
The ground connection takes many forms, depending on the type of
installation and the loss that can be tolerated. For fixed station installations,
very elaborate ground systems are used. These are frequently arranged over
very large areas so that they operate as part of the reflecting surface in
addition to making the connection to ground itself. In many simple field
installations, the ground connection is made by means of one or more metal
rods driven into the earth.
Soil Conditions
Sometimes when an antenna must be erected over soil having a very low
conductivity, it is advisable to treat the soil directly to reduce its resistance.
In this case, the conductivity can be improved by treating the soil with
substances that are highly conductive when in solution. Some of these
substances, listed in order of preference, are
•
•
•
•
•
Sodium chloride (common salt)
Calcium chloride
Copper sulfate (blue vitriol)
Magnesium sulfate (epsom salt)
Potassium nitrate (saltpeter)
The amount required depends on the type of soil and its moisture content.
When these substances are used, it is important that they do not get into
nearby drinking water supplies.
MCI Course 2515H
4-18
Study Unit 4, Lesson 3
Ground Rods
Description
With a less elaborate ground system, a number of ground rods can be used.
These rods usually are made of galvanized iron, steel, or copper plated steel in
lengths up to 8 feet. One end of the rod is pointed so that it can be driven
easily into the earth. The other end is fitted with some type of clamp, in the
case of longer rods, so that the ground lead can be attached. In the case of
shorter rods, the other end is usually threaded to allow the connection of
additional rods. Some ground rods are supplied with a length of ground lead
already attached.
Placement
Using several ground rods, 6 to 10 feet apart, connected in parallel, can make
a good ground connection. If possible, the rods should be located in a moist
section of ground or in a natural or man-made depression that will collect
moisture. Ground resistance can be reduced considerably by treating the soil
with any of the substances previously mentioned. A trench about a foot deep
is dug around each ground rod and filled with some common rock salt, Epsom
salt, or any of the other materials mentioned. The trench is then flooded with
water, causing the treatment to permeate into the soil. During sustained
operations, be sure to replenish the water as needed.
Installation
It is important that a low resistance connection be made between the ground
wire and the ground rod. The rod should be cleaned thoroughly by scraping
or sanding the point where the connection is to be made, and a clean ground
clamp installed. A ground wire can then be soldered or joined to the clamp.
The joint should be covered with tape to prevent an increase in resistance
caused by oxidation.
Alternate
Grounds
Where more satisfactory arrangements cannot be made, it may be possible to
make ground connections to existing devices that are already grounded.
Metal structures or underground pipe systems (such as water pipes)
commonly are used as ground connections. In an emergency, a suitable
ground connection can be obtained by plunging one or more bayonets into the
earth. Other field expedient ground rods are metal fence posts, steel
reinforcing rods, water pipes, conduit, and metal building frame.
MCI Course 2515H
4-19
Study Unit 4, Lesson 3
Radial Grounds
Definition
MCI Course 2515H
Radial grounds, as shown in the diagram below, consist of a number of bare
conductors arranged radially and connected. The conductors, which may be
from a tenth to a half-wave length or more, are buried a short distance beneath
the surface of the earth. If possible, bare metal plates should be attached to
the wire ends that improve the quality of the ground.
4-20
Study Unit 4, Lesson 3
Counterpoise
Definition
When an actual ground connection cannot be used because of the high
resistance of the soil or a large buried ground system is not practicable, a
counterpoise may replace the usual direct ground connection in which current
actually flows to and from the antenna through the ground itself. The
counterpoise shown in the diagram below consists of a structure made of
wire, which is erected a short distance off the ground and insulated from the
ground. The counterpoise should be at least equal to or preferably larger than
the antenna.
Vertical
Antenna
Applications
When the antenna is mounted vertically, the counterpoise should be made into
a simple geometric pattern such as those shown in the diagram above. Perfect
symmetry is not required, but the counterpoise should extend for equal
distances in all directions from the antenna.
Vehicular
Applications
If some UHF antenna installations are on vehicles, the metal roof of the
vehicle is used as a counterpoise for the antenna.
Special VHF
Applications
Small counterpoises of metal mesh are sometimes used with special VHF
antennas that must be located a considerable distance above the ground. This
counterpoise provides an artificial ground that helps to produce the required
radiation pattern.
MCI Course 2515H
4-21
Study Unit 4, Lesson 3
Ground Screen
Definition
A ground screen consists of a fairly large area of metal mesh or screen that is
laid on the surface of the ground under the antenna. Its purpose is to simulate
the effect of a perfect conducting ground under the antenna.
Advantages
There are two specific advantages that can be gained through use of a ground
screen:
MCI Course 2515H
•
The ground screen reduces ground absorption losses that occur when an
antenna is erected over imperfectly conducting ground.
•
The height of the antenna can be set accurately:
•
The radiation resistance of the antenna can be determined.
•
The radiation patterns of the antenna can be predicted more accurately.
4-22
Study Unit 4, Lesson 3
Lesson 3 Exercise
Directions
Complete items 1 through 5 by performing the action required. Check your
answers against those listed at the end of this lesson.
Item 1
The purpose of grounds is to
a.
b.
c.
d.
Item 2
Which of the following is made of galvanized iron, steel, or copper plated
steel in lengths of up to 8 feet?
a.
b.
c.
d.
Item 3
Ground rod
Counterpoise
Radial ground
Ground screen
Which of the following consist of a number of bare conductors arranged and
buried a short distance beneath the surface of the earth?
a.
b.
c.
d.
Item 4
have resistance as high as possible.
have conductivity as low as possible.
increase ground losses and to provide the best energy from the antenna.
introduce the least possible amount of resistance in the ground connection.
Ground rod
Counterpoise
Radial ground
Ground screen
A structure made of wire that is constructed a short distance off the ground
and insulated from the ground describes a
a.
b.
c.
d.
ground rod.
counterpoise.
radial ground.
ground screen.
Continued on next page
MCI Course 2515H
4-23
Study Unit 4, Lesson 3
Lesson 3 Exercise, Continued
Item 5
A fairly large area of metal mesh that is placed on the ground directly under
the antenna describes a
a.
b.
c.
d.
MCI Course 2515H
ground rod.
counterpoise.
radial ground.
ground screen.
4-24
Study Unit 4, Lesson 3
Lesson 3 Exercise
Solutions
The table below lists the solutions to the exercise items. If you have any
questions about these items, refer to the reference page.
Item Number
1
2
3
4
5
Summary
Answer
d
a
c
b
d
Reference
4-18
4-19
4-20
4-21
4-22
In this study unit, you’ve learned about grounding systems that can be used to
enhance the performance of both field expedient and conventional antennas.
The following appendices will aid you in the construction of field expedient
antennas and assist you in frequency selection.
MCI Course 2515H
4-25
Study Unit 4, Lesson 3
(This page intentionally left blank.)
MCI Course 2515H
4-26
Study Unit 4, Lesson 3
APPENDIX A
FIELD EXPEDIENT ANTENNA CONSTRUCTION
Overview
Introduction
This appendix discusses some field expedient solutions to repairing tactical
whip and ground plane antennas if they become broken or damaged. It covers
seven field expedient antennas that can be used either alone or in conjunction
with conventional tactical antennas.
Scope
This appendix serves as a step-by-step guide to aid you in the repair of
common Marine Corps antennas and the fabrication of field expedient
antennas. This appendix is a professional reference guide designed to
enhance your abilities; this information is not tested in this course.
