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Precision Ham Radio Measurements
U S E R G U I D E A N D A P P L I C AT I O N N O T E
FOR THE DPM6000 SWR/POWER
METER
Roger M. Stenbock W1RMS
8/1/2016
This user’s guide covers the operation, maintenance and calibration of the preciseRF
DPM6000 digital SWR/Power meter and also incorporates the application note covering power
measurements of RF to microwave signals in the communications industry and ham radio
environment. Accurate power measurements of RF/microwave signals require an in-depth
understanding of the amplitude-varying nature of the signals under test.
This guide and application note explains how you can measure RF Power ranging from low
HF signals to the microwave GHz range. We’ll review the fundamentals of power
measurements, explain SWR, return loss, reflection coefficient, line losses, PEP/average power
and operation of the new PreciseRF DPM6000 power meter.
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TA B L E O F C O N T E N T S
TERMS AND CONDITIONS!
5
NOTICE!
5
WARRANTY!
5
CERTIFICATION !
5
WARRANTY SERVICE!
5
TECHNOLOGY LICENSES!
6
GENERAL SAFETY INFORMATION !
6
ORGANIZATION!
7
TERMS AND CONDITIONS!
7
ORGANIZATION!
7
INTRODUCTION!
7
USER INTERFACE!
7
MAKING POWER MEASUREMENTS!
7
MEASUREMENT CONSIDERATIONS!
7
METROLOGY PRACTICES!
7
FIELD CALIBRATION!
7
FACTORY CALIBRATION!
7
RF POWER TERMS!
7
SPECIFICATIONS!
7
POWER MEASUREMENTS FUNDAMENTALS!
7
INTRODUCTION!
8
FEATURES!
8
DUAL CHANNELS!
9
STABILITY!
9
BRIGHT OLED DISPLAY!
9
DUAL CHANNEL ARCHITECTURE!
10
HIGH ACCURACY AND RESOLUTION!
10
BUILT-IN POWER REFERENCE!
10
SENSOR/COUPLER CHOICE!
10
THE USER INTERFACE!
12
THE DPM6000 FRONT PANEL!
12
CONTROL KEYS!
12
THE DPM6000 REAR PANEL!
13
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HF-VHF PAGES!
13
SET PAGES.!
14
FREQ PAGES!
15
UHF PAGES!
15
START-UP PAGE!
16
MAKING POWER MEASUREMENTS!
17
MAKING MEASUREMENTS WITH AN IN-LINE COUPLER!
17
MICROWAVE SENSOR MWSD6 MEASUREMENTS!
19
CALIBRATING THE MICROWAVE SENSOR!
20
MAKING FREQUENCY MEASUREMENTS!
21
MEASURE THE FREQ COUNTER INPUT FREQUENCY!
21
MEASURE THE RF INPUT (FORWARD) FREQUENCY!
21
MEASUREMENT CONSIDERATIONS!
22
MEASUREMENT UNCERTAINTY!
22
CUMULATIVE EFFECT OF UNCERTAINTY ON MEASUREMENTS.!
23
MAXIMIZING MEASUREMENT CERTAINTY!
24
TEMPERATURE EFFECTS!
24
METROLOGY PRACTICES!
26
SPECTRUM ANALYZER!
26
OSCILLOSCOPE!
26
ANALOG POWER METER!
26
FIELD CALIBRATION!
28
CALIBRATION OF FORWARD AND REFLECTED GAIN!
28
CALIBRATING THE DPM6000 WITH THE PWR REFERENCE!
28
CALIBRATING THE FORWARD GAIN!
29
CALIBRATING THE REFLECTED GAIN!
29
CALIBRATING THE DPM6000 WITH COUPLER(S)!
30
CALIBRATE THE MICROWAVE SENSOR !
31
FACTORY CALIBRATION!
32
EQUIPMENT REQUIREMENTS!
32
ADJUST THE 10,000,000HZ CLOCK DUTY CYCLE!
33
ADJUST THE 10,000,000HZ CLOCK FREQUENCY!
34
CALIBRATE THE 2.50VDC REFERENCE VOLTAGE!
34
CALIBRATE THE KEYPAD!
35
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CALIBRATE THE AD8307 LOGARITHMIC AMPLIFIERS!
36
ADJUST THE FORWARD AND REFLECTED INTERCEPTS!
36
CALIBRATE THE ANALOG TO DIGITAL CONVERTER SLOPE!
37
CALIBRATE THE POWER REFERENCE!
39
UPDATING THE FIRMWARE!
40
REPLACING THE MICRO-CONTROLLER!
40
RF POWER TERMS!
41
VSWR !
41
RETURN LOSS!
42
REFLECTION COEFFICIENT!
43
MISMATCH LOSS!
43
DBM!
45
TRANSMISSION LINE!
49
SPECIFICATIONS !
52
POWER MEASUREMENTS FUNDAMENTALS!
53
RF POWER SENSORS TYPES!
53
THERMISTOR SENSOR !
53
THERMOCOUPLE SENSOR!
53
DIODE SENSOR!
54
DPM6000 POWER METER COUPLERS!
55
RF POWER !
55
POWER OVER TIME!
56
WHAT IS ELECTRIC POWER!
56
PEP POWER VERSUS CW POWER!
56
PEAK POWER!
57
AVERAGE POWER!
57
DPM6000 POWER METER CALCULATIONS!
58
PEP POWER!
59
DIGITAL POWER METERS!
60
LABORATORY GRADE POWER METERS!
60
POWER METER FOR HAM RADIO !
61
ANALOG RF POWER METERS!
62
DPM6000 POWER METER DEVELOPMENT TEAM!
63
ABOUT THE AUTHOR!
63
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I. T E R M S A N D C O N D I T I O N S
2. NOTICE
The information contained in this document is subject to change without
notice. PreciseRF makes no warranty of any kind with regard to this material,
including but not limited to, the implied warranties of merchantability and
fitness for a particular purpose. PreciseRF shall not be liable for errors
contained herein or for incidental or consequential damages in connection
with the furnishing, performance, or use of this material.
3. WARRANTY
The material contained in this document is provided “as is,” and is subject to
being changed, without notice, in future editions. Further, to the maximum
extent permitted by applicable law, PreciseRF disclaims all warranties, either
expressed or implied with regard to this document and any information
contained herein, including but not limited to the implied warranties of
merchantability and fitness for a particular purpose. Duration and conditions
of warranty for this product may be superseded when the product is
integrated into (becomes a part of) other PreciseRF products. During the
warranty period, PreciseRF will, at its option, either repair or replace
products which prove to be defective. The warranty period begins on the
date of delivery or on the date of installation if installed by PreciseRF.
4. CERTIFICATION
PreciseRF certifies that this product met its published specifications at the
time of shipment. PreciseRF further certifies that its calibration was
accomplished with instruments which are traceable to the United States
National Institute of Standards and Technology (NIST).
5. WARRANTY SERVICE
For warranty service or repair, this product must be returned to a service
facility designated by PreciseRF. For products returned to PreciseRF for
warranty service, the Buyer shall pre-pay shipping charges and PreciseRF
shall pay shipping charges to return the product to the Buyer. However, the
Buyer shall pay all shipping charges, duties, and taxes for products returned
to PreciseRF from another country. To the extent allowed by local law, the
remedies provided herein are the Buyer’s sole and exclusive remedies.
PreciseRF shall not be liable for any direct, indirect, special, incidental, or
consequential damages (including lost profit or data), whether based on
warranty, contract, tort, or any other legal theory.
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6. TECHNOLOGY LICENSES
The hardware and/or software described in this document are furnished
under a license and may be used or copied only in accordance with the
terms of such license. All rights are reserved. Reproduction, adaptation, or
translation without prior written permission is prohibited, except as allowed
under the copyright laws.
7. GENERAL SAFETY INFORMATION
1) Do not operate the instrument in an explosive atmosphere or in the
presence of flammable gasses or fumes. For products containing fuses,
do not use repaired fuses or short-circuited fuse holders. For continued
protection against fire, replace the line fuse(s) only with fuse(s) of the
same voltage and current rating and type.
2) Do not perform procedures involving cover or shield removal unless you
are qualified to do so. Operating personnel must not remove the meter
covers or shields. Procedures involving the removal of covers and
shields are for use by service-trained personnel only.
3) Do not service or adjust alone. Under certain conditions, dangerous
voltages may exist even with the instrument switched off. To avoid
electrical shock, service personnel must not attempt internal service or
adjustment unless another person, capable of rendering first aid and
resuscitation, is present.
4) Do not operate damaged instrument. Whenever it is possible that the
safety protection features built into this instrument have been impaired,
either through physical damage, excessive moisture, or any other
reason, REMOVE POWER and do not use the instrument until safe
operation can be verified by service-trained personnel. If necessary,
return the instrument to PreciseRF for service and repair to ensure the
safety features are maintained.
5) Do not substitute parts or modify the instrument. Because of the danger
of introducing additional hazards, do not install substitute parts or
perform any unauthorized modification to the instrument. Return the
instrument to the PreciseRF organization.
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II. O R G A N I Z A T I O N
I. TERMS AND CONDITIONS
This chapter provides an overview of RF power measurements. It introduces
the various power sensors and provides context to power measurements.
II. ORGANIZATION
This chapter provides an overview of the user interface. It covers the various
front panel controls and syntax.
III. INTRODUCTION
This chapter provides the information on the DPM6000 general operation,
initial inspection, performance tests, and front panel display of the PreciseRf
DPM6000 power meter. It covers how to calibrate the sensors.
IV. USER INTERFACE
This chapter provides an overview of the user interface. It covers the various
front panel controls and syntax.
V. MAKING POWER MEASUREMENTS
This chapter describes the built-in self-tests, error messages, and general
maintenance, adjustments, operation, troubleshooting and repair of the
PreciseRF DPM6000 power meter and sensors.
VI. MEASUREMENT CONSIDERATIONS
This chapter covers the methods used to get the best measurement
accuracy.
VII.METROLOGY PRACTICES
This section covers metrology practices, measurement uncertainty and RF
measurement instruments.
VIII.FIELD CALIBRATION
This chapter covers how to calibrate the DPM6000 by the user.
IX. FACTORY CALIBRATION
Covers in detail how to calibrate the unit to factory specifications.
X. RF POWER TERMS
Defines the terms used in power measurements.
XI. SPECIFICATIONS
This chapter lists the specifications and characteristics of the DPM6000.
XII.POWER MEASUREMENTS FUNDAMENTALS
Discusses some of the fundamentals and theory in measuring power.
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III. I N T R O D U C T I O N
The DPM6000 Digital SWR/Power Meter provides the high accuracy
measurement capability demanded by ham radio operators and engineers
alike, at a price that’s affordable. It features simplicity of operation required
for bench top use. It provides very accurate measurements from -60 dBm to
+20 dBm (sensor dependent) and has a rapid display update rate for tuning
applications. The bright easy-to-read OLED display shows both forward and
reflected power.
1. FEATURES
✦ High 80 dB dynamic range
✦ High power measurements (2.0 KW)
✦ 500 MHz forward and reflected power
✦ 6 GHz range with external sensor
✦ 0 dBm 50 MHz power reference
✦ Forward power frequency display
✦ TCXO Front panel counter input
✦ Precision 100MHz counter
✦ Accurate 10 MHz frequency reference
✦ Internal & external counter clock
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2. DUAL CHANNELS
The DPM6000 is a dual channel power meter employing high dynamic range
log amps using AD8307 logarithmic amplifiers. They are complete 500 MHz
monolithic demodulating logarithmic amplifiers based on the progressive
compression (successive detection) technique, providing a dynamic range
of 92 dB to ±3 dB law-conformance and 88 dB to a tight ±1 dB error bound
at all frequencies up to 100 MHz.
3. STABILITY
The AD8307 exhibits excellent supply insensitivity and temperature stability
of the scaling parameters. The unique combination of small size, low power
consumption, high accuracy and stability, very high dynamic range, and a
frequency range encompassing audio through HF to UHF makes this
product useful in numerous applications requiring the reduction of a signal
to its decibel equivalent.
4. BRIGHT OLED DISPLAY
the DP6000 is ideal for bench and/or
use in the field. While admittedly
more expensive than LCD displays,
the DPM6000 uses a 20x2 OLED display to provide excellent readability and
contrast in challenging conditions not possible with low cost back-lit LCD
displays. The OLED display, in addition to long life, also uses less power
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and does not suffer from temperature and time degradation of vacuum
florescent displays.
5. DUAL CHANNEL ARCHITECTURE
The dual channel architecture is ideal for simultaneous measurement of
absolute forward power and reflected power. This allows measurement of
VSWR, return loss, reflection coefficient, mismatch loss and measurements
in both conventional watts and dBm format.