In This
Appendix
This appendix contains the following topics:
Topic
Overview
Types of Antennas
Omni-Directional Antenna Repair
Omni-Directional Antenna Construction
Bi- and Uni-Directional Antenna Construction
Formulas and Quick Reference Charts
Field Expedient Antenna Supplies
MCI Course 2515H
A-1
See Page
A-1
A-2
A-3
A-8
A-16
A-28
A-31
Appendix A
Types of Antennas
Explanation
When fabricating a field expedient antenna, it is important to know the
location of the distant station(s) you will need to communicate. The direction
and distance of these distant station(s) will determine which type of antenna is
used.
Types
Basically, there are three types of antennas:
Type
Omni-directional
Bi-directional
Uni-directional
Definition
All directions
Any two opposite directions
Any one direction
Note: The frequency hoping functions are not supported with the expedient
antennas.
Examples
MCI Course 2515H
The three types of antennas are identified in the diagrams below:
A-2
Appendix A
Omni-Directional Antenna Repair
Two Types
There are two types of omni-directional antennas:
•
•
The Vertical
Whip
Vertical whip—used on vehicles
• Metallic whip
• Fiberglass whip
Ground plane—mounted on masts or other structures
The vertical whip antenna is the most widely used omni-directional antenna
in the military:
•
Efficiency relates to the transmitting frequency
• Lower frequencies—efficiency is very low
• Higher frequencies—efficiency increases
•
Efficiency interacts with height of antenna
• Place the antenna on top of a hill
• Fasten it to a pole or tree to increase its height above surrounding
structures
Repairs
If your vertical whip antenna is damaged or missing a part, consider the
following quick solutions to your problem:
•
•
Metallic whip repair
Fiberglass whip repair
Continued on next page
MCI Course 2515H
A-3
Appendix A
Omni-Directional Antenna Repair, Continued
Metallic Whip
Broken Into
Two Pieces
If a metallic whip antenna becomes broken into two pieces, a splint is the
quickest repair you can make. To repair this type of break, perform the steps
listed in the table below:
Step
1
2
3
Action
Scrape off the paint 3 to 6 inches from the broken ends.
Obtain about one foot of copper wire or stripped WD-1.
Overlay the cleared ends and wrap them together tightly with
the wire. If possible, solder the connection.
Place a dry stick, pole, or branch on each side of the break and
wrap the splint tightly with WD-1, tape, rope or whatever is
available.
If everything else is working right, you're ready to communicate.
Metallic Whip
Broken Into
Two Pieces
Diagram
The steps to repair a broken metallic whip are identified in the diagram
below:
Continued on next page
MCI Course 2515H
A-4
Appendix A
Omni-Directional Antenna Repair, Continued
Metallic Whip
Antenna Lost
Parts
If your metallic whip antenna is broken and the upper piece is lost, perform
the steps listed in the table below:
Step
1
2
3
4
5
6
Action
Obtain a pole 10 feet long, approximately 9 feet of WD-1 and
some tape.
Scrape off the paint from the top 2 inches of the whip's stub.
Wrap 12 inches of bare wire around the scraped portion of the
stub. Wrap very tightly, pass it over the top of the stub, and
jam it into the hole with a wooden peg and tape if possible.
Tie the 10-foot pole tightly to the antenna base and stub.
Attach the WD-1 along the length of the pole with tape. Total
length of the upright WD-1 and antenna stub should not be
more than 9 feet.
Trim away any extra wire.
You are now ready to communicate. Move slowly because this mast will not
withstand abuse like the original, but will serve you well in an emergency.
Missing Parts
Diagram
The steps to repair a metallic whip due to missing parts are identified in the
diagram below:
Continued on next page
MCI Course 2515H
A-5
Appendix A
Omni-Directional Antenna Repair, Continued
Fiberglass
Whip Broken
Into Two Pieces
If a fiberglass whip antenna breaks into two pieces, you cannot use a splint to
fix it like on metal whips. To repair this type of break, perform the steps
listed in the table below.
Step
1
Action
Obtain a 15-foot length of coaxial cable. To separate the
braided shield from the center conductor, perform the substeps listed below:
•
Strip only the outer rubber cover from 5 feet of the cable.
With a sharp knife, carefully cut through the outer
insulation making sure not to cut into the metal braided
shield.
• Once the insulation is cut evenly all around, slide it off
leaving the braided shield exposed.
• Bend the coax in a loop at the point where the outer
insulation ends. Holding the coax loop in one hand,
carefully separate the metal braided shield from the
insulated center conductor with a nail, pencil, or any other
pointed object. Gradually work the coax away from the
insulated center conductor until enough center conductor is
exposed to grasp firmly.
• Keeping the loop formed, grasp the center conductor and
draw it out of the braided shield.
Continued on next page
MCI Course 2515H
A-6
Appendix A
Omni-Directional Antenna Repair, Continued
Fiberglass
Whip Broken
Into Two
Pieces,
continued
Step
2
3
4
5
Action
Obtain a 10-foot dry pole and lash it to the antenna base.
Tape the center conductor to the top half of the pole.
Tape the braided shield to the bottom half of the pole.
If there's a BNC (twist lock type) connector on the coax, attach
it to the radio. If not, strip the end of the center conductor and
carefully insert it into the radio’s antenna connector. Then
attach the braided shield to a screwhead on the radio case.
Remember that this is only a temporary solution, so replace it the first chance
you get.
Continued on next page
MCI Course 2515H
A-7
Appendix A
Omni-Directional Antenna Construction
Preparation
Before constructing any field expedient antennas, it is important to
understand the proper handling procedures for WD-1, also known as slash or
comm wire.
Attach the
WD-1 to the
Connector
Before attaching the WD-1 to the connector of the radio, perform the steps
listed in the table below:
Step
1
2
Insert the
WD-1 Into a
Connector
Action
Loop the wire around the handle of the radio.
If your feed line is bare wire, secure the wire to the ground
using a stake and insulator to keep the antenna wire from
pulling out of the radio’s antenna connector.
Before inserting the bare WD-1 wire end into a connector on an antenna,
radio, or any other device, perform the steps listed in the table below:
Step
1
Action
Look closely at the bare wire; you will see seven strands. Four
strands are flexible copper and give the WD-1 greater
conductivity. The other three strands are steel and give the
WD-1 its strength.
2
Group the copper strands together and bend them away from
the steel strands at a 45-degree angle.
Keep the steel strands straight; neatly wrap the copper strands
around the steel strands.
Trim the exposed wire off at the point where the copper
wrapping ends.
3
4
You now have a durable wire end that can be inserted into connectors
repeatedly without becoming frayed.
Continued on next page
MCI Course 2515H
A-8
Appendix A
Omni-Directional Antenna Construction, Continued
Quarter-Wave
Vertical
Antenna
To replace a regular quarter-wave whip antenna, perform the steps listed in
the table below:
Step
1
2
3
Action
Using the quick reference chart or the formula for a quarter
wave at the end of this appendix, cut a piece of wire to the
required length.
Attach an insulator to one end of the wire and attach the other
end to the antenna connector on the radio.
Attach a second piece of wire or a piece of rope to the insulator
end and throw the wire/rope over a limb.
Continued on next page
MCI Course 2515H
A-9
Appendix A
Omni-Directional Antenna Construction, Continued
Quarter-Wave
Vertical
Antenna,
continued
Step
4
Action
Pull the antenna up until it is vertical and taut.
The verticals are constructed the same way, but each has a
different means of support. They are all simple and quick to
erect.
If you are using insulated wire, be sure to loop the wire around
the handle of the radio before attaching it to the antenna
connector. If your antenna is made of bare wire, use a stake
and insulator to keep the antenna wire from pulling out the
antenna connector on the radio.
Continued on next page
MCI Course 2515H
A-10
Appendix A
Omni-Directional Antenna Construction, Continued
Tree-Hung
Ground Plane
The tree-hung antenna is a good emergency replacement for the OE254/GRC. This omni-directional, improvised antenna can be used in wooded
areas where a tree limb can be used to suspend the antenna. To construct the
tree-hung antenna, perform the steps listed in the table below:
Step
1
•
Action
Use the quick reference chart or the formula for a quarterwave at the end of this appendix.
•
Cut a piece of wire to the required length.
2
Obtain three slender branches of equal size.
3
Position the three branches to form a triangle and tie the ends
together.
4
Tie one end of each of the three quarter-wave elements to each
corner of the triangle.
Continued on next page
MCI Course 2515H
A-11
Appendix A
Omni-Directional Antenna Construction, Continued
Tree-Hung
Ground Plane,
continued
Step
5
Action
Obtain an insulator and attach the free end of the three elements
to it.
6
Attach the fourth quarter-wave element to the other end of the
insulator.
7
Secure the wire or rope that will be used to suspend the antenna
on the opposite end of the fourth element. Attach another
insulator to this insulator.
Continued on next page
MCI Course 2515H
A-12
Appendix A
Omni-Directional Antenna Construction, Continued
Tree-Hung
Ground Plane,
continued
Step
8
9
Action
Attach the transmission line to the antenna by attaching one end
to the three ground plane elements and the other end to the
vertical element.
Raise the antenna and tie it off. Then attach the transmission
line to the antenna connector on the radio.
Continued on next page
MCI Course 2515H
A-13
Appendix A
Omni-Directional Antenna Construction, Continued
Pole Supported
Ground Plane
The pole supported ground plane antenna is employed in the same manner as
its tree-hung counterpart and can be used in areas where there are no trees to
use as supports. To construct a pole supported ground plane, perform the
steps listed in the table below:
Step
1
Action
Obtain a large pole.
2
Compute and cut four wires for a quarter wave.
3
Attach one quarter-wave element (vertical element) to the pole
(the exact location of wire on the pole will depend on antenna
length).
Continued on next page
MCI Course 2515H
A-14
Appendix A
Omni-Directional Antenna Construction, Continued
Pole Supported
Ground Plane,
continued
Step
4
MCI Course 2515H
Action
Attach the other three quarter-wave elements (ground plane
elements) to the pole. Make sure that they are insulated from the
vertical element.
5
Attach insulators to each of the ground plane elements and
attach another wire to the opposite end of each insulator.
6
7
Raise pole and tie down the three ground plane elements.
Connect the transmission line to the vertical and ground plane
elements and to the antenna connector on the radio.
A-15
Appendix A
Bi- and Uni-Directional Antenna Construction
Half-Wave
Dipole
The half-wave dipole, also known as doublet antenna, is a highly effective bidirectional antenna. It is normally used in the HF range, but can also be used
effectively with radios that operate within the VHF range. To construct the
half-wave dipole antenna, you will need the following items:
•
•
•
Two supports (trees or poles)
Three insulators
A length of wire (both for the antenna and halyards). Rope can also be
used for the halyard.
To build this effective antenna, perform the steps listed in the table below:
Step
1
Action
Cut the wire to your operating frequency. Use the quick
reference chart or formulas at the end of this appendix.
2
Determine your direction of transmission, keep in mind that this
antenna is bi-directional.
3
Cut the wire in half, placing an insulator on each wire end as
well as the center.
Continued on next page
MCI Course 2515H
A-16
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Half-Wave
Dipole,
continued
Step
4
5
Action
Locate and/or erect the two supports. Be certain they are 3 or 4
feet farther apart than the antenna's actual length and broadside
to the direction of communications.
Attach your transmission line to both sides of the center
insulator. Make sure that it is long enough to hang straight to
the ground and then to your radio's position.
6
Tie ropes or wires to the two end insulators. Then use whatever
method is easiest, hang the antenna up between the supports,
keeping it as taut as possible.
7
Connect one end of your transmission line to the antenna and the
antenna connector on the radio.
Continued on next page
MCI Course 2515H
A-17
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Two-Element
Yagi
As seen in the diagram below, this configuration consists of a dipole modified
by simply adding a reflecting element (a single wire) one quarter-wave length
behind the dipole. This reflecting element will help increase the gain and
make the antenna more directional. To construct this antenna, perform the
steps listed in the table below:
Step
1
Action
Construct a half-wave dipole.
2
3
Obtain two supports, either poles or trees.
Cut reflecting element. Use the quick reference chart or
formulas at the end of this appendix.
4
Attach the reflecting element to the supports and erect the
reflecting element one quarter wavelength behind the dipole
antenna. Make sure out-station is forward of the antenna and
reflecting elements.
Continued on next page
MCI Course 2515H
A-18
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Long Wire
Antenna
If you need more distance and directivity than your whip antenna will give
you, try making a long wire antenna. The overall length of the antenna must
be between three to seven wavelengths of the operating frequency depending
on the operating area and amount of construction material on hand. With this
antenna, you will find that you can communicate over longer distances in
either one or two directions. This antenna is bi-directional for high power
VHF and HF. For low power VHF, this antenna is uni-directional when
terminated with a 500 to 600-ohm, 2-watt carbon resistor. To construct the
long wire antenna, perform the steps listed in the table below:
Step
1
Action
Determine the direction of the station you need to reach and line
up your antenna. Plan all your work in that direction.
2
Cut antenna wire to the desired length. Use the quick reference
chart or formulas at the end of this appendix.
3
Select two antenna supports, paying close attention to your
operating area. If you are operating in a forested area, trees may
be used as supports. If operating in a desert environment, tent or
PO-2 poles may be your only choice, so use whatever is
available. Keep in mind the higher off the ground you can get
your antenna, the better it will perform.
Continued on next page
MCI Course 2515H
A-19
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Long Wire
Antenna,
continued
Step
4
Action
Attach the antenna wire to the two supports.
5
Attach an insulator to each end of the antenna wire.
6
Connect tie down wires outside the insulators on each end of the
antenna wire.
Continued on next page
MCI Course 2515H
A-20
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Long Wire
Antenna,
continued
Step
7
8
Action
Raise and tie down the antenna.
Connect transmission line to the antenna and radio set.
Connect resistor to the far end of antenna, if your antenna is to
be uni-directional.
Continued on next page
MCI Course 2515H
A-21
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Sloping “V”
Antenna
The sloping "V" antenna consists of two long wires arranged to form a V
shape, which slopes downwards the ground. It is bi-directional to unidirectional and primarily produces sky waves. To construct the sloping “V”
antenna, perform the steps listed in the table below:
Step
1
Action
Determine the direction of the station you need to reach and line
up your antenna. Plan all your work in that direction.
2
Cut wire for the antenna legs. Leg length is not as critical with
this antenna, but should be at least two wavelengths long.
Antenna wire should be 10 to 16 gauge copper clad wire.
3
Connect insulators to each end of the antenna legs. Add tie
down wires to the opposite ends of each insulator.
Continued on next page
MCI Course 2515H
A-22
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Sloping “V”
Antenna,
continued
Step
4
5
Action
Select a tree or pole to serve as a mast for the antenna.