6. HIGH ACCURACY AND RESOLUTION
The 0.2 dBm accuracy and high resolution provides for low measurement
uncertainty resulting in a high degree of confidence required for laboratory
and ham radio power measurements.
7. BUILT-IN POWER REFERENCE
Accuracy is a key specification. The DP6000
has a built-in precisionn calibrated power
reference; 32 MHz and power of 0 dBm (1mW)
which was selected to match the needs of ham
radio operators. Use the Power Reference to
quickly calibrate the DPM6000 to ensure you
are making an accurate measurement.
8. SENSOR/COUPLER CHOICE
The DPM6000 uses PreciseRF in-line directional couplers and square law
diode sensors. Depending on the coupler, power measurements of -60 dBm
(.001 uW) to +64 dBm (2500 W) can be measured up to 500 MHz. With the
square law diode sensors, and depending on the sensor selected, and
options installed in DPM6000, power measurements can be made from
-30dBm to +20dBm and from 100 kHz to 20 GHz.
The selection for the FORWARD and REFLECTED inputs are designed for inline directional couplers and or RF samplers. They can measure power from
1 MHz up to 500 MHz over an 80 dB range. The selection takes into account
the attenuation of each coupler:
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can be made from -30dBm to +20 dBm and from 100 kHz to 20 GHz.
The selection for the Forward (F) and Reflected (R) inputs are designed for in-line
directional
samplers.
canOmeasure
from
p
r e c i couplers
s e R and
F or
D RF
P M
6 0 0 They
0 P
W E Rpower
M E
T 1E MHz
R up to 500
MHz over an 80 dB range. The selection takes into account the attenuation of each coupler:
Sensor
Attenuation
Direct Forward / Reflected Input
0 dB
RF Sampler HFS-1.5
forward power
30 dB
DDS-1 dual directional
coupler
forward & reflected
30 dB
DDC-2KW High power
dual directional coupler
forward & reflected
45 dB
MWSD6
Microwave Sensor
standard DPM6000
0 dB
MWSD6
Microwave Sensor
Opt 10 - DPM6000
0 dB
Power Range
- 60 dBm to 17 dBm
Bandwidth
0.001 uW to 63 mW
1 KHz to
500 MHz.
- 30 dBm to 47 dBm
1-100 MHz
0.001 uW to 50 W
- 30 dBm to 47 dBm
1-100 MHz
0.001 uW to 50 W
-15 dBm to 62 dBm
1.8- 54MHz
31 uW to 1584 W
-20 dBm to + 17 dBm
1MHz- 6 GHz
10 uW to 63 mW
-30 dBm to + 17 dBm
1MHz- 6 GHz
1 uW to 63 mW
Table 1.1 Available Sensor/Coupler Option
DPM6000 POWER METER
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IV. T H E U S E R I N T E R F A C E
The user interface was designed for easy operation and to minimize key
strokes. It uses industry standard nomenclature and syntax. All operation is
controlled by a 16 bit microprocessor. Important settings are stored in nonvolatile memory allowing operation with the last configuration used at power
down.
Figure 2.1 Front Panel
1. THE DPM6000 FRONT PANEL
It is arranged in a logical pattern. A high contrast, bright and daylight
readable, OLED 20 by 2 line display is used. The four main functions, HFVHF, UHF, FREQ and SET are controlled by four push buttons. The SET (up)
and (down) keys are used only for setting the calibration values. The ENTER
key is used to enter data and make SET selections.
2. CONTROL KEYS
With exception of the counter reference clock selection (controlled by a back
panel switch) all functions are controlled by push buttons. Once an option is
selected, pressing the ENTER key cycles through the available sub-choices.
Once a sub-choice has been selected, press any option key to return to
normal operation.
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3. THE DPM6000 REAR PANEL
The rear panel provides for the REFLECTED, and FORWARD input, the EXT
10 MHz CLOCK IN and INT 10 MHz CLOCK OUT, the CLOCK IN-EXT switch
and the 8-15 VDC POWER CONNECTOR. The RF Loop allows connection to
the Front panel input connector. The normal position for the CLOCK SWITCH
is INT (internal).
Figure 2.2 The DPM6000 Rear Panel
4. HF-VHF PAGES
There are six (6) HF-VHF measurement choices. They are:
Page
Comments
Power and SWR (This is the default
page at power on.)
FORWARD power in watts and dBm
and REFLECTED power in watts and
dBm
FORWARD PEP and AVG power
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F (Forward) power in Watts, R
(Reflected) power in Watts, SWR, RL
(Return loss) dB
Displays the MLdB (Mismatch loss) in
dB and RC (p) (Reflection Coefficient)
POWER LOSS %,
R (Reflected) Watts and dBm
5. SET PAGES.
There are seven (7) SET pages with accompanying selection choices.
Page
Additional choices Comments
Power supply
None
voltage at power
input jack.
Barograph full
scale. Exceeding
full scale only
pegs the bargraph and causes
no damage.
As the SWR
exceeds the preset limits, the
SWR alarm lights
a front panel LED
and sounds an
audible alarm.
Holds the highest
power sample
detected for a
specific time
period. Use 5
seconds to catch
SSB voice peaks.
Allows selection of
three coupling
coefficients 0dB,
-30dB and -45dB.
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Allows for
calibration of the
UHF Microwave
sensor.
Allows for
calibration of both
forward (shown)
and reflected gain.
6. FREQ PAGES
Page
Comments
COUNTER INPUT - Max 100 MHz
frequency in Hz eight (8) digit display 2
Hz resolution. This input is located on the
front panel labeled COUNTER.
RF INPUT (FWD) - Max 100 MHz
frequency in Hz eight (8) digit display 2
Hz resolution. Given a strong CW signal,
displays the frequency at the forward
input.
Table 2.4 FREQ Pages
7. UHF PAGES
Page
Comments
Displays power from the microwave
sensor in Watts and dBm. Pressing the
INPUT button again cycles function to
the calibrate sensor option.
Allows for calibration of the microwave
sensor. Connect the microwave sensor
to POWER REF output. Recommend a
45 minute warmup prior to calibration.
Using the up and down keys, adjust the
display for 0.00 dBm. Press ENTER to
return to the microwave sensor display.
Table 2.3 Input Pages
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8. START-UP PAGE
Page
Comments
On screen start up, displays firmware
version. V1-072014 means Version 1
compiled July 20, 2014.
Table 2.5 Start-Up Pages
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!U s e r ’ s
G u i d e
P O W E R
-
M E T E R
A p p l i c a t i o n
V. M A K I N G P O W E R M E A S U R E M E N T S
N o t e
III. Making Power Measurements
Refer
to panel
the DPM6000
front panel
control
layout discussed
To
Refer to The DPM6000
front
control layout
discussed
previously.
To make previously.
a
make a measurement you must select a sensor/coupler type. There are two
measurement you must select a sensor/coupler type. There are two types: the square law
types: the square law microwave sensor (MW) available from the front panel
microwave sensor (MW)jack
available
from
front
labeled
MSor
and
an directional
in-line power
labeled
MSthe
and
an panel
in-linejack
power
coupler
dual
coupler with
thecoupler
inputs with
at the
rear
panel.
coupler or dual directional
the
inputs
at the rear panel.
CAUTION: DO NOT EXCEED THE MAXIMUM
COUPLER INPUT POWER LIMITS.
1. Making a power measurement with an In-Line Coupler
1. MAKING MEASUREMENTS WITH AN IN-LINE COUPLER
You can make measurements
either the using either the Forward or Reflected inputs
You can makeusing
measurements
Forward or Reflected
inputson
located
on panel,
the rear
located
the rear
orpanel,
by
an in-line
coupler. has
The three
or by using an in-lineusing
coupler.
The DPM6000
DPM6000 has three pre-set coupler
pre-set coupler selections. You must select a coupler
selections. You must select a
choice. Measurements
usingchoice.
a coupler
or a sampler
coupler
Measurements
using a
coupler
or a sampler
are inare in-line measurements.
They
measure
the forward
measurements.
measure
or reflected power inline
a transmission
line. They
Generally,
the
the forward or reflected power in a
transmission line is terminated
in aline.
load. This load can
transmission
be an antenna, fixed termination or an attenuator,
Figure 3.1 DDC-2KW Coupler
Generally, the transmission line is
typically 50 Ω to 75 Ω,
depending
on
the
application.
terminated in a load. This load can
be an antenna, fixed termination or
(a) Select the coupler you intend to use from one of
an attenuator, typically 50 Ω to 75 Ω,
the three choices. Press the SET button repeatedly until one of the SELECT
depending on the application. Select
COUPLER pages appears.
the coupler you intend to use from
one of the three choices.
Coupler Choice
Attenuation
Power Range
-60 dBm to + 17 dBm
0 dB
(.001uW - 50 mW)
-35 dBm to + 47 dBm
30 dB
(.32uW - 50 W)
-20 dBm to + 62 dBm
45 dB
(10uW - 1584 W)
NOTE: WHEN USING A SAMPLER SUCH AS THE HFS-1.5 TO MEASURE
FORWARD POWER USE THE 30 dB ATTENUATION SELECTION.
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Coupler Choice
P O W E R
M E T E R
Attenuati Power Range
on
0 dB
-60 dBm to + 17 dBm (.001uW 50 mW).
30 dB
-35 dBm to + 47 dBm (.32uW 50 W).
45 dB
-20 dBm to + 62 dBm (10uW 1584 W).
NOTE: WHEN USING A SAMPLER SUCH AS THE HFS-1.5 TO
MEASURE FORWARD POWER USE THE 30 dB ATTENUATION
!U s e r SELECTION.
’ s G u i d e - A p p l i c a t i o n N o t e
Table 3.1 Coupler Choices
PROCEDURE
he ENTER key to cycle through
the available choices. When you are
1)HF-VHF
Select the
coupler
you to
intend
to use from one of the three choices.
d with your selection, press the
key
to return
the HF-VHF
2) Press the SET button repeatedly until the SELECT COUPLER page
appears.
upler(s) have a corresponding output labeled FWD (Forward) and REFL
1) Press the ENTER key to cycle through the available choices. When you
cted). Connect the desired couplerare
to satisfied
the FWDwith
and
REFL
input connectors
your
selection,
press the HF-VHF key to return to the
HF-VHF page.
d on the rear panel.
2) The coupler(s) have a corresponding output labeled FWD (Forward) and
REFL (Reflected). Connect the desired coupler to the FORWARD and
NOTE: FOR MAXIMUM ACCURACY, ALLOW AT LEAST A 30
REFLECTED input connectors located on the rear panel.
MINUTE WARM-UP PRIOR TO MAKING ANY MEASUREMENT.
3) Connect the signal to the coupler input port, labeled as RF IN or XMTR
IN.
ct the signal to the coupler input
labeled
as RFofINthe
orcoupler
XMTR labeled
IN.
4) port,
Connect
the output
LOAD or RF OUT to the load.
5) Press
the or
HF-VHF
key to
until
theload.
desired power measurement page is
ct the output of the coupler labeled
LOAD
RF OUT
the
displayed. See Table 3.1 for available choices.
he HF-VHF button until the desired
power measurement page is
6) The power measurement along with any additional data will be
ed. See Table 2.1 for available choices.
displayed:
wer measurement along with any
nal data will be displayed:
DPM6000 Appnote V4 .pages
Page 18
(c) preciseRF 2013-2016
CAUTION: DO NOT EXCEED THE MAXIMUM
SENSOR INPUT POWER LIMITS.
p r e c i s e R F
2.
D P M 6 0 0 0
P O W E R
M E T E R
The MWSD6 sensor shown in Figure 3.2 employs a 50 ohm strip line microwave design. The detector is a Schottky diode selected for exceptional low reverse recovery
time, very low series inductance and low stray capacitance. This configuration allows
detection
at microwave
frequencies.
SuchMEASUREMENTS
a diode is physically very small as seen in the
MICROWAVE
SENSOR
MWSD6
close-up at right. As the demand and manufacturing
The MWSD6 sensor shown in Figure 3.2
volume is limited, each MWSD6 sensor must be hand
employs a 50 ohm strip lline microwave design.
assembled and soldered under a microscope using
The detector is a Schottky diode selected for
SMD manufacturing processes and manually tested.
exceptional low reverse recovery time, very low
The inductance
MWSD6 microwave
(MW)
sensor
features a
series
and low
stray
capacitance.
bandwidth
to
6
GHz.
The
input
is
a
microwave
SMA
This configuration allows detection at
connector
andfrequencies.
the output cable
is connected
microwave
Such
a diode isto the
corresponding
MW
SENSOR
input
on the at
physically very small as seen inlocated
the close-up
DPM6000
frontdemand
panel. The
microwave
detector diode
right. As the
and
manufacturing
has a limited power handling capability. It is important
volume is limited, each MWSD6 sensor must be
!U
s e limits
r ’ s printed
G u ion
d the
e sensor
- A p p l i c a t i o n
to observe the
power
hand assembled and soldered under a
label.
microscope using SMD manufacturing
(a) with
Connect
MWSD6Microwave
sensor to theSensor
MW
processes
andthe
manually
tested.