Connect antenna legs to mast. Using the table below, select the
apex angle depending upon antenna leg length in wavelengths.
Antenna Length
(wavelengths)
1
2
3
4
6
7
Optimum Apex
Angle (degrees)
90
70
58
50
Antenna Length
(wavelengths)
6
8
9
10
Optimum Apex
Angle (degrees)
40
35
34
33
Extend the antenna legs out and stake them down to metal
stakes.
Attach a balanced transmission line to the antenna legs and the
radio set.
Continued on next page
MCI Course 2515H
A-23
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Vertical
Half-Rhombic
The half-rhombic antenna is a terminated vertical antenna. An unbalanced
transmission line, along with a ground or counterpoise increases this
antenna’s distance and directivity. To construct a vertical half-rhombic
antenna, perform the steps listed in the table below:
Step
1
Action
Determine the direction of the distant station and line up your
antenna. Plan all your work in that direction.
2
Cut the antenna wire to length, ensuring that each leg of the
antenna is at least one wavelength long. At 30 MHz, the leg
should be 1 ½wavelengths; at 70 MHz, it should be 3 ½
wavelengths.
3
Connect an insulator to each end of the antenna wire. Add tie
down wires to each insulator.
Select a middle support, such as a tree, pole, or a rope suspended
between two poles or existing structures. The support should be
preferably 30 feet or higher, 20 feet at a minimum.
4
Continued on next page
MCI Course 2515H
A-24
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Vertical
Half-Rhombic,
continued
Step
5
Action
Select one element and run it out in the direction of the distant
station. Stake this element down with a metal stake.
6
Connect antenna wire to the support and raise antenna. If you
are using a rope as your middle support, drape your antenna wire
over the rope.
7
Extend the other end of the antenna wire until it is tight and
stake it down using another metal stake.
Continued on next page
MCI Course 2515H
A-25
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Vertical
Half-Rhombic,
continued
Step
8
Action
Measure and cut another piece of wire to be used as a
counterpoise. This piece of wire should be long enough to span
the distance between the two insulators.
9
Attach one end of the counterpoise between the ground stake
and antenna insulators, then to the other end of the antenna, keep
it a foot off the ground. Make sure the counterpoise is connected
to the support material between the ground stake and antenna
insulator, not to the antenna wire.
10
Attach a transmission line to the antenna and to the radio.
Continued on next page
MCI Course 2515H
A-26
Appendix A
Bi- and Uni-Directional Antenna Construction, Continued
Vertical
Half-Rhombic,
continued
Step
11
MCI Course 2515H
Action
To make this antenna more directional, connect a 500-ohm,
2-watt carbon resistor across the insulators at the end farthest
from the intended receiver.
A-27
Appendix A
Formulas and Quick Reference Charts
Formulas
A quick reference chart is listed in the table below:
To Figure
A Quarter
Wavelength
Antenna in Feet
Action
Divide 234 (constant) by your operating frequency
in MHz.
A Half Wavelength
Antenna in Feet
Example: 234 divided by 44.8 = 5.22 feet or 5' 3"
Divide 468 (constant) by your operating frequency
in MHz.
A Full Wavelength
Antenna in Feet
Example: 468 divided by 56 = 8.36 feet or 8' 4"
Divide 936 (constant) by your operating frequency
in MHz.
A Multiple
Wavelength
Antenna in Feet
Example: 936 divided by 45=20.8 feet or 20' 10"
Divide 936 (constant) by operating frequency in
MHz, then multiply the resultant by the desired
antenna wavelength.
Convert Feet to
Meters
Convert Meters to
Feet
Example: 936 divided by 45 = 20.8, for an antenna
4 wavelengths long, 20.8 multiplied by 4 = 83.2 or
83' 3"
Multiply by .3048 (constant).
Example: 110 feet times .3048 = 33.5 meters
Multiply by 3.28 (constant).
Example: 100 meters times 3.28 = 328
Continued on next page
MCI Course 2515H
A-28
Appendix A
Formulas and Quick Reference Charts, Continued
High
Frequency (HF)
Use the table below to determine the length of the antenna for high
frequencies:
Operating
Frequency in MHz
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
High Frequency (HF)
Quarter Wave
Half Wave
117'
78'
58' 6"
46' 9"
39'
33' 5"
29' 3"
26'
23' 5"
21' 3"
19' 6"
18'
16' 9"
15' 7"
14' 7"
13' 9"
13'
234'
156'
117'
93' 7"
78'
66' 10"
58' 6"
52'
46' 10"
42' 6"
39'
36'
33' 5"
31' 2"
29' 2"
27' 6"
26'
Full Wave
468'
312'
234'
187' 4"
156'
133' 8"
117'
104'
93' 8'
85'
78'
72'
66' 10"
62' 4"
58' 4"
55'
52'
Continued on next page
MCI Course 2515H
A-29
Appendix A
Formulas and Quick Reference Charts, Continued
Very High
Frequency
(VHF)
Use the table below to determine the length of the antenna for very high
frequencies:
Operating
Frequency in MHz
30
33
35
37
40
43
45
48
50
55
57
60
65
68
70
75
80
MCI Course 2515H
Very High Frequency (VHF)
Quarter Wave
Half Wave
7' 10"
7' 1"
6' 9"
6' 4"
5' 10"
5' 5"
5' 3"
4' 10"
4' 9"
4' 3"
4' 1"
3' 11"
3' 7"
3' 5"
3' 4"
3' 1"
3'
A-30
15' 7"
14' 2"
13' 5"
12' 7"
11' 8"
10' 1"
10' 5"
9' 8"
9' 5"
8' 6"
8' 2"
7' 10"
7' 2"
6' 10"
6' 7"
6' 2"
5' 11"
Full Wave
31' 2"
28' 4"
26' 10"
25' 2"
23' 4"
21' 8"
20' 10"
19' 4"
18' 10"
17'
16' 4"
15' 8"
14' 4"
13' 8"
13' 2"
12' 4"
11' 10"
Appendix A
Field Expedient Antenna Supplies
Field Tool Kit
If you are going to be constructing field expedient antennas on a regular basis,
it is a good idea to build a field expedient tool kit. The tools and equipment
you will need can be scrounged or purchased through the Marine Corps
supply system or local electronic hobby stores. Keep the kit in a standard
issue canvas bag or ammunition can for safekeeping and easy deployment.
The kit should be inventoried and cleaned and lubricated on the same
schedule as most issued toolkits.
Contents
Your toolkit should contain the items listed in the table below:
Quantity
1 each
1 each
2 each
1 each
2 each
1 each
1 each
1 each
3 sheets
1 each
1 each
2 rolls
30 feet
4 feet
15 feet
4 each
4 each
1 each
1 each
1 roll
1 box
1 box
1 box
1 box
1 box
1 box
1 box
1 each
100 feet
6 each
4 each
6 each
1 each
Description
Screwdriver with assorted tips
Multi-tool, such as Leatherman®
6" Crescent® wrench
Miniature "AA" size flashlight
Spare "AA" batteries
Spare flashlight bulb
Small button-type compass
Small wire brush
Assorted sandpaper
Small all purpose brush
Pencil eraser
Electrical tape
Antenna wire
Insulated 18 gauge wire
Coaxial line (RG-58)
BNC connector
BNC to Banana type adapter
Hand drill
Small butane-powered soldering torch
Solder
Assorted solder lugs
Assorted (crimp-type) wire ends
Assorted metal screws
Assorted bolts
Assorted nuts
Assorted washers
Nails
Hammer
Nylon twine or "550" cord
Insulators
Hose clamps
Alligator clips
Broadband balun
Continued on next page
MCI Course 2515H
A-31
Appendix A
Field Expedient Antenna Supplies, Continued
Emergency
Supplies
If you find yourself in a situation where you need to construct a field
expedient antenna and do not have the proper supplies, you can improvise by
making the following substitutions:
Original Issue
Antenna wire
Antenna mast
Antenna guy ropes
Guy stakes
Insulators
MCI Course 2515H
Field Issue
Barbed wire, electrical cord
Trees, sticks, telephone poles
Cloth belts, slings, boot laces
Rocks, vehicles, trees
MRE spoons, buttons, rags
A-32
Appendix A
APPENDIX B
JOINT SPECTRUM CENTER (JSC)
Overview
Introduction
The effectiveness of the command and control, and the ability of the
communications system to respond to a rapidly changing tactical situation
will determine the degree of success on the modern battlefield. Effective
communications systems require accurate and timely communications
electronics engineering analysis support for operational and combat units. To
meet this demand, the Joint Chiefs of Staff has established the Joint Spectrum
Center (JSC). Based in Annapolis, Maryland, JSC has served to ensure the
DOD’s effective use of the electromagnetic spectrum in support of national
security and military objectives since 1960. JSC provides operational support
by assisting Marine Corps units in identifying the anticipated physical and
electronic environment and then providing analysis support assessing the
effect of the environment on the unit's ability to accomplish its mission.
Scope
This appendix describes the various analytical capabilities and the input data
required for Marine Corps communications electronics engineering and
electro-magnetic compatibility support through JSC.
Note: Appendix B is professional reference material designed to enhance
your abilities only; this information is not tested in this course.
In This
Appendix
This appendix contains the following topics:
Topic
Overview
Point-to-Point Multichannel Predictions
Received Signal Level (RSL) Coverage Overlays
Line-of-Sight (LOS) Coverage Overlays
High Frequency (HF) Sky Wave Propagation Predictions
High Frequency (HF) Ground Wave Propagation Predictions
Three-Dimensional Terrain Plots
Terrain Horizon Plots
How to Contact the JSC
MCI Course 2515H
B-1
See Page
B-1
B-2
B-4
B-7
B-10
B-11
B-12
B-13
B-14
Appendix B
Point-to-Point Multichannel Predictions
Description
The point-to-point multichannel circuit reliability analyses predict short-term
reliabilities for wideband multichannel circuits. Reliability is predicted by
determining the terrain-dependent path loss, received signal level, and
estimated fade margin. Data provided in the prediction includes antenna
horizon angle, true and magnetic azimuths, path distance, reliability
percentages, and propagation modes.
Terrain Profile
For point-to-point reliability analyses, a profile of the terrain between two
points can also be beneficial. The diagram below shows such a terrain
profile.
Continued on next page
MCI Course 2515H
B-2
Appendix B
Point-to-Point Multichannel Predictions, Continued
Required
Information
The following information is required for point-to-point multichannel
reliability predictions:
•
•
•
•
•
•
•
•
MCI Course 2515H
Transmitter and receiver site locations, latitude/longitude, DDMMSS
Equipment nomenclature and model number
Antenna gain (dBi), if known
Type of antennas, transmitter and receiver
Required delivery date
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-3
Appendix B
Received Signal Level (RSL) Coverage Overlays
Description
Radio RSL coverage overlays are used to depict the approximate signal levels
around a transmitter site taking into account such circuit parameters as
transmitter power, transmit and receive antenna gains, and terrain topographic
elevations data. This type of analysis is used to predict the area of reliable
communications for tactical equipment and to determine the susceptibility of
friendly equipment to enemy intercept/jamming. The RSL coverage overlays
are normally provided at a map scale of 1:250,000, but may be varied to meet
the user’s needs. The coverage predictions can represent one transmitter,
multiple transmitters, or the combined/composite coverage of several
transmitters. The overlays can represent ground-to-ground, air-to-ground,
and ground-to-air coverage.
Single Site
Coverage
Overlay
The diagram below is an example of a received signal level coverage overlay
for a single site. The tic marks on the contour lines point to the area of lesser
signal strength.
Continued on next page
MCI Course 2515H
B-4
Appendix B
Received Signal Level (RSL) Coverage Overlays, Continued
Multiple Site
Coverage
Overlay
The diagram below is an example of a received signal level coverage overlay
for multiple sites. The tic marks on the contour lines point to the area of
lesser signal strength.
Continued on next page
MCI Course 2515H
B-5
Appendix B
Received Signal Level (RSL) Coverage Overlays, Continued
Required
Information
The following information is required for RSL coverage overlays:
•
•
•
•
•
•
•
•
•
MCI Course 2515H
Transmitter site location, latitude/longitude, DDMMSS
Transmitter output power
Transmitter and receiver antenna type
Antennas gain, if known
Antenna height above ground
Equipment type and model number
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-6
Appendix B
Line-of-Sight (LOS) Coverage Overlays
Description
Light-of-sight (LOS) coverage overlays depict LOS around radio and radar
sites. This analysis is especially useful for choosing relay/retransmission sites
for tactical radios and microwave terminal locations, and for positioning other
LOS communication equipment. Additionally, radar LOS coverage overlays
enable easy assessment of site suitability with respect to the detection of
incoming targets.
LOS Overlay
The diagram below is an example of a radio LOS coverage overlay for a
tactical transmitter. The tic marks on the contour lines point to the areas that
are within the transmitter’s line-of-sight.
Continued on next page
MCI Course 2515H
B-7
Appendix B
Line-of-Sight (LOS) Coverage Overlays, Continued
Radar Overlay
The diagram below is an example of a LOS coverage overlay for radar
equipment. The coverage contours shown depict the radar target acquisition
distance for targets at various altitudes. Target altitudes may be specified
above mean sea level (MSL) or above ground level (AGL). In this example,
target altitudes of 250 to 8,000 feet above MSL are specified.
Continued on next page
MCI Course 2515H
B-8
Appendix B
Line-of-Sight (LOS) Coverage Overlays, Continued
Required
Information
The following information is required for LOS coverage overlays:
•
•
•
•
•
•
•
•
•
MCI Course 2515H
Transmitter site location, latitude/longitude, DDMMSS
Transmitter antenna height above ground
Coverage radius
Target altitudes (radar LOS only)
Receiver antenna height above ground (radio LOS only)
Required delivery date
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-9
Appendix B
High Frequency (HF) Sky Wave Propagation Predictions
Description
High frequency (HF) sky wave propagation predictions describe the usable
frequencies and the predicted circuit reliability between a transmitter and
receiver site. The most common formats available for JSC HF predictions are
•
•
•
Method 28
Method 31
Method 34
Method 28
Method 28 provides predictions for maximum usable frequency (MUF),
frequency of optimum transmission (FOT), and lowest usable frequency
(LUF) for HF sky wave path between a transmitter and receiver site for a 24hour period for a specific month.
Method 31
Method 31 provides the frequency of optimum transmission (FOT), take-off
angle (ANG), and the predicted reliability (REL) (in percent) of selected
frequencies between a transmitter and receiver site for a 24-hour period for a
specific month.
Method 34
Method 34 shows the FOT, ANG, and REL between a transmitter site and
multiple receiver sites for a 24-hour period for a specific month.