2. Making a measurement
the
MWSD6
(MS)
N o t e
SENSOR input jack located on DPM6000 front
panel.
CAUTION: DO NOT EXCEED THE MAXIMUM
SENSOR
INPUT
POWER
LIMITS.
(b) Select
the MW
sensor
by pressing
the INPUT
button.
The MWSD6 sensor
shown
in microwave
Figure
3.2source
employs
a 50
ohm stripaline microwave deConnect
the signal
the
MWSD6
The(c)
MWSD6
(MW)tosensor
features
sensor
input.
this
point,
the
sign. The detector is bandwidth
a Schottky
diode
selected
for exceptional
low reverse recovery
Figure 3.2 MWSD6
toSMD
6GHz.
TheAtinput
is a microwave
measurement
result
will
be
displayed.
See
time, very low series SMA
inductance
and
low
stray
capacitance.
This
configuration
allows Sensor
Microwave
connector and the output cable is
Figure
3.2the
MWSD6
below:
detection at microwave
frequencies.
Such
a diode is physically
very small as seen in
connected
to the
corresponding
MW SENSOR
Microwave Sensor
input
locatedand
on manufacturing
the DPM6000 front panel. The
close-up at right. As the
demand
microwave
diodebehas
a limited power
volume is limited, each
MWSD6detector
sensor must
hand
handling
capability.
It
is
important
to observe
assembled and soldered under a microscope using
the power limits
printed on
the sensor label.
SMD manufacturing processes
and manually
tested.
The MWSD6 microwave (MW) sensor features a
PROCEDURE
bandwidth to 6 GHz. The input is a microwave SMA
3) Connect the MWSD6 sensor to the UHF SENSOR input jack located on
connector and the output cable is connected to the
DPM6000 front panel.
corresponding MW SENSOR input located on the
4)The
Select
the UHF
sensordiode
by pressing the UHF key.
DPM6000 front panel.
microwave
detector
DPM6000 POWER METER
has a limited power handling
capability.
It is important
5) Connect
the MSSD6
sensor to the front panel SENSOR input.
to observe the power limits printed on the sensor
6) Connect the signal source to the MWSD6 sensor SMD input. At this
label.
point, the measurement result will be displayed. See below:
(a) Connect the MWSD6 sensor to the MW
SENSOR input jack located on DPM6000 front
panel.
(b) Select the MW sensor by pressing the INPUT
button.
(c) Connect the signal source to the MWSD6
Page 19
this point, the
measurement result will be displayed. See
below:
DPM6000
Appnote
.pagesAt
sensor
SMDV4input.
(c) preciseRF 2013-2016
Figure 3.2 MWSD6
Microwave Sensor
p r e c i s e R F
D P M 6 0 0 0
P O W E R
3. CALIBRATING THE MICROWAVE
!U s e r ’ sSENSOR
G u i d e
M E T E R
-
A p p l i c a t i o n
N o t e
PROCEDURE
3. To Calibrate the Microwave Sensor (MS)
1) Connect a calibration source such as PWR REFERENCE provided on
(a) Connect a calibration source such as
the front panel of the DPM6000 to the MWSD6 microwave sensor SMD
POWER REF provided on the front panel of
input.
the DPM6000 to the microwave sensor input
2) Select
the UHF
SMD input.
See SENSOR
Figure 3.3. input by
pressing the UHF key. Press the
(b)UHF
Select
theagain
MW sensor
input by pressing the
key
and the
UHFT
button.
Press
the
UHFT button again
calibration prompt will appear:
and the calibration prompt will appear:
Figure 3.3 Power Reference
3) At this point you can cancel the calibration procedure by pressing the
key
again
proceed
with
(c)UHF
At this
point
youor
can
cancel the
calibration
the
calibration
by
pressing
procedure by pressing the UHFT key again or
ENTER.
proceed with the calibration by pressing the
ENTER
4) Turn
the key.
PWR REFERENCE on. It
outputs
a
precise 0 dBm (1 mW)
(d) Turn the POWER REF on. The POWER REF outputs a precise
50 MHz signal.
0.00 dBm (1 mW) 32 MHz signal.
5) Use the up/down keys to adjust
(e)the
Use
the "
(up) andto#
(down)
power
reading
0.00
dBm.keys to
adjust the power reading to 0.00 dBm.
6) Press the ENTER button to return
(f) toPress
the ENTER
button todisplay.
return to the MW
the MW
measurement
measurement
display.
The
signal
parameters
The signal parameters must be within
the MWSD6 specifications.
must be within the MWSD6 specifications
See figure 3.2.
Item
MWSD6 Microwave Sensor Specification
Maximum input
power
100 mw
Sensor power range
-20 dBm to + 20 dBm
Enhanced power
range DPM6000 digital RF power meter
option
-30 dBm to + 20 dBm
Bandwidth
2 MHz - 6 GHz
Uncertainty at 15-35
deg. C
+/- 0 .5 dB
Port
SMA
Table 3.2 MWSD6 Microwave Sensor Specifications
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
Page 20
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
4. MAKING FREQUENCY MEASUREMENTS
The DPM6000 incorporates a 100 MHz frequency counter. It can measure
the FORWARD input frequency (located on the rear panel) or measure the
frequency directly using the front panel FREQ INPUT.
!U s e r ’ s
G u i d e
-
A p p l i c a t i o n
N o t e
5.
MEASURE THE FREQ COUNTER INPUT FREQUENCY
4. Making Frequency Measurements
The DPM6000 incorporates a 100 MHz frequency counter. It can measure the FOR-
PROCEDURE
WARD input frequency (located on the rear panel) or measure the frequency directly using
1) Press the FREQ key to display the FREQ page.
the front panel COUNTER input.
Connect
the frequency
source
5. 2)
Measure
the Counter
Input Frequency
directly to the front panel INPUT
(a)
Press FREQ.
the FREQ
button
to displaywill
thebe
labeled
The
frequency
COUNTER
input
page
displayed.
(b) Connect the frequency source directly to
the front panel input labeled COUNTER.
6. MEASURE THE RF INPUT
(FORWARD)
FREQUENCY
(c) The frequency
will be displayed.
6. PROCEDURE
Measure the RF Input (FWD) Frequency
1) Press the FREQ key until the display
(a) Press the FREQ button until the display
indicates - RF INPUT (FWD) - input
indicates - RF INPUT (FWD) - input
page
is displayed.
page is displayed.
2) Connect the frequency source directly
(b) Connect the frequency source directly to the forward input (located on the rear
to the FORWARD input (located on the rear panel). You must have
panel.) You must have sufficient signal amplitude and a continues carrier for the
sufficient signal amplitude and a continuous carrier for the counter to
counter to make the measurement. Note, this measurement is very difficult with
make
the measurement. The frequency will be displayed.
SSB modulation.
NOTE:
This measurement
is very difficult with SSB modulation.
(c)
The frequency
will be displayed.
DPM6000 Appnote V4 .pages
DPM6000 POWER METER
Page 21
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0 P O W E R M E T E R
!U s e r ’ s G u i d e - A p p l i c a t i o n
N o t e
VI.
M E A S U R E M E N T C O N S I D E R AT I O N S
IV. Measurement limits
1. System Specifications
The DPM6000
widerange
dynamic
range
log with
amplifiers
with a of 10
The DPM6000
uses wideuses
dynamic
(90dB)
log(90dB)
amplifiers
a bandwidth
bandwidth of 10KHz to 500 MHz. These log amplifiers have specified
KHz to 500 MHz. These log amplifiers have specified linearity and accuracy specifications.
linearity and accuracy specifications. Couplers have a typical bandwidth
Couplers havefrom
a typical
bandwidth
from
1 MHz to on
150power
MHz depending
on other
powerfactors.
handling
1 MHz
to 150 MHz
depending
handling and
and other factors.
couplers
do have
not have
detectors
couple
a small
portion
of the
Also,Also,
couplers
do not
detectors
andand
couple
a small
amount
of the
RF RF
energy
(generally
between
-20
dB
to
45
dB)
to
the
FORWARD
and/or
signal (generally between -20 dB to - 45 dB) to the FORWARD and/or REFLECTED outputs.
REFLECTED outputs. On the other hand, sensors contain detectors, either
On the other hand, sensors contain detectors, either as a diode or thermal detector. This
as a diode or thermal detector.
detector converts the diode’s rectified energy in a DC voltage or the thermal energy into a
DC voltage. These detectors can have bandwidth ranging to many GHz. For example, the
This detector converts the diode’s rectified energy in a DC voltage or the
-19.00 0.00379
6.2095
0.8500 0.000027
-15.74 1.2074
-19.00
PreciseRF MWSD6
of
2These
MHz
6 GHz
with
ahave
sensitivity
dBm1.2009
to
thermalSensor
energyhas
intoa abandwidth
DC voltage.
detectors
can
bandwidth
-20.00
0.00309 to
5.0627
0.7000
0.000022
-16.62
1.2031-30
-20.00
1.2003
-21.01 0.00250
4.0960
0.5900 0.000018
-17.54 1.1976
-21.01
1.2011
ranging
many GHz.measurement
For example,
the PreciseRF
MWDS6
Sensor
a 1.2039
-22.01 accuracy,
0.00206
3.3751 the
0.4400
0.000015
-18.38 1.1972has
-22.01
+ 20 dBm. Thus,
whentoconsidering
individual
components
-23.00 0.00172
2.8180
0.3400 0.000012
-19.17 1.1999
-23.00
1.2088
-24.00
0.00142
2.3265
0.3000 0.000010
-20.00
1.2000 Thus,
-24.00
1.2009
2 MHz to 6 system
GHz with
a sensitivity
of
-30dB
yo + 20
dBm.
comprising thebandwidth
entire measurement
must
be
taken
into
account.
-25.00 0.00119
1.9497
0.2300 0.000008
-20.77 1.2038
-25.00
1.2003
-26.00
0.00100
1.6384
0.1900
0.000007
-21.52
1.2080
-26.00
when considering measurement accuracy, the individual components must 1.2011
-27.00 0.00085
1.3926
0.1500 0.000006
-22.23 1.2146
-27.00
1.2039
-28.00 0.00074
1.2124
0.1100 0.000005
-22.83 1.2264
-28.00
1.2088
be taken
into account.
2. Square Low
Sensor
-29.01
-30.00
0.00064
0.00057
1.0486
0.9339
0.1000
0.0700
0.000005
0.000004
-23.46
-23.96
1.2365
1.2519
-29.01
-30.00
1.2149
1.2235
Because of the resolution limits
Sensor square law output dBm / Vout
Square Low Sensor.
2.50000
(12 bit) of the analog to digital
Because of the resolution
converter installed
the
DPM6000,
limits in
(12
bit)
of the
2.00000
the total rangeanalog
measured
may
to digital be
convertercan
installed
less than the MWSD6
deliver.in the
1.50000
DPM6000, the total
This is because of the square law
range measured may be
V out
1.00000
and logarithmic
dv/dBm
less
than the MWSD6
This
is
relationship. Acan
highdeliver.
dynamic
range
0.50000
the square
measurementbecause
option forofthe
law and logarithmic dv/
DPM6000 is available which
0.00000
dBm relationship. A high
-40.00
-30.00
-20.00
-10.00
0.00
10.00
20.00
30.00
extends the lower
measurement
dynamic range
measurement
option for
limit by an additional
10 dBm.
the DPM6000 is available Figure 4.1 Square Law Sensor Logarithmic Response
3. Measurement
whichuncertainty
extends the lower measurement limit by an additional 10 dBm.
All measurements are subject to
uncertainty1.and
a measured valueUNCERTAINTY
is only complete if it is accompanied by a statement of
MEASUREMENT
the associatedAlluncertainty.
Relative
is the measurement
uncertainty
measurements
are uncertainty
subject to uncertainty
and a measured
valuedivided
is onlyby
the measuredcomplete
value. if it is accompanied by a statement of the associated uncertainty.
Relative uncertainty is the measurement uncertainty divided by the
No measurement
is exact.
measured
value. When a quantity is measured, the outcome depends on the
measuring system, measurement procedure, skill of the operator, the environment, and
other effects. Even if the quantity were to be measured several times in the same way and in
DPM6000 Appnote V4 .pages
Page 22
DPM6000 POWER METER
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
No measurement is exact. When a quantity is measured, the outcome
depends on the measuring system, measurement procedure, skill of the
operator, the environment, and other effects. Even if the quantity were to be
e r ’ s way
G uand
i d ein -theA same
p p l i circumstances,
c a t i o n N o t ea
measured several times in!U
thes same
different measured value would, in general, be obtained each time,
assuming
the measuring
has
sufficient
resolution
to obtained
distinguish
the same
circumstances,
a differentsystem
measured
value
would, in
general, be
each
between
the
values.