Required
Information
The following information is required for HF propagation predictions:
•
•
•
•
•
•
•
•
•
•
•
MCI Course 2515H
Transmitter site location, latitude/longitude, DDMMSS
Receiver site location(s)/latitude(s)/longitude(s), DDMMSS
Transmitter output power
Type of antenna(s)
Emission designator(s)
Man-made noise at the receiver site (industrial, residential, rural, remote)
Day, month, and year of the start and end of transmission
Required delivery date
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-10
Appendix B
High Frequency (HF) Ground Wave Propagation Predictions
Description
HF ground wave propagation predictions provide the predicted range over
which a ground wave signal is expected to be reliably received during a
24-hour period. These calculations are based on the path distance, transmitter
power, emission type, antenna heights, and ground conductivity along the
communications path. Effective month of the predictions, transmitter power,
type antennas, frequency values, path loss, and distances are depicted in the
output. The calculations do not consider the effects of atmospheric
phenomena, detailed topography, or foliage. Additionally, the path can be
incremented when transmission is over land and water. Incrementing allows
the analyst to define the variations in ground constants for the different types
of soil.
Required
Information
The following information is required for HF propagation predictions:
•
•
•
•
•
•
•
•
•
•
•
MCI Course 2515H
Transmitter site location, latitude/longitude, DDMMSS
Desired radius around transmitter location (KM or SM)
Transmitter output power
Type of antenna(s)
Emission designator(s)
Man-made noise at the receiver site (industrial, residential, rural, remote)
Day, month, and year of the start and end of transmission
Required delivery date
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-11
Appendix B
Three-Dimensional Terrain Plots
Description
Three-dimensional terrain plots display the topographical data for a specific
area in the form of a three-dimensional graph. These plots are useful for a
quick identification of possible relay/retransmission sites and for map studies
of exercise or contingency areas. The plots are produced in several colors,
one for each elevation threshold and can be plotted on 36” by 36” paper. The
diagram below provides an example of a three-dimensional terrain plot.
Required
Information
The following information is required for a three-dimensional terrain plot:
•
•
•
•
•
MCI Course 2515H
Latitude/longitude, DDMMSS of the four corners of the area of interest
Required delivery date
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-12
Appendix B
Terrain Horizon Plots
Description
The terrain horizon plot illustrates the terrain contour information around a
specified site location. These plots can be used to graphically represent the
radio or visual horizon around a site. To meet their requirements, the users
may vary the scan angel (azimuth) and horizon angle (elevation). The
diagram below provides an example of a terrain horizon plot.
Required
Information
The following information is required for a terrain horizon plot:
•
•
•
•
•
•
•
•
•
•
•
MCI Course 2515H
Site location latitude/longitude, DDMMSS
Antenna height
Initial scan angle (degree)
End scan angle (degree)
Lowest horizon angle (degree)
Highest horizon angle (degree)
Horizon distance (statute miles)
Required delivery date
Organization and mailing address
Phone numbers (voice and fax)
Point of contact
B-13
Appendix B
How to Contact the JSC
Contact
Information
Contact the Joint Spectrum Center, J3 for support. Points of contact are as
follows:
•
•
•
•
•
•
•
•
More
Information
MCI Course 2515H
DSN 281-2814/2328/9815, normal duty hours
COMM 401-293-2814/2328/9815, normal duty hours
STU III & Secure FAX DSN 281-2452, normal duty hours
FAX DSN 281-3763/COMM 410-293-3763, 24 hours
After normal duty hours: 410-991-3143, PIN 419-8623 (pager)
Message address: JSC ANNAPOLIS MD//J3//
E-mail: [email protected]
SIPRNET: [email protected]
For more information concerning the mission of the JSC, visit their website at
http://www.jsc.mil/
B-14
Appendix B
ANTENNA CONSTRUCTION AND PROPAGATION OF
RADIO WAVES
REVIEW LESSON EXAMINATION
Review Lesson
Introduction
The purpose of the review lesson is to prepare you for your final examination.
We recommend that you try to complete your review lesson without referring
to the text, but for those items (questions) you are unsure of, restudy the text.
When you have finished your review lesson and are satisfied with your
responses, check your responses against the answers provided at the end of
this review lesson examination.
Directions
Select the ONE answer that BEST completes the statement or answers the
item. For multiple-choice items circle your response. For matching items
place the letter of your response in the space provided.
Item 1
What part of a radio set is used for sending radio signals?
a.
b.
c.
d.
Item 2
Demodulator
Transmitter
Receiver
Amplifier
What component of a radio set extracts the desired electro-magnetic waves
from the air, amplifying them and removing the intelligence in the
demodulation process?
a.
b.
c.
d.
Antenna
Receiver
Transmitter
Power converter
Continued on next page
MCI Course 2515H
R-1
Review Lesson Examination
Review Lesson, Continued
Item 3
What device is used for transmitting and receiving radio waves?
a.
b.
c.
d.
Item 4
What provides operating voltage to a radio set?
a.
b.
c.
d.
Item 5
sky
ground
magnetic
radio
The number of complete cycles that occurs in one second determines the
a.
b.
c.
d.
Item 7
Power supply
Direct current
Alternating current
Carrier wave
Electro-magnetic energy radiated from an antenna is known as
______________ waves.
a.
b.
c.
d.
Item 6
Receiver
Transmitter
Antenna
Demodulator
frequency of a radio wave.
amount of energy available in a power supply.
type of power supply needed to operate a radio set.
speed at which electro-magnetic energy travels through space.
What is the formula for finding the length (in meters) of a radio wave when
the frequency is known?
a.
b.
c.
d.
3,000 divided by the frequency
30,000 divided by the frequency
300,000 divided by the frequency
300,000,000 divided by the frequency
Continued on next page
MCI Course 2515H
R-2
Review Lesson Examination
Review Lesson, Continued
Item 8
What type of wave acts as a medium for the transmission of information
signals?
a.
b.
c.
d.
Item 9
The process that varies or modifies either the frequency or amplitude of the
carrier waveform is known as the
a.
b.
c.
d.
Item 10
critical frequency.
transmission.
modulation.
carrier wave converter.
What type of modulation varies the RF power output of a transmitter?
a.
b.
c.
d.
Item 11
Carrier
Frequency
Transmission
Received
FM
FSK
SSB
AM
What is the process called that varies the frequency of a carrier wave in
proportion to the amplitude of the modulating signal?
a.
b.
c.
d.
FM
FSK
AM
SSB
Continued on next page
MCI Course 2515H
R-3
Review Lesson Examination
Review Lesson, Continued
Item 12
Digital modulation is accomplished by shifting the ___________ of the
carrier wave.
a.
b.
c.
d.
Item 13
A gaseous mass that envelops the earth describes the
a.
b.
c.
d.
Item 14
Troposphere, ionosphere, and stratosphere
Stratosphere, troposphere, and ionosphere
Troposphere, stratosphere, and ionosphere
Ionosphere, troposphere, and stratosphere
Which region of the ionosphere has little effect in bending the paths of high
frequency radio waves?
a.
b.
c.
d.
Item 16
autmosphere.
source of ionization.
atmosphere.
regions in outer space.
Name the three regions of the atmosphere in order of their relative heights.
a.
b.
c.
d.
Item 15
data
amplitude
frequency
phase
F1
F2
E
D
Which region of the ionosphere is ionized at all hours of day and night?
a.
b.
c.
d.
D
E
F
G
Continued on next page
MCI Course 2515H
R-4
Review Lesson Examination
Review Lesson, Continued
Item 17
The chief factor that controls long distance communication is the _________
of the ionized layer.
a.
b.
c.
d.