The
dispersion
of
the
measured
values
would
relate
to
time, assuming the measuring system has sufficient resolution to distinguish between the
how well the measurement is made. Their average would provide an
values.
estimate of the true value of the quantity that generally would be more
Thereliable
dispersion
of an
the individual
measured values
wouldvalue.
relate to how well the measurement is
than
measured
made. The
Theirdispersion
average would
an estimate
of the truevalues
value ofwould
the quantity
that
andprovide
the number
of measured
provide
generally
would be more
reliable
thanaverage
an individual
measured
value. The
and the
information
relating
to the
value
as an estimate
of dispersion
the true value.
number of measured values would provide information relating to the average value as an
estimate of the true value.
2. CUMULATIVE EFFECT OF UNCERTAINTY ON MEASUREMENTS.
4. Cumulative
Effect of is
Uncertainty
onthe
Measurements
Total uncertainty
the sum of
cumulative addition of all uncertainties. It
is uncertainty
this worst case
uncertainty
on which
manufacturers
base their
Total
is the sum
of the cumulative
addition
of all uncertainties.
It is this worst
specifications.
Fortunately,
typically
not
all
uncertainties
add
up
in the same
case uncertainty on which manufacturers base their specifications. Fortunately, typically
not
direction,
and
generally
have
a
random
value
distribution.
For
example,
an
all uncertainties add up in the same direction, and generally have a random value
attenuator might be .01dB high and the sensor might be 0.01 dB low, or one
distribution. For example, an attenuator might be .01dB high and the sensor might be
system might have a positive temperature coefficient while another might
0.01 dB low, or one system might have a positive temperature coefficient while another
have a negative temperature coefficient. In the examples given, one
might have
a negative
temperature
coefficient.
In the For
examples
given, one
uncertainty
factor
may cancel
the other.
this reason,
theuncertainty
ultimate factor
may cancel
the other.
this reason
the ultimate
as for
it relates
uncertainty
is
accuracy
as itFor
relates
to uncertainty
isaccuracy
adequate
all butto the
most stringent
adequate
for all but the most stringent requirements.
requirements.
Cal Standard
Uncertainty
Total Uncertainty
NIST Standard
0.1%
0.1%
Aging
Transfer Standard
0.4%
0.5%
Transfer coupling
instrument error
Delivered from Manufacturer
1%
1.5%
Transfer coupling
instrument error
Log amp error(s)
1%
2.5%
Component tolerance temperature
1.5%
4%
Component tolerance temperature
1%
5%
Calibration
techniques, QC
Sensor error(s)
Final Specification
(Conservative)
Causes
Table 4.1 Measurement Uncertainty
Table 4.1 Measurement Uncertainty
DPM6000 Appnote V4 .pages
DPM6000 POWER METER
Page 23
(c) preciseRF 2013-2016
5. Maximizing Measurement Certainty
See Figure 4.2. These two instruments appear to agree within 6 parts out of 5,248, that
is better than 0.11 %. At first glance, that is a remarkable result, especially when
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
considering that the measurement taken by a Precise RF DP1A was with an in-line coupler,
and the HP 338A was taken with a power attenuator. How is that possible? Neither
instrument specifications
are even close
to 1%.
3. MAXIMIZING
MEASUREMENT
CERTAINTY
One
cannot
conclude
See Figure
4.2.
These
two
that the appear
actual power
instruments
to agree
52.48
Watts or
within delivered
6 parts is
out
of 5,248,
Watts.
that is 52.42
better
thanIt might
0.11 very
%. At
well be, that
but we
first glance,
iscan’t
a be
certain
of
it.
The
only certain
remarkable result, especially
conclusion one that
may gather
when considering
the
from this experiment
measurement
taken byisathat
both
are with
withinan
Precise
RFinstruments
DP1A was
uncertainty
in-line their
coupler,
and the HP
specifications
(assuming
338A was
taken with
a power
they were
calibrated
attenuator.
How
is that
correctly).
This
uncertainty is
possible? Neither instrument
Figure 4.2 Power Measurement Comparison, PreciseRF DP1A & HP438A
typically 5%
when
including
specifications
are
even
closeall the
cumulative
factors
in
the
measurement
to 1%. One cannot conclude
system.
that the
actual power delivered is 52.48 Watts or 52.42 Watts. It might very
well be,
but we can’t be certain of it.
6. Temperature Effects
Many engineers,
rightfully
so, may
consider
the HP438A
alongexperiment
with the HP sensors
The only certain
conclusion
one
gather
from this
is thatasboth
industry
standards.
In
this
experiment,
a
high
power
attenuator
was
employed
to reduce
instruments are within their uncertainty specifications (assuming they
were the
calibrated
This uncertainty
is typically
5% when
all the
signalcorrectly).
level to a manageable
level. As it turns
out, the NARDA
SETl including
769.20 150 Watt
power
cumulative
factors
in athe
system. coefficient affecting the attenuation
attenuator
exhibits
verymeasurement
slight negative temperature
factor. It is dissipating 52.48 Wat and is warm to the touch. On the other hand, while the
PreciseRF DPM6000 DDC-2KW in-line coupler also exhibits a very slight temperature
4. TEMPERATURE EFFECTS
coefficient, it dissipated just 1.6 mW, which is so low that it did not impact this measurement
Many engineers,
rightfully so, consider the HP438A along with the HP
at all.
sensors as industry standards. In this experiment, a high power attenuator
While the power reading using the HP438A required some time to settle as the
was employed
to reduce the signal level to a manageable level. As it turns
attenuator temperature stabilized, the PreciseRF DPM6000 did not exhibit this effect. Had
out, the NARDA SETl 769.20 150 watt power attenuator exhibits a very slight
the power been greater, for example 1,500 Watts, the coupler would have had to dissipate
negative
temperature coefficient affecting the attenuation factor. It is
dissipating 52.48 watt and is warm to the touch. On the other hand, while the
METER
PreciseRF DPM6000 DDC-2KWDPM6000
in-line POWER
coupler
also exhibits a very slight
temperature coefficient, it dissipated just 1.6 mW, which is so low that it did
not impact this measurement at all. While the power reading using the
HP438A required some time to settle as the attenuator temperature
stabilized, the PreciseRF DPM6000 did not exhibit this effect. Had the power
been greater, for example 1,500 watts, the coupler would have had to
dissipate. Note about 50mW (assuming continuous power), in which there
may also have been a very slight temperature effect on the measurement
during warm-up.
The ability to perform a field calibration in an RF power measurement system
contributes greatly to reducing the measurement uncertainty. Even the
vintage Heathkit HM-102 power meter allows users to calibrate the meter to
at least 5% of full scale. The Bird 43 couplers/elements can also be
DPM6000 Appnote V4 .pages
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M E T E R
calibrated to 5% of full scale, but that requires the disassembly of the in-line
coupler. To reduce measurement uncertainty, the single most important item
is a known accurate POWER REFERENCE source. Most lab accurate RF
power meters and the PreciseRF DPM6000 include this capability.
DPM6000 Appnote V4 .pages
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p r e c i s e R F
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M E T E R
VII. M E T R O L O G Y P R A C T I C E S
It is good metrology and engineering practice, when making measurements
of key parameters, to confirm the results. When confirming the measurement
results, one excellent way is to use more than one measurement instrument
and or technique. Aside from the techniques used at NIST, field RF power
measurements can be done using an oscilloscope, spectrum analyzer,
simple analog power meters and dedicated power meters such as the
DPM6000. In the real world, comparing RF power with a number of methods
and arriving with the same, or nearly identical results, decreases
measurement uncertainty and increases confidence. However, it is important
to understand all the factors affecting the measurement chain. This is
especially true when making low power measurements (less then -40 dBm).
At these low power levels, thermal noise and interfering RF energy can play
havoc.
1. SPECTRUM ANALYZER
Also, remember that most power meters measure broadband power, and not
necessarily the signal power in which you might be interested. A high quality
spectrum analyzer is especially well suited for these low level signals. The
frequency versus power (dBm) graph shown on a spectrum analyzer, helps
in identifying interfering RF sources.
2. OSCILLOSCOPE
Just like the spectrum analyzer, an oscilloscope allows you to take a look at
the power waveform. An oscilloscope is useful in examining the power
waveform (taking into consideration the scope’s bandwidth). When viewing
the signal shape, we look at it in the time domain and can measure
amplitude, shape, and power (using a suitable termination). When using the
FFT (Fast Fourier Transformation) available on most modern DSO scopes, of
sufficient bandwidth, we can identify the power spectrum. Note interfering
signals in the frequency domain. Also, keeping in mind the scope’s vertical
amplifier bandwidth, the waveform can be examined for amplitude and
purity.
3. ANALOG POWER METER
One often overlooked instrument is a simple power meter like the Bird 43.
Since its accuracy is generally just 5% of full scale, you can at least confirm
that your measurement is in the right ball park. Beside the Bird 43, there are
a number of inexpensive analog power meters which will give you a fairly
DPM6000 Appnote V4 .pages
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good indication within a few percent. But remember, most of these meters
use in-line couplers and diode detectors and do not lend themselves to low
level power measurements.
So why were the PreciseRF DPM6000 and HP 438A meters so close in their
readings? Here is the answer. Our calibration procedure for the DPM6000
calls out the HP438A (traceable to NIST) as a POWER REF. Also, the field
calibration was accomplished (described elsewhere in this user guide) in
our lab, using the NARDA model 769.20 150 watt power attenuator and
HP438A as a reference when calibrating the log amplifiers and couplers/
sensors. It is not surprising to note that the two power meters agree as
closely as they do. So, this was just a test on how well I performed the
calibration procedure using the HP438A as a reference.
DPM6000 Appnote V4 .pages
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VIII. F I E L D C A L I B R A T I O N
The DPM6000 is factory calibrated using NIST traceable instruments.
However, by using the POWER REFERENCE, instrument accuracy and
measurement certainty can be improved considerably. If accuracy of better
than 0.5dB is sufficient for your measurement, the forward (FWD), reflected
(REFL) and microwave sensor can be calibrated using the POWER
REFERENCE. This is referred to as “field calibration”. Unless the POWER
REFERENCE is itself out of calibration - in which case it needs be calibrated
using the factory calibration procedure - the measurement accuracy and
uncertainty level can approach the accuracy of the POWER REFERENCE.
See Factory Calibration elsewhere in this guide.
1. CALIBRATION OF FORWARD AND REFLECTED GAIN
While the primary gain was adjusted during the factory calibration (explained
in detail elsewhere in this guide), variation in coupler sensitivity, frequency,
temperature and cable losses can compromise the accuracy of the overall
measurement. For this reason, a field calibration method is provided. The
calibration routine can use either the internal power reference POWER REF,
or a separate external calibration source. The calibration accuracy is
primarily limited by the POWER REF signal accuracy. Using the POWER REF
will provide an overall accuracy of better than +/- 0.2 dB.
2. CALIBRATING THE DPM6000 WITH THE PWR REFERENCE
PROCEDURE
1) Turn the DPM6000 and the PWR REFERENCE on. Let it warm up for at
least 30 minutes. This stabilizes the DPM6000.
2) Using the SET key, navigate to the SELECT COUPLER page.
3) Set the COUPLER choice to 0dB NONE
(2W MAX).
NOTE: use the ENTER key to cycle
through the three choices.
4) Press the SET key to continue.
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5. CALIBRATING THE FORWARD GAIN
PROCEDURE
1) Connect a high quality BNC cable from the PWR REFERENCE output
(or an external 1mW 0dBm calibrator) to the FORWARD input on the rear
panel. Insure the PWR REFERENCE is still on.
2) Using the SET key, select the
CALIBRATE FORWARD GAIN page.
3) Press the ENTER key to begin the
calibration procedure.
4) Using the up/down keys, set the
displayed value equal to the PWR
REFERENCE.
NOTE: the example illustrates a calibration source from the PWR
REFERENCE with a 1mW / 0dBm signal level compensated for any
cable and connector losses. If your calibration source is a different level,
then the level should be adjusted to equal that calibration source.
5) When the value equals the PWR REFERENCE press the ENTER key.
After pressing ENTER, you will be prompted with the required steps to
calibrate the REFLECTED gain.
4. CALIBRATING THE REFLECTED GAIN
PROCEDURE
1) Connect a high quality BNC cable from the PWR REFERENCE output
(or an external 1mW 0dBm calibrator) to the REFLECTED input on the
rear panel. Insure the PWR REFERENCE is still on.
2) Using the SET key, select the CALIBRATE REFLECTED GAIN page.
3) Press the ENTER key to begin the calibration procedure.
4) Using the up/down keys, set the
displayed value equal to the PWR
REFERENCE.
5) NOTE: the example illustrates a
calibration source from the PWR REFERENCE with a 1mW 0dBm signal
level compensated for any cable and connector losses. If your
calibration source is a different level, then the level should be adjusted to
equal that calibration source.
6) When the value equals the PWR REFERENCE, press the ENTER key.
The calibration is complete.
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5. CALIBRATING THE DPM6000 WITH COUPLER(S)
The directional couplers are available with a coupling coefficient of -30dB
and -45dB to accommodate higher transmitter powers. The coupler
coefficient accuracy is better than +/- 1dB. If the DPM6000 was calibrated at
0dB (no coupler) described previously, no calibration is necessary for
nominal accuracy since accuracy will be determined by he coupler
coefficient. For the highest resolution and accuracy you can calibrate/
normalize the DPM6000 and selected coupler and cables as a system.
However, this requires a higher power calibration source. It should be
capable to output a stable high accuracy 10MHz signal at least
40dBm(10Watts) into 50 ohms.
When calibrating couplers, connect the coupler’s FORWARD and
REFLECTED outputs to the respective FORWARD and REFLECTED input on
DPM6000 rear panel using BNC cables.
PROCEDURE
1) Apply the signal source to the coupler’s RF INPUT. Make certain the RF
OUTPUT is terminated into a 50 ohm dummy load.
NOTE: These instructions illustrate calibrating a -45 dB coupler.
2) Using the SET key, navigate to the SELECT COUPLER page.
3) Set the COUPLER choice to -45dB.
Note, use the ENTER keyto cycle
through the three choices. Use the SET
key to continue.
4) The FORWARD GAIN page will be
displayed. Press the ENTER key to
begin the calibration procedure
5) Using the up/down keys, adjust the
displayed value to equal the level of your
calibration signal source. For example,
with a -45dB coupler selected and the
coupler connected to the external signal
generator outputting a 45dBm (31.62 W)
signal, adjust the reading for 45dBm.
DPM6000 Appnote V4 .pages
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e r6 ’ 0s 0 G
l i Tc Ea R
t i o n
p r e c i s e R F !U
D Ps M
0 u Pi dOeW -E RA p Mp E
N o t e
MICROWAVE
SENSOR
4. To Calibrate 6.
theCALIBRATE
Microwave THE
Sensor
(MS)
This procedure was previously described in the section covering “Making a
measurement with the MWSD6 Microwave Sensor (MS)”. It is repeated here
ment with the MWSD6
Sensor
(MS)”.
It is the
repeated
for Microwave
users needing
to only
calibrate
sensor.here for users needing to
This procedure was previously described in the section covering “Making a measure-
only calibrate the sensor.
PROCEDURE
(a) Connect a calibration source such as
1) Connect a calibration source
POWER REFsuch
provided
on REFERENCE
the front panel of
as PWR
the DPM6000provided
to the microwave
on the front sensor
panel ofinput
the
DPM6000
to
the
microwave
SMD input. See figure 5.1
sensor input SMD input. See
figure
5.1 input by pressing the
(b) Select the MW
sensor
UHFT button.
Pressthe
theUHF
UHFT
buttoninput
againby
2) Select
SENSOR
pressing
the UHF
Press the
and the calibration
prompt
will key.
appear:
UHF key again and the
prompt
will
appear:
(c) At this point, calibration
you can cancel
the
calibration
procedure3)byAtpressing
theyou
UHFT
key again,
this point,
can cancel
the
or proceed with
the calibration
by by
pressing
calibration
procedure
pressing
the UHF key again, or proceed
the ENTER key.
Figure 5.1 Power Reference
with the calibration by pressing
the ENTER
key.The POWER REF
(d) Turn the POWER
REF on.
outputs a4)
precise
Turn the PWR REFERENCE on. It
precise
0.00 dBm (1
0.00 dBm (1 outputs
mW) 32aMHz
signal.
mW) 50 MHz signal.
(e) Use the "
# (down)
keys
to
5) (up)
Use and
the up/down
keys
to adjust
adjust the power
reading
to 0.00
the power
reading
to dBm.
0.00 dBm.
Press button
the ENTER
button
(f) Press the6)ENTER
to return
to to
thereturn
MW
to the - MICROWAVE SENSOR measurementmeasurement
display. Thedisplay.
signal parameters
The signal
must be within
specifications.
willthe
beMWSD6
displayed.
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IX. F A C T O R Y C A L I B R A T I O N
!U s e r ’ s
G u i d e
-
A p p l i c a t i o n
N o t e
calibration
procedure assumes that the DPM6000 is not in need of
VI.This
Factory
Calibration
repair. If you do not have the equipment and or knowledge to perform the
With the right test equipment and technical skill, a “factory” calibration can be done in
calibration, we suggest you return the DPM6000 to PreciseRF for factory
your lab or by an authorized factory service center. This calibration procedure assumes that
calibration.
the DPM6000 is not in need of repair. The case of the DPM6000 is sealed. Breaking the seal
NOTE:
MAXIMUM
DPM6000
ON yourself,
AND LET
IT
may voidFOR
the calibration
and ACCURACY
warranty. If you TURN
want to THE
calibrate
the DPM6000
please
WARM-UP
FOR so
ATwe
LEAST
30 MINUTES.
THIS
LOG and a
contact PreciseRF,
can arrange
to provide you
withSTABILIZES
any additional THE
instructions
AMPLIFIERS
AND
PWR
REFERENCE.
replacement seal.
If you
do not
have the equipment and or knowledge to perform the
calibration, we suggest you return the DPM6000 to PreciseRF for calibration.
1. EQUIPMENT
REQUIREMENTS
1. Equipment Requirements:
Quantity & Item
Model
3 - Cable 50 Ohm
50 ohm RG58 3 feet
2-Terminator 50 ohm
1/4 W Tektronix 011-0049-01 or equivalent
1-Step Attenuator
precise RF step attenuator AT1502W DC-1GHz
50 ohm
2- Fixed Attenuator
Tektronix 10X (20dB) 50 ohm 2 W
011 0059-01
1- Power meter
HP Power meter HP 438A or equivalent
1- Power Sensor
HP Power sensor 8484A power sensor 50 ohm .
3nW - 10 uW
1 - Attenuator
30 DB 50 OHM 90513 STODDARD
fixed attenuator.
1 - Spectrum Analyzer
Rigol 1030 3GHz spectrum analyzer or
equivalent
1 - Digital Voltmeter
Digital Voltmeter Fluke model 83 Voltmeter accuracy ±(0.1%+1) or equivalent
1 - Oscilloscope
Oscilloscope 200 MHz Tektronix TDS2022C or
equivalent
1- Frequency Counter
B&K 1856D 3.5 GHz Frequency Counter or
equivalent
Firmware
If the firmware needs upgrading, you need a
Windows XP compatible computer and
PICkit(TM) 3 Programmer along with the latest
firmware.
Table 6.1 Equipment Requirements
DPM6000 POWER METER
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!U s e r ’ s
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P O W E R
-
A p p l i c a t i o n
N o t e
M E T E R
NOTE: MANY CALIBRATION STEPS ARE INDICATED
WITH PROMPTS ON THE DPM6000 DISPLAY.
2. ADJUST THE 10,000,000HZ
CLOCK DUTY CYCLE
The clock for the frequency counter and microprocessor share a
temperature
compensated
precision
MHz
1. Adjust
the 10,000,000
Hz Clock 10
Duty
Cycletime base. For proper
operation, the The
duty
cycle of the output of the time base must be set to 50%
clock for the frequency counter and microprocessor share a temperature
+/- 5%. Thecompensated
frequencyprecision
resolution
oftime
thebase.
counter
is two
(2) Hz.
10 MHz
For proper
operation,
the duty cycle of the
output of the time base must be set to 50% +/- 5%. The frequency resolution of the
counter is two (2) Hz.
PROCEDURE
Connect
a cable
from Clock
1) Connect a (a)
cable
from
CLOCK
output to an Oscilloscope
output to an Oscilloscope.
Adjust
Adjust the scope for a stable
the scope for a stable display.
display.
2) The amplitude should be
CLOCK OUT
approximately 2.5Figure
VPP.6.1Observe
(b) The
amplitude should be
waveform duty
cycle.
NOTE: The
approximately 2.5 VPP. Note
the waveform
duty cycle
of this waveform.
The duty
may be different than
duty
cycle may
be different
than the
onecycle
shown.
the one shown.
3) Adjust R3 for a duty cycle of 50% +/- 5%. See Figure 6.2. Depending on
(c) Adjust R3 for a duty cycle of
the scope and50%
probe
the 6.2.
waveform may have more or less over+/- 5%.used,
See Figure
shoot or aberrations.
The important
factor is the duty cycle.
Note: Depending
on the
scope and probe used, the
waveform may have more or
less overshoot or aberrations.
The important factor is the
duty cycle.
Figure 6.2 Duty Cycle Adjustment 50%
DPM6000 POWER METER
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M E T E R
2. Adjust the 10,000,000 Hz Clock Frequency
The time base is a crystal controlled temperature compensated oscillator. It
features
excellent frequency
stability.
4. ADJUST
THE 10,000,000HZ
CLOCK FREQUENCY
The time base is a crystal controlled
(a) Connect the clock output located at the
temperature compensated oscillator. It
DPM6000 rear panel to a precision counter
features excellent frequency stability.
with at least 1 Hz resolution at 10,000,000 Hz
and accuracy better than 1 part per 10 million.
PROCEDURE
(b) Using
special alignment
adjust
the crystal
to rear
10,000,000
1)a Connect
the Clocktool,
output
located
at theoscillator
DPM6000
panel toMHz
a +/2 Hz. This
requires
some finesse.
Make
you haveatwarmed
up both
precision
counter
with at least
1 sure
Hz resolution
10,000,000
Hz the
and
accuracy
than
perone
10 hour.
million.
DPM6000
and thebetter
Counter
for1atpart
least
a special
alignment
adjust one
the crystal
10,000,000
If you3)doUsing
not have
this tool,
you maytool,
construct
out of aoscillator
jeweler’stoscrew
driver
MHz +/- 2 Hz. This requires some finesse. Make sure you have warmed
and an file. This will require a magnifying glass, as the adjustment socket on the
up both the DPM6000 and the Counter for at least one hour. If you do
oscillatornot
is quite
have small.
this tool, you may construct one out of a jeweler’s screwdriver
and a file. This will require a magnifying glass, as the adjustment socket
3. Calibrate the
2.50 VDC Reference Voltage
on the oscillator is quite small.
These next steps calibrate the 2.500 Volt reference. The microprocessor uses
this reference
to set the
levels
of the Analog
to Digital converter
range. The output of
4. CALIBRATE
THE
2.50VDC
REFERENCE
VOLTAGE
the log amplifiers
is steps
compared
to this
voltage.
The reference.
reference must
be set accurately
These next
calibrate
the
2.500 Volt
The microprocessor
this reference
to set
the levels
of the
Analog
to Digital
converter range.
to realizeuses
the excellent
dynamic
range
available
from
the AD8307
logarithmic
The output of the log amplifiers is compared to this voltage. The reference
amplifiers.
must be set accurately to realize the excellent dynamic range available from
thethe
AD8307
logarithmic
(a) Locate
PGM jack
(J6) on amplifiers.
the main circuit board. Using an alligator clip, short
out J6.
PROCEDURE
(b) With J6 shorted, turn on the
1) Locate the PGM jack (J6) on the main circuit board. Using an alligator
DPM6000.
clip, short out J6. With J6 shorted, turn on the DPM6000.
(c) As the
the up, the display prompts the calibration of the 2.500
2) unit
As powers
the unit up,
powers
display prompts
theadjustment.
calibration
volt (R19)
of the 2.500 Volt (R19)
3) Connect a precision DC voltmeter between ground and J5 and adjust
adjustment.
R19 to precisely 2.500 volts DC. Press ENTER to continue.
(d) Connect a precision DC voltmeter between ground and J5 and adjust R19 to
precisely 2.500 Volts DC.
(e) Press ENTER to continue.
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
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!U s e r ’ s
5. CALIBRATE THE KEYPAD
P O W E R
G u i d e
-
M E T E R
A p p l i c a t i o n
N o t e
Each key has a unique voltage which identifies the key. These next steps
4. Calibrate
the Keypad
interrogate
the keypad voltages used by the microprocessor. Should you
Each
key has
a unique voltage
which identifies
the key. These
next steps
make
a mistake,
just re-start
the calibration
beginning
withinterrogate
step 3 above.
the keypad
microprocessor.
you make aifmistake,
You voltages
do not used
needbytothe
adjust
the 2.500Should
volt reference
is was just
calibrated
re-startpreviously.
the calibration beginning with step 3 above (you do not need to adjust the 2.500
Volt reference if is was calibrated previously). Note, that each time you press a key, a
PROCEDURE
short beep will sound and a number corresponding to that key will be briefly displayed.
(a) After completing the 2.500 Volt adjustment press the # (down) key.
(b) Continue with the calibration and press the SET key.
(c) Continue with the calibration and press the FREQ key.
(d) Continue with the calibration and press the HF-VHF key.
Continue with the calibration and press the UHF key.
(e) Continue with the calibration and press the " (up) key.
(f) Finish the calibration and press the ENTER key.
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
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6. CALIBRATE THE AD8307 LOGARITHMIC AMPLIFIERS
Before calibrating the slope
calibration
!U sas
e rdirected
’ s G u in
i dthe
e next
- A p
p l i c a t istep,
o n the
N o log
t e
amplifiers intercept point must be calibrated. The AD8307 logarithmic
amplifiers are complete 500 MHz monolithic demodulating logarithmic
5. Calibrate the AD8307 Logarithmic Amplifiers
amplifiers based on progressive compression.
Before calibrating the slope as directed in the next calibration step, the log
amplifiers intercept point must be calibrated. The AD8307 logarithmic amplifiers are
7. ADJUST THE FORWARD AND REFLECTED INTERCEPTS
complete 500 MHz monolithic demodulating logarithmic amplifiers based on
progressive compression.
PROCEDURE
1) To
calibrate
the FORWARD
7. Adjust
Forward
Channel
Intercept intercept, remove the shield from the forward
channel.
(a) Remove the shield and connect a known accurate 0 dBm 50 MHz signal source
as the POWER
REF output
2)such
Connect
an accurate
1mW from
50Power
MHz Meter
calibration
an 0dBm
HP436A
or HP 438A
source
such
as the POWER
Power
Meter
to FORWARD
Input
REF
output
from
an
HP436A
located on the rear panel.
power meter or equivalent to
(b) The
POWER
REF ofinput
the DPM6000
the
FORWARD
located
canon
also
used,
assuming
theberear
panel.
If thethat it
hasDPM6000
been previously
PWR calibrated.
REFERENCE
is calibrated it may be used.
(c) Adjust the intercept voltage at J3, to
3)precisely
Adjust2.00
the VDC.
intercept voltage at
J3, to precisely 1.800 VDC.
(d) Replace
the the
shield.
Replace
shield.
Figure 6.4 Forward Channel Intercept
8. Adjust
Reflected
Intercept
4. To
calibrateChannel
the REFLECTED
intercept,
remove
shield
(a) Remove
the shield
andthe
connect
a
from
the
forward
channel.
known accurate 0 dBm 50 MHz signal
such the
as the
POWER
5)source
Remove
shield
fromREF
the
output
from
an
HP436A
Power
Meter or
forward channel.
HP 438A Power Meter to REFLECTED
6)Input
Connect
calibration
locatedthe
on the
rear panel.
source to the REFLECTED
(b) The
POWER
REFon
of the
can
input
located
the DPM6000
rear
panel.
also
be used, assuming that it has
been previously calibrated.
7) Adjust the intercept voltage at
the J7,
to precisely
1.800
(c) Adjust
the intercept
voltage,
at J7 to
VDC.
Replace
the
shield.
precisely 2.00 VDC.
Figure 6.5 Reflected Channel Intercept
(d) Replace the shield.
DPM6000 Appnote V4 .pages
DPM6000 POWER METER
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!U s e r ’ s
G u i d e
8. Calibrate the Analog to Digital Converter Slope
p r e c i s e R F
D P M 6 0 0 0
-
A p p l i c a t i o n
P O W E R
N o t e
M E T E R
This step calibrates the analog to digital converter slope at two signal levels
8. Calibrate the Analog to Digital Converter Slope
which are -40dBm
0 dBm. This
is normally
done after theSLOPE
keypad has
8. and
CALIBRATE
THEcalibration
ANALOG TO
DIGITAL CONVERTER
This step calibrates the
analog
to digital converter
slope
at two
signal
levels levels
step discussion).
calibrates the analog
to digital
converter a
slope
at two signal
been calibrated (seeThis
earlier
For greatest
accuracy,
precision
signal
which are -40dBm and
0 dBm.
This calibration
normally
done
after the
keypad
has
which
are -40dBm
and 0 dBm. is
This
calibration
is normally
done
after the
source should be used,
such
as
the
POWER
REF
output
from
an
HP436A
Power
keypad has been calibrated (see earlier discussion). For greatest accuracy,
been calibrated (see earlier discussion). For greatest accuracy, a precision signal
a precision
signal
should
be of
used,
as the POWER
REF
Meter or HP 438A Power
Meter.
Thesource
POWER
REF
thesuch
DPM6000
can also
beoutput
source should be used,
as theorPOWER
REF output
fromPOWER
an HP436A
from such
an HP436A
HP 438A Power
Meter. The
REF of Power
the DPM6000
used, assuming that it has been previously calibrated.
can also
be used
it has beenREF
previously
skip
Meter or HP 438A Power
Meter.
Theif POWER
of thecalibrated.
DPM6000You
cancan
also
bethe
2.500 VDC calibration and the clock time-base calibration if that has already
(a)
You
can skipthat
the 2.500
VDC previously
calibration calibrated.
and the clock time-base calibration if that
used,
assuming
it has
been
been
done.
has already been done. Repeat the keypad calibration step 5 (a) if needed. This
(a) will
Youonly
can take
skip the
2.500
VDCto
calibration
the clock
time-base calibration if that
a few
minutes
calibrate and
the keypad
again.
PROCEDURE
has already been
done. Repeat the keypad calibration step 5 (a) if needed. This
1) Repeat the keypad calibration step if needed. Once you completed the
(b) Once you completed
the keypad calibration, you
will only take a few keypad
minutescalibration,
to calibrate
again.
youthe
will keypad
be presented
with the display shown.
will be presented with the display shown. Press
2) Press
ENTER
key.
(b) the
Once
you completed
the the
keypad
calibration,
you
ENTER
key.
Thethe
nextdisplay
displayshown.
will prompt
you
will be presented3)with
Press
toprompt
apply -40
dBm
the -40 dBm
(c) The
next display
you
to to
apply
the ENTER
key. willFORWARD
input located on the
to the FORWARD input
located
on the rear panel of DPM6000.
rear panel
of DPM6000.
(c) The next display will prompt you to apply -40 dBm
To create
this signal
level,
you
To create
signal4)level,
you
must
use
an
attenuator
series with the 0 dBm
to the this
FORWARD
input
located
on
the
rear
panel ofinDPM6000.
must use an attenuator in series with the 1mW 0dBm PWR
POWER REF. You can use a precision step attenuator such as a PreciseRF step
REFERENCE. You can use a precision step attenuator such as a
To create this
signal level,
you must
use
an two
attenuator
inDC-1GHz
series with
the or
0 dBm
attenuator
AT1502W
DC-1GHz
ohm,
or
20 dB attenuators
PreciseRF50
step
attenuator
AT1502W
50such
ohm, as
two 20 dB
POWER
REF.
You
can
use
a
precision
step
attenuator
such
as
a
PreciseRF
step
attenuators
such
as
Tektronix
10X
(20dB)
50
ohm
2
W
011
0059-01.
Tektronix 10X (20dB) 50 ohm 2 W 011 0059-01.
attenuator AT1502W5)DC-1GHz
ohm,key
orwhen
two 20
attenuators
as signal to the
Press the 50
ENTER
youdB
have
connected such
-40 dBm
(d)
Press 10X
the ENTER
key
when
you
have
connected -40 dBm signal to the
FORWARD
input.
Tektronix
(20dB) 50
ohm
2W
011
0059-01.
FORWARD input.
6) The next display will prompt you to
(d) Press the ENTER key
when
you to
have
apply
-40 dBm
the connected -40 dBm signal to the
(e) The
next display
prompt youinput
to apply
-40
FORWARD
input.willREFLECTED
located
ondBm
the
panel
of DPM6000.
to the REFLECTEDrear
input
located
on the rear
(e) panel
The next
display will prompt you to apply -40 dBm
of DPM6000.
7) Press the ENTER key when you
to the REFLECTEDhave
inputconnected
located on
the rear
-40dBm
signal to
the REFLECTED
input.
(f) Press
theDPM6000.
ENTER key
when you have
connected -40 dBm signal to the
panel of
REFLECTED input.
(f) Press the ENTER key when you have connected -40 dBm signal to the
TheREFLECTED
next display will
prompt you to apply 0 dBm signal to the REFLECTED input
input.
located on the rear panel of DPM6000.
The next display will prompt you to apply 0 dBm signal to the REFLECTED input
(g)
Remove
therear
attenuation
from the REFLECTED
located
on the
panel of DPM6000.
input to restore the signal level to 0 dBm. Press
(g) Remove the attenuation from the REFLECTED
the ENTER key once you have applied the 0 dBm
input to restore the signal level to 0 dBm. Press
signal.
the ENTER key once you have applied the 0 dBm
signal.
DPM6000 Appnote V4 .pages
Page 37
(c) preciseRF 2013-2016
panel of DPM6000.
(f) Press the ENTER key when you have connected -40 dBm signal to the
p r e c i s e R F D P M 6 0 0 0 P O W E R M E T E R
REFLECTED input.
The next display will prompt you to apply 0 dBm signal to the REFLECTED input
located on the rear 8)
panel
DPM6000.
The of
next
display will prompt you to
apply 0 dBm signal to the
(g) Remove the attenuation
from the
REFLECTED
REFLECTED
input
located on the
panel.
input to restore therear
signal
level to 0 dBm. Press
the ENTER key9)once
you have
applied the
dBm
Remove
the attenuation
from0the
REFLECTED
input
to
restore
the
signal.
signal level to 0 dBm.
!U s e r ’ s
G u i d e
-
A p p l i c a t i o n
10) Press the ENTER key once you have applied the 0 dBm signal.
N o t e
11) The next display will prompt you
(i) The next display will to
prompt
0 dBm
apply 0you
dBmtotoapply
the FORWARD
inputlocated
located on
on the
to the FORWARD input
therear
rearpanel.
panel
the ENTER
key once
you
of the DPM6000. 12) Press
DPM6000
POWER
METER
have applied the 0 dBm signal.
This
completes
the Digital
to the 0
key
once
you have
applied
Analog converter slope calibration.
(j) Press the ENTER
the Digital to Analog converter slope calibration.
dBm signal. This completes
9. Calibrate the POWER REFERENCE
THE POWER REFERENCE is a precision signal source that delivers a 0 dBm
(1mW) 50 MHz pure sine wave with very low harmonic contents of -65 dB from the
fundamental signal. The POWER REFERENCE derives its stability and accuracy from
the use of a crystal oscillator and precision high frequency operational amplifier.
Harmonics are suppressed by a four pole Chebyshev filter, LC filter, and a single pole
narrow band adjustable bandpass filter. Calibration is performed by means of series
potentiometer.
(a) Locate the power reference circuit. It is housed in a shielded enclosure assuring
a low noise pure sine-wave.
(b) Open the POWER REFERENCE SHIELD. You will note two adjustments: C26
and R27. Make sure you have calibrated the power meter, spectrum analyzer or
oscilloscope you will be using for the power measurement. The most accurate
measurement is a laboratory quality power meter, then spectrum analyzer and
finally, an oscilloscope.
DPM6000 Appnote V4 .pages
Page 38
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
9. CALIBRATE THE POWER REFERENCE
The DP6000 POWER REFERENCE is a precision signal source that delivers
a 0 dBm (1mW) 50 MHz pure sine wave with very low harmonic contents of
-65 dB from the fundamental signal. The POWER REFERENCE derives its
stability and accuracy from the use of a crystal oscillator and precision high
frequency operational amplifier. Harmonics are suppressed by a four pole
Chebyshev filter, LC filter, and a single pole narrow band adjustable
bandpass filter. Calibration is performed by means of series potentiometer.
PROCEDURE
1) Locate the power reference circuit. It is housed in a shielded enclosure
assuring a low noise pure sine-wave.
2) Open the PWR REFERENCE shield. You will note two adjustments: C26
and R27. Make sure you have calibrated the power meter, spectrum
analyzer or oscilloscope you will be using for the power measurement. The
most accurate measurement is a laboratory quality power meter, then a
spectrum analyzer and finally, an oscilloscope.
3) Connect the PWR REFERENCE to a precision power meter such as an
HP436A Power Meter or HP 438A power peter using a calibrated and
known accuracy sensor such as an HP Power sensor 8484A power sensor
50 ohm .3nW - 10 uW and the appropriate 30 dB attenuator such as the 30
DB 50 OHM 90513 STODDARD fixed attenuator.