Item 18
Which two layers of the ionosphere are the most highly ionized?
a.
b.
c.
d.
Item 19
the highest frequency of transmission.
modes of transmission.
critical frequency.
interference frequency.
A ground wave is a radio wave that travels
a.
b.
c.
d.
Item 21
D and E
D and F
E and F
D and F2
The highest frequency at which waves sent vertically upward are reflected
directly back to earth defines
a.
b.
c.
d.
Item 20
location
density
size
color
skyward.
skyward and near the earth's surface.
near the skip zone.
near the earth's surface.
The direct, ground-reflected, and surface waves are all components of the
______________ wave.
a.
b.
c.
d.
sky
single hop
tropospheric
ground
Continued on next page
MCI Course 2515H
R-5
Review Lesson Examination
Review Lesson, Continued
Item 22
Ground wave propagation is extremely useful for communication at
a.
b.
c.
d.
Item 23
What type of radio wave depends on the ionosphere to provide signal paths
between transmitter and receiver?
a.
b.
c.
d.
Item 24
Sky
Ground
Direct
Ground reflected
An area bounded by the outer edge of the usable ground wave propagation
and the point nearest the antenna at which the sky wave returns to earth is
known as the
a.
b.
c.
d.
Item 25
any frequency.
low frequencies.
high frequencies.
super-high frequencies.
skip area.
skip zone.
unusable zone.
skip distance.
The frequencies that return to earth from a fixed angle of departure are known
as the MUF. The MUF used in predicting the operating frequencies refers to
the
a. maximum transmission distance possible for a given operating frequency.
b. minimum transmission distance possible for a given operating frequency.
c. lowest frequency that will provide communication over a specified
distance at a given time.
d. highest frequency that will provide communication over a specified
distance at a given time.
Continued on next page
MCI Course 2515H
R-6
Review Lesson Examination
Review Lesson, Continued
Item 26
Waves of frequency that are transmitted above the _____ will pass through
the ionosphere and escape into space.
a.
b.
c.
d.
Item 27
The lowest limiting frequency for satisfactory sky wave communication for a
radio circuit at a particular time is known as the
a.
b.
c.
d.
Item 28
noise.
reflection.
fading.
interference.
The four types of fading are interference, polarization,
a.
b.
c.
d.
Item 30
LUF.
LOF.
LTF.
LHF.
The periodic increase and decrease of received radio strength is called
a.
b.
c.
d.
Item 29
MUF
FOT
LUF
UMF
absorption, and switch.
antenna, and skip.
absorption, and skip.
reflection, and skip.
What type(s) of radio wave propagation are useful at the medium frequency
band?
a.
b.
c.
d.
Sky only
Sky and reflected
Ground only
Sky and ground
Continued on next page
MCI Course 2515H
R-7
Review Lesson Examination
Review Lesson, Continued
Item 31
In the high frequency band, what are the two types of wave propagation
called?
a.
b.
c.
d.
Item 32
Which of the ground wave components provides the best communications
path when operating in the very-high-frequency band?
a.
b.
c.
d.
Item 33
Ground-reflected
Surface
Direct
Critical
The direct wave component of the ground wave is the only reliable
propagation path available when transmitting in the _____ frequency band.
a.
b.
c.
d.
Item 34
Direct and sky
Reflected and direct
Reflected and ground
Sky and ground
HF
ELF
ULF
UHF
A device that converts the output power of the transmitter into an electromagnetic field for radiation into space is called
a.
b.
c.
d.
transmitting antenna.
power converter.
RF amplifier.
AF amplifier.
Continued on next page
MCI Course 2515H
R-8
Review Lesson Examination
Review Lesson, Continued
Item 35
If a transmitter is supplying power to an antenna, the fluctuating energy sets
up two fields. Which of these two fields remain at a short distance from the
antenna and beyond?
a.
b.
c.
d.
Item 36
The radiation field is composed of two components. They are the electric and
______________ components.
a.
b.
c.
d.
Item 37
induction
magnetic
electron
oscillation
What field is formed from the electric and magnetic components of a radiated
wave?
a.
b.
c.
d.
Item 38
Radiation
Inductive
Magnetic
Electric
Electro-inductive
Electro-magnetic
Magnetic-induction
Electro-motive
The purpose of a receiving antenna is to
a.
b.
c.
d.
radiate energy into space.
vary the frequency of a radio wave.
send received signals to the modulator.
operate as a signal source for the receiver.
Continued on next page
MCI Course 2515H
R-9
Review Lesson Examination
Review Lesson, Continued
Item 39
Polarization of a radiated wave is determined by the direction of the lines of
force making up the __________ field.
a.
b.
c.
d.
Item 40
What are the two types of antenna polarization?
a.
b.
c.
d.
Item 41
Vertical and omni-directional
Vertical and horizontal
Horizontal and directional
Azimuthal and vertical
What kind of antenna polarization should you use when working with low
and medium frequencies?
a.
b.
c.
d.
Item 42
magnetic
induction
electric
radiation
Induction
Horizontal
Electrical
Vertical
Why is it better to horizontally polarize antennas at high frequencies?
a.
b.
c.
d.
They can be made to radiate effectively at high angles.
They are omni-directional.
Vertically radiated waves cannot be refracted from the ionosphere.
Vertically polarized antennas have inherent directional properties.
Continued on next page
MCI Course 2515H
R-10
Review Lesson Examination
Review Lesson, Continued
Item 43
At the very-high and ultra-high frequency bands, which type(s) of antenna
polarization should be used?
a.
b.
c.
d.
Item 44
The AS-2259/GR makes use of short-range sky wave propagation to
communicate over distances ranging from ________ miles.
a.
b.
c.
d.
Item 45
0 to 150
0 to 200
0 to 250
0 to 300
What is the maximum input power of the OE-254/GRC?
a.
b.
c.
d.
Item 46
Vertical polarization only
Horizontal polarization only
Neither vertical nor horizontal
Either vertical or horizontal
300 watts
350 watts
400 watts
3,500 watts
The balun of the OE-254/GRC is responsible for
a.
b.
c.
d.
adjusting the height of the antenna.
securing the radiating elements to the mast.
allowing the operator to adjust the impedance.
matching the impedance of the antenna to the input.
Continued on next page
MCI Course 2515H
R-11
Review Lesson Examination
Review Lesson, Continued
Item 47
Aligning the antenna to the outstation and adding or subtracting the wave
angle can direct the major lobe of the ________ antenna toward the intended
receiver.
a.
b.
c.
d.
Item 48
A half-rhombic antenna when terminated with a resistor becomes
a.
b.
c.
d.
Item 49
uni-directional.
omni-directional.
bi-directional.
directional.
When making a field expedient ground plane antenna, at what length (in
wave) should the vertical and ground plane elements be cut?
a.
b.
c.
d.
Item 50
half-wave dipole
long wire
quarter-wave whip
ground plane
One-quarter wave
One-half wave
Three-quarter wave
One full wave
A conductor that transfers radio frequency energy from the transmitter to the
antenna is called a __________ line.
a.
b.
c.
d.
repeater
carrier
transmission
pulse
Continued on next page
MCI Course 2515H
R-12
Review Lesson Examination
Review Lesson, Continued
Item 51
Ease of construction is just one advantage to using the _______________
transmission line.
a.
b.
c.
d.
Item 52
High cost is one disadvantage to using the ________________ transmission
line.
a.
b.
c.
d.