4) Peak the LC series tuned filter. Adjust C24 for maximum signal amplitude at
50 MHz.
5) Set the output level with R24 potentiometer to precisely 0 dBm. You may
need to adjust C24 slightly for optimum calibration.
6) If using an oscilloscope, adjust the peak to peak amplitude for 610 mV.
7) If your scope has FFT capability, you can check amplitude and harmonics
as well. Note the harmonic are 68.9 dB down.
s e r ’ samplitude
G u i d e - meets
A p p l i c a t i o n
8) If using a spectrum analyzer, check that!Usignal
specification.
N o t e
(a) If using a spectrum analyzer,
check thatthe
signalgreatest
amplitude
9) It takes some skill to achieve
meets specification.
accuracy. Re-check the measurement
with the covers installed. You may note
It takes
some skill to achieve
about a .02 dB difference
between
the greatest accuracy. Remeasurements since a slight power
check the measurement with
supply drift and stray RF
anYou may
the will
covershave
installed.
effect on the output. note about a .02 dB difference
Figure 6.10 Power Reference Spectrum Analyzer
between measurements since
a slight power supply drift and stray RF will have an effect on the ouput.
10. Updating the Firmware
DPM6000 Appnote V4 .pages
NOTE: THE FIRMWARE UPDATE CAN ONLY BE DONE BY PreciseRF AND OR
QUALIFIEDPage
SERVICE
SERVICE FACILITY.
39 PERSONNEL AT AN AUTHORIZED
(c) preciseRF
2013-2016
The DPM6000 functions are controlled by a PIC24fV32KA General Purpose, 16-Bit
Flash Microcontrollers with XLP Technology. To program the Microcontroller, you must
have a computer with the compiler installed and a PICkit(TM) 3 Programmer/Debugger
the covers installed. You may
Figure 6.10 Power Reference Spectrum Analyzer
note about a .02 dB difference
between measurements since
p r e c i s e R F D P M 6 0 0 0 P O W E R M E T E R
a slight power supply drift and stray RF will have an effect on the ouput.
10. Updating the Firmware
10. UPDATING THE FIRMWARE
NOTE: THE FIRMWARE UPDATE CAN ONLY BE DONE BY PreciseRF AND OR
QUALIFIED SERVICE PERSONNEL AT AN AUTHORIZED SERVICE FACILITY.
The
arecontrolled
controlled
a PIC24fV32KA
General
Purpose,
TheDPM6000
DPM6000 functions
functions are
by aby
PIC24fV32KA
General
Purpose,
16-Bit
16-Bit
Micro-controllers
with XLP Technology.
ToMicrocontroller,
program the you
microFlash Flash
Microcontrollers
with XLP Technology.
To program the
must
controller,
you
must
have
a
computer
with
the
compiler
installed
and
a
have a computer with the compiler installed and a PICkit(TM) 3 Programmer/Debugger
PICkit(TM) 3 Programmer/Debugger (programmer).
(programmer). See Figure 6.11
(a) Connect the programmer to the 6 pin programing port J6. Follow the compiler
PROCEDURE
instructions and program the Microcontroller.
r ’ s programming
G u i d e - A pport
p l i J6.
c a tFollow
i o n Nthe
o t
1) Connect the programmer to!U
thes6e pin
compiler instructions and
(b) Confirm
the firmware update by
program
the micro-controller.
e
turning the DPM6000 off and then
2) Confirm on
theagain.
firmware
update
See Figure
6.12.by
During
turning the
DPM6000
off and
the start
up messages,
the then
Figure 6.12 Firmware Version
on again.firmware
See Figure
6.12.displayed.
During
will be briefly
the start The
up first
messages,
the is the version number. The last six digits represent the
two Digits “V1”
firmwarefirmware
will bedate
briefly
displayed.
first2014.
two Digits “V1” is the version
“072014”
meaningThe
July 20,
number. The last six digits represent the firmware date “072014”
11. Replacing the Microcontroller
meaning July 20, 2014.
(a) If the Microcontroller must be replaced, it must be programmed before the
DPM6000 will operate properly. If you wish to replace it, call PreciseRF and order
a PIC24fV32KA
which has already been programmed with the latest firmware.
11. REPLACING
THE MICRO-CONTROLLER
(b) When callingmust
for customer
support, please
have
firmware version
handy. the
If the micro-controller
be replaced,
it must
bethe
programmed
before
PreciseRF
updates
the firmware
time to improve
DPM6000 will
operate
properly.
If you from
wishtime
to to
replace
it, call performance
PreciseRF and
and
correct bugs.
order a PIC24fV32KA which has already been programmed with the latest
firmware. When calling for customer support, please have the firmware
version handy. PreciseRF updates the firmware from time to time to improve
performance and correct DPM6000
bugs. POWER METER
DPM6000 Appnote V4 .pages
Page 40
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
X. R F P O W E R T E R M S
In this section, we review the power terms used in the DPM6000. While many
of these terms are derived mathematically and explained in this review, you
do not have to perform the calculations. They are computed by the on-board
computer contained in the DPM6000 and displayed in the HF-VHF
measurement pages. The information is provided as a convenience to give
you some insight and is readily available from a number of engineering text
books and the Internet.
1. VSWR
In telecommunications, standing wave ratio (SWR) is the ratio of the
amplitude of a partial standing wave at an antinode (maximum) to the
amplitude at an adjacent node (minimum), in an electrical transmission line.
The SWR is usually defined as a voltage ratio called the VSWR for voltage
standing wave ratio. For example, the VSWR value 1.2:1 denotes a maximum
standing wave amplitude that is 1.2 times greater than the minimum
standing wave value. It is also possible to define the SWR in terms of
current, resulting in the ISWR, which has the same numerical value. The
power standing wave ratio (PSWR) is defined as the square of the VSWR. To
avoid confusion, wherever SWR is used without modification in this article,
assume it is referring to the VSWR.
SWR is used as an efficiency measure for transmission lines, electrical
cables that conduct radio frequency signals, used for purposes such as
connecting ham radio transmitters and receivers with their antennas, and
distributing cable television signals. A problem with transmission lines is that
impedance mismatches in the cable tend to reflect the radio waves back
toward the source end of the cable, preventing all the power from reaching
the destination end. SWR measures the relative size of these reflections. An
ideal transmission line would have an SWR of 1:1, with all the power
reaching the destination and none of the power reflected back. An infinite
SWR represents complete reflection, with all the power reflected back down
the cable. The SWR of a transmission line can be measured with an
instrument called an SWR meter, and checking the SWR is a standard part
of installing and maintaining transmission lines.
Since power is proportional to V2, VSWR can be expressed in terms of
forward and reflected power as follows:
DPM6000 Appnote V4 .pages
Page 41
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
2. RETURN LOSS
In telecommunications, return loss is the loss of power in the signal returned/
reflected by a discontinuity in a transmission line or optical fiber. This
discontinuity can be a mismatch with the terminating load or with a device
inserted in the line. It is usually expressed as a ratio in decibels (dB);
where RL(dB) is the return loss in dB, Pi is the incident power and Pr is the
reflected power.
Return loss is related to both standing wave ratio (SWR) and reflection
coefficient (Γ). Increasing return loss corresponds to lower SWR. Return loss
is a measure of how well devices or lines are matched. A match is good if
the return loss is high. A high return loss is desirable and results in a lower
insertion loss. Return loss is used in modern practice in preference to SWR
because it has better resolution for small values of reflected wave.
Properly, loss quantities, when expressed in decibels, should be positive
numbers. However, return loss has historically been expressed as a
negative number, and this convention is still widely found in the literature.
The correct definition of return loss is the difference in dB between the
incident power sent towards the Device Under Test (DUT) and the power
reflected, resulting in a positive sign:
However, taking the ratio of reflected to incident power results in a negative
sign for return loss; where RL (dB) is the negative of RL(dB).
Return loss with a positive sign is identical to the magnitude of Γ when
expressed in decibels but of opposite sign. That is, return loss with a
negative sign is more properly called reflection coefficient. The S-parameter
S11 from two-port network theory is frequently also called return loss, but is
actually equal to Γ. Caution is required when discussing increasing or
decreasing return loss since these terms strictly have the opposite meaning
when return loss is defined as a negative quantity.
DPM6000 Appnote V4 .pages
Page 42
(c) preciseRF 2013-2016
!U s e r ’ s
G u i d e
-
A p p l i c a t i o n
N o t e
decreasing
p r eCaution
c i s is
e required
R F Dwhen
P Mdiscussing
6 0 0 0 increasing
P O W Eor R
M E T return
E R loss since these
terms strictly have the opposite meaning when return loss is defined as a negative quantity.
3. REFLECTION COEFFICIENT
2.InReflection
Coefficient the reflection coefficient is the ratio of the amplitude
telecommunications,
ofInthe
reflected wave tothe
thereflection
amplitude
of the is
incident
particular,
at a
telecommunications,
coefficient
the ratiowave.
of the In
amplitude
of the
discontinuity
a amplitude
transmission
line,
it is the
complex
ratio of
electric field
reflected
wave tointhe
of the
incident
wave.
In particular,
at athe
discontinuity
in a
strength of the reflected wave
transmission line, it is the complex ratio of the electric field strength of the reflected wave
(
(
) to that of the incident wave (
). This is typically represented with a
). This is typically represented with a (capital
(capital gamma) and can be written as:
) to that of the incident wave (
gamma) and can be written as:
The reflection coefficient may also be established using other field or circuit quantities.
The reflection coefficient may also be established using other field or circuit
The reflection coefficient of a load is determined by its impedance
and the impedance
quantities. The reflection coefficient of a load is determined by its
toward
the source and the impedance toward the source Zs
impedance
Simple circuit configuration showing measurement location of reflection
Simple circuit configuration showing measurement location of reflection coefficient.
coefficient.
Noticethat
that aa negative
negative reflection
coefficient
means
that the
wave receives
Notice
reflection
coefficient
means
thatreflected
the reflected
wave a
180°,
or , a
phase
receives
180°,shift.
or , phase shift. The absolute magnitude (designated by
vertical
bars)
of
the
reflection coefficient can be calculated from the standing
The absolute magnitude (designated by vertical bars) of the reflection coefficient can be
wave ratio,
calculated from the standing wave ratio,
:
: The reflection coefficient is displayed graphically using a Smith
chart.
The reflection coefficient is displayed graphically using a Smith chart.
DPM6000 POWER METER
4. MISMATCH LOSS
Mismatch loss in transmission line theory is the amount of power expressed
in decibels that will not be available on the output due to impedance
DPM6000 Appnote V4 .pages
Page 43
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
mismatches and signal reflections. A transmission line that is properly
terminated, that is, terminated with the same impedance as that of the
characteristic impedance of the transmission line, will have no reflections
and, therefore, no mismatch loss. Mismatch loss represents the amount of
power wasted in the system. It can also be thought of as the amount of
power gained if the system was perfectly matched. Impedance matching is
an important part of RF system design; however, in practice there will likely
be some degree of mismatch loss. In real systems, relatively little loss is due
to mismatch loss and is often on the order of 1dB. Mismatch loss (ML) is the
ratio of incident power to the difference between incident and reflected
power.
Above is a simple circuit showing characteristic impedance Zo and the load
impedance ZL. In a perfectly matched system ZL=Zo. There is no mismatch
loss.
where
The fraction of incident power delivered to the load is
Above, is a simple circuit showing incident power, Pi, on a load. The
reflected power will be the difference between Pi and the power delivered,
Pd.
DPM6000 Appnote V4 .pages
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(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
where is the magnitude of the reflection coefficient. Note that as the
reflection coefficient approaches zero, power to the load is maximized.
If the reflection coefficient is known, mismatch can be calculated by
In terms of the voltage standing wave ratio (VSWR):
5. dBm
dBm (sometimes dBmW or Decibel-milliwatts) is an abbreviation for the
power ratio in decibels (dB) of the measured power referenced to one
milliwatt (mW). It is used in radio, microwave and fiber optic networks as a
convenient measure of absolute power because of its capability to express
both very large and very small values in a short form. Compare dBW, which
is referenced to one watt (1000 mW). Since it is referenced to the watt, it is
an absolute unit, used when measuring absolute power. By comparison, the
decibel (dB) is a dimensionless unit, used for quantifying the ratio between
two values, such as signal-to-noise ratio.
In audio and telephony, dBm is typically referenced relative to a 600 ohm
impedance, while in radio frequency work dBm is typically referenced
relative to a 50 ohm impedance. A power level of 0 dBm corresponds to a
power of 1 milliwatt. A 3 dB increase in level is approximately equivalent to
doubling the power, which means that a level of 3 dBm corresponds roughly
to a power of 2 mW. For each 3 dB decrease in level, the power is reduced
by about one half, making −3 dBm correspond to a power of about 0.5 mW.
To express an arbitrary power P in watts as x in dBm, or vice versa, the
following equivalent expressions may be used:
DPM6000 Appnote V4 .pages
Page 45
(c) preciseRF 2013-2016
reduced by about one half, making −3 dBm correspond to a power of about 0.5 mW.
To express an arbitrary power P in watts as x in dBm, or vice versa, the following
equivalent expressions may be used:
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
and
and
where P is the power in W and x is the power level in dBm. Below is a table
where P is the power in W and x is the power level in dBm. Below is a table summarizing
summarizing useful cases:
useful cases:
Power level Power
Notes
80 dBm
100 kW
Typical transmission power of FM radio station with 50kilometer (31 mi) range
62 dBm
1.588 kW = 1,588
W
1500 W is the maximum legal power output of a U.S. ham
radio station.
60 dBm
1 kW = 1,000 W
Typical combined radiated RF power of microwave oven elements
50 dBm
100 W
Typical thermal radiation emitted by a human body
Typical maximum output RF power from a ham radio HF
transceiver
40 dBm
10 W
Typical PLC (Power Line Carrier) transmit power
37 dBm
5W
Typical maximum output RF power from a handheld ham radio VHF/UHF transceiver
36 dBm
4W
Typical maximum output power for a Citizens' band radio station (27 MHz) in many countries
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
Page 46
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
!U s e r ’ s
G u i d e
M E T E R
-
A p p l i c a t i o n
N o t e
33 dBm
2W
Maximum output from a UMTS/3G mobile phone (Power
class 1 mobiles) Maximum output from a GSM850/900 mobile phone
30 dBm
1 W = 1,000 mW
Typical RF leakage from a microwave oven[citation needed]
DCS or GSM 1,800/1,900 MHz mobile phone. EIRP IEEE
802.11a (20 MHz-wide channels) in either 5 GHz Sub-band 2
(5,470–5,725 MHz) provided that transmitters are also IEEE
802.11h-compliant, or U-NII-3 (5,725–5,825 MHz). The former is EU only, the latter is US only.
27 dBm
500 mW
Typical cellular phone transmission power
Maximum output from a UMTS/3G mobile phone (Power
class 2 mobiles)
24 dBm
251 mW
Maximum output from a UMTS/3G mobile phone (Power
class 3 mobiles). 1,880–1,900 MHz DECT (250 mW per
1,728 kHz channel). EIRP for Wireless LAN IEEE 802.11a
(20 MHz-wide channels) in either the 5 GHz Sub-band 1
(5,180–5,320 MHz) or U-NII-2 & -W ranges (5,250–
5,350 MHz & 5,470–5,725 MHz respectively). The former is
EU only, the latter is US only.
23 dBm
200 mW
EIRP for IEEE 802.11n Wireless LAN 40 MHz-wide (5 mW/
MHz) channels in 5 GHz sub-band 4 (5,735–5,835 MHz, US
only) or 5 GHz sub-band 2 (5,470–5,725 MHz, EU only). Also
applies to 20 MHz-wide (10 mW/MHz) IEEE 802.11a Wireless
LAN in 5 GHz Sub-band 1 (5,180–5,320 MHz) if also IEEE
802.11h compliant (otherwise only 3 mW/MHz → 60 mW
when unable to dynamically adjust transmission power, and
only 1.5 mW/MHz → 30 mW when a transmitter also cannot
dynamically select frequency).
21 dBm
125 mW
Maximum output from a UMTS/3G mobile phone (Power
class 4 mobiles)
20 dBm
100 mW
EIRP for IEEE 802.11b/g Wireless LAN 20 MHz-wide channels in the 2.4 GHz ISM band (5 mW/MHz). Bluetooth Class
1 radio. Maximum output power from unlicensed AM transmitter per U.S. Federal Communications Commission (FCC)
rules 15.219.
15 dBm
32 mW
Typical Wireless LAN transmission power in laptops.
7 dBm
5.0 mW
Common power level required to test the Automatic Gain
Control circuitry in an AM receiver.
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
Page 47
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
!U s e r ’ s
G u i d e
M E T E R
-
A p p l i c a t i o n
N o t e
4 dBm
2.5 mW
Bluetooth Class 2 radio, 10 m range
3 dBm
2.0 mW
More precisely (to 8 decimal places) 1.9952623 mW
0 dBm
1.0 mW =
1,000 µW
Bluetooth standard (Class 3) radio, 1 m range
−10 dBm
100 µW
Typical maximum received signal power (−10 to −30 dBm) of
wireless network
−30 dBm
1.0 µW = 1,000 nW
−60 dBm
1.0 nW = 1,000
pW
The Earth receives one nanowatt per square meter from a
magnitude +3.5 star
−73 dBm
50.12 pW
"S9" signal strength, a strong signal, on the S-meter of a typical ham or shortwave radio receiver
−80 dBm
10 pW
Typical range (−70 to −90 dBm) of wireless received signal
power over a network (802.11 variants)
−100 dBm
0.1 pW
−111 dBm
0.008 pW = 8 fW
Thermal noise floor for commercial GPS single channel signal bandwidth (2 MHz)
−127.5
dBm
0.178 fW = 178
aW
Typical received signal power from a GPS satellite
−174 dBm
0.004 aW = 4 zW
Thermal noise floor for 1 Hz bandwidth at room temperature
(20 °C)
−192.5
dBm
0.056 zW = 56 yW Thermal noise floor for 1 Hz bandwidth in outer space (4
kelvins)
−∞ dBm
0W
Zero power is not well-expressed in dBm (value is negative
infinity)
The signal intensity (power per unit area) can be converted to received signal power by
multiplying by the square of the wavelength and dividing by 4π
The In
signal
(power of
per
unit area)
can
be converted
to received
Unitedintensity
States Department
Defense
practice,
unweighted
measurement
is normally
signal
power
by multiplying
the square
thebe
wavelength
and In
dividing
understood,
applicable
to a certainby
bandwidth,
whichofmust
stated or implied.
audio, 0 by
4π
. often corresponds to approximately 0.775 Volts, since 0.775 Volts dissipates 1 mW in a
dBm
Ω load.States
dBu measures
against of
thisDefense
referencepractice,
voltage without
the 600 Ω restriction.
In600
United
Department
unweighted
measurement
Conversely,
for
RF
situations
with
a
50
Ω
load,
0
dBm
corresponds
to
approximately
0.224
is normally understood, applicable to a certain bandwidth, which must
be
Volts
since
0.224
Volts
dissipates
1
mW
in
a
50
Ω
load.
The
dBm
is
not
a
part
of
the
stated or implied. In audio, 0 dBm often corresponds to approximately 0.775
International
of Units
and therefore
is discouraged
use indBu
documents
or
volts,
since System
0.775 volts
dissipates
1 mW
in a 600from
Ω load.
measures
systems this
that adhere
to SI units
(the corresponding
SI unit
the watt). However
the straight
against
reference
voltage
without the 600
Ωisrestriction.
Conversely,
for
decibel
(dB),
being
a
unit-less
ratio
of
two
numbers,
is
perfectly
acceptable.
RF situations with a 50 Ω load, 0 dBm corresponds to approximately 0.224
volts since 0.224 volts dissipates 1 mW in a 50 Ω load. The dBm is not a part
of the International System of Units and, therefore, is discouraged from use
in documents or systems that
adhere
to SI
units (the corresponding SI unit is
DPM6000
POWER
METER
the watt). However, the straight decibel (dB), being a unit-less ratio of two
numbers, is perfectly acceptable. Expression in dBm is typically used for
optical and electrical power measurements, not for other types of power
(such as thermal).
DPM6000 Appnote V4 .pages
Page 48
(c) preciseRF 2013-2016
p r e c i s e R F
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P O W E R
M E T E R
6. TRANSMISSION LINE
In communications and electronic engineering, a transmission line is a
specialized cable or other structure designed to carry alternating current of
radio frequency, that is, currents with a frequency high enough that their
wave nature must be taken into account. Transmission lines are used for
purposes such as connecting radio transmitters and receivers with their
antennas, distributing cable television signals, trunklines routing calls
between telephone switching centers, computer network connections, and
high speed computer data buses.
This discussion covers a two-conductor transmission line, such as parallel
line (ladder line), coaxial cable, strip-line and micro-strip. Ordinary electrical
cables suffice to carry low frequency alternating current (AC), such as mains
power, which reverses direction 100 to 120 times per second, and audio
signals. However, they cannot be used to carry currents in the radio
frequency range or higher, which reverse direction millions to billions of
times per second, because the energy tends to radiate off the cable as radio
waves, causing power losses.
Radio frequency currents also tend to reflect from discontinuities in the cable
such as connectors and joints, and travel back down the cable toward the
source.These reflections act as bottlenecks, preventing the signal power
from reaching the destination. Transmission lines use specialized
construction, and impedance matching, to carry electromagnetic signals
with minimal reflections and power losses. The distinguishing feature of most
transmission lines is that they have uniform cross sectional dimensions along
their length, giving them a uniform impedance, called the characteristic
impedance, to prevent reflections. Types of transmission line include parallel
line (ladder line, twisted pair), coaxial cable, strip-line and micro-strip. The
higher the frequency of electromagnetic waves moving through a given
cable or medium, the shorter the wavelength of the waves. Transmission
lines become necessary when the length of the cable is longer than a
significant fraction of the transmitted frequency's wavelength.
At microwave frequencies and above, power losses in transmission lines
become excessive, and waveguides are used instead, which function as
"pipes" to confine and guide the electromagnetic waves. Some sources
define waveguides as a type of transmission line; however, this discussion
will not include them. At even higher frequencies, in the terahertz infrared
and light range, waveguides in turn become lossy, and optical methods,
(such as lenses and mirrors), are used to guide electromagnetic waves.
Below is a representation of the four terminal model:
DPM6000 Appnote V4 .pages
Page 49
(c) preciseRF 2013-2016
Below is a representation of the four terminal model
infrared and light range, waveguides in turn become lossy, and optical methods, (such as
lenses and mirrors), are used to guide electromagnetic waves.
p r e c of
i sthee four
R Fterminal
D P model
M 6 0 0 0
Below is a representation
P O W E R
M E T E R
6. Variations on the schematic electronic symbol for a transmission line.
Variations
on the schematic
electronic
symbol
foras
a transmission
line is
For the purposes of analysis,
an electrical
transmission
line can be
modeled
a twoshown below.
For the
purposes
of analysis,line.
an electrical transmission line
6.
Variations
on
the
schematic
electronic
symbol
for
a
transmission
port network (also called a quadrupole network), as follows:
be modeled
astransmission
a two-port line
network
called
quadrupole network).
For the purposes of can
analysis,
an electrical
can be(also
modeled
as aatwoport network (also called a quadrupole network), as follows:
In the simplest case, the network is assumed to be linear (i.e. the complex
voltage
across
either port
proportional
to the complex
In the simplest case, the
network
is assumed
to beis
linear
(i.e. the complex
voltage current flowing into
it whentothere
are no reflections),
and
two there
portsare
areno
assumed to be
across either port is proportional
the complex
current flowing
intothe
it when
In the simplest case,interchangeable.
the network is assumed
be linear (i.e. the
voltage
If thetotransmission
linecomplex
is uniform
along its length, then its
reflections), and the two ports are assumed to be interchangeable. If the transmission line is
across either port is proportional
complex
current flowing
it when
there arecalled
no
behaviortoisthe
largely
described
by a into
single
parameter
the characteristic
uniform along its length, then its behavior is largely described by a single parameter called
reflections), and the twoimpedance,
ports are assumed
to be
interchangeable.
If the
linevoltage
is
symbol
Z0.
This is the ratio
of transmission
the complex
of a given
theuniform
characteristic
impedance,
symbol
Z0.
This
is
the
ratio
of
the
complex
voltage
of
a
given
along its length,wave
then its
is largely
described
by same
a singlewave
parameter
called
tobehavior
the complex
current
of the
at any
point on the line.
wave
to
the
complex
current
of
the
same
wave
at
any
point
on
the
line.
Typical
values
of Z0
Typical
values
of
Z0
coaxial
100
the characteristic impedance,
symbol
Z0.
This
the
ratio
given
!U
s iseare
r ’ 50
s or
Gof75
uthe
i ohms
dcomplex
e for
- voltage
Aa p
p lofi a
c cable,
a t i o about
n N o
t eohms
for
a
twisted
pair
of
wires,
and
about
300
ohms
for
a
common
type
of
arewave
50 orto75
ohms
for
a
coaxial
cable,
about
100
ohms
for
a
twisted
pair
of
wires,
and
about
the complex current of the same wave at any point on the line. Typical values of Z0
untwisted
pair
used
inohms
radio
transmission.
300
ohms
common
of untwisted
pair