Item 53
Ease of construction
Readily accessible material
Low cost of material
The conductors are balanced to ground
Standing waves result in
a.
b.
c.
d.
Item 55
coaxial
continuous pair
twisted pair
shielded pair
What is one advantage of using the shielded pair transmission line?
a.
b.
c.
d.
Item 54
shielded pair
parallel two-wire
continuous pair
twisted pair
a fire hazard in the area below the antenna.
a power loss and poor antenna efficiency.
improved reception and greater power output.
a perfect antenna and transmission line match.
Antenna masking is the technique of
a.
b.
c.
d.
causing antenna dispersion.
using decoy antennas.
using remote control radios.
hiding radio signals behind terrain.
Continued on next page
MCI Course 2515H
R-13
Review Lesson Examination
Review Lesson, Continued
Item 56
One advantage of using horizontal polarization in an EW environment is that it
a.
b.
c.
d.
Item 57
The purpose of grounds is to
a.
b.
c.
d.
Item 58
introduce the least possible amount of resistance in the ground connection.
have resistance as high as possible.
have conductivity as low as possible.
increase ground losses and to provide the best energy from the antenna.
Which type of grounding device is made from galvanized iron or steel and
pointed at one end?
a.
b.
c.
d.
Item 59
cannot be seen from the sky.
causes ease of construction in an open area.
has no radiation to be detected by the enemy.
has a more stable signal in or near dense woods.
Radial ground
Ground screen
Grounding rod
Counterpoise
A grounding system consisting of a number of interconnected bare conductors
arranged radially and buried a short distance under ground is known as a
a.
b.
c.
d.
radial ground.
counterpoise.
grounding rod.
ground screen.
Continued on next page
MCI Course 2515H
R-14
Review Lesson Examination
Review Lesson, Continued
Item 60
A structure made from wire that is erected a short distance off the ground and
insulated from the ground describes a
a.
b.
c.
d.
Item 61
Which grounding system reduces ground absorption losses that occur when
an antenna is erected over imperfectly conducting ground?
a.
b.
c.
d.
Item 62
Through
Item 64
ground rod.
counterpoise.
ground screen.
radial ground.
Ground rod
Counter screen
Ground screen
Radial ground
Matching: For items 62 through 64, match the atmospheric layer in column 1
to its description in column 2. Place your responses in the spaces provided.
Column 1
Column 2
Atmospheric Layer
Description
___ 62. Troposphere
___ 63. Ionosphere
___ 64. Stratosphere
a. The region of the atmosphere that
extends from the surface of the
earth to a height of about 6.8
miles
b. The region of the earth’s
atmosphere composed of several
distinct layers
c. The region of the earth’s
atmosphere where the
temperature remains nearly
constant
Continued on next page
MCI Course 2515H
R-15
Review Lesson Examination
Review Lesson, Continued
Item 65
Through
Item 68
Matching: For items 65 through 68, match the polarization benefit in column
1 to the type of polarization in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Polarization Benefit
Type of Polarization
___ 65. Useful in minimizing
a. Vertical
interference from certain
b. Horizontal
directions
___ 66. Useful when communicating
with moving vehicles
___ 67. Is somewhat less effected by
aircraft flying over the
transmission path
___ 68. Suffers lower losses when
located near dense forests
Item 69
Through
Item 73
Matching: For items 69 through 73, match the antenna characteristics in
column 1 to the antenna system in column 2. Place your responses in the
spaces provided.
Column 1
Column 2
Antenna Characteristics
Antenna System
___ 69. Operates in the VHF range, a. AS-2259/GR
b. OE-254/GRC
between 30 and 88 MHz
___ 70. A omni-directional,
biconical antenna
___ 71. Utilizes radiating elements
that double as guy lines
___ 72. Operates in the HF range,
between 2 and 12 MHz
___ 73. Radiating elements are steel
tubes that screw into a
central balun
Continued on next page
MCI Course 2515H
R-16
Review Lesson Examination
Review Lesson, Continued
Item 74
Through
Item 80
Matching: For items 74 through 77, match the field expedient antenna in
column 1 to the illustration in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Field Expedient Antenna
Illustration
___ 74.
___ 75.
___ 76.
___ 77.
a.
Half-wave dipole
Long wire
Sloping "V"
Vertical quarter wave whip
b.
c.
d.
Continued on next page
MCI Course 2515H
R-17
Review Lesson Examination
Review Lesson, Continued
Item 78
Through
Item 80
Matching: For items 78 through 80, match the field expedient antenna in
column 1 to the illustration in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Field Expedient Antenna
Illustration
___ 78. Two-element
___ 79. Half-rhombic
___ 80. Ground plane
a.
b.
c.
Continued on next page
MCI Course 2515H
R-18
Review Lesson Examination
Review Lesson, Continued
Item 81
Through
Item 84
Matching: For items 81 through 84, match the type of transmission line in
column 1 to the illustration in column 2. Place your responses in the spaces
provided.
Column 1
Column 2
Type of Transmission Line
Illustration
___ 81.
___ 82.
___ 83.
___ 84.
a.
Shielded pair
Twisted pair
Parallel two wire
Coaxial cable
b.
c.
d.
Continued on next page
MCI Course 2515H
R-19
Review Lesson Examination
Review Lesson, Continued
Item 85
Through
Item 89
Matching: For items 85 through 89, match the factor for antenna site
selection in column 1 to the type of category in column 2. Place your
responses in the spaces provided.
Column 1
Column 2
Factor
Category
___ 85.
___ 86.
___ 87.
___ 88.
___ 89.
MCI Course 2515H
Local command requirements
Location
Manmade obstructions
Cover and concealment
Remote operations
R-20
a. Technical
b. Tactical
Review Lesson Examination
Review Lesson Solutions
Answers
The table below lists the answers to the review lesson examination items. If
you have questions about these items, refer to the reference page.
Item Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Answer
b
b
c
a
d
a
d
a
c
d
a
d
c
c
d
c
b
c
c
d
d
b
a
b
d
a
a
c
c
d
d
c
d
Reference
1-5
1-5
1-5
1-5
1-6
1-7
1-8
1-14
1-14
1-15
1-16
1-18
2-5
2-5
2-8
2-8
2-9
2-9
2-9
2-16
2-16
2-38
2-17
2-19
2-24
2-24
2-26
2-30
2-31
2-38
2-38
2-38
2-38
Continued on next page
MCI Course 2515H
R-21
Review Lesson Examination
Review Lesson Solutions, Continued
Item Number
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
Answer
a
a
b
b
d
c
b
d
a
d
d
b
d
b
a
a
c
d
a
d
b
d
d
a
c
a
b
c
a
b
c
b
a
Reference
3-4
3-4
3-4
3-4
3-5
3-12
3-12
3-14
3-14
3-14
3-23
3-27
3-27
3-37
3-39
3-42
3-48
3-50
3-51
3-51
3-52
4-12
4-14
4-18
4-19
4-20
4-21
4-22
2-6
2-6
2-6
3-16
3-15
Continued on next page
MCI Course 2515H
R-22
Review Lesson Examination
Review Lesson Solutions, Continued
Item Number
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
MCI Course 2515H
Answer
a
b
b
b
a
a
b
d
a
b
c
a
b
c
b
c
a
d
b
a
a
b
b
R-23
Reference
3-15
3-16
3-25
3-25
3-22
3-23
3-25
3-34
3-37
3-40
3-41
3-36
3-39
3-42
3-51
3-50
3-50
3-51
4-6
4-4
4-5
4-6
4-7
Review Lesson Examination
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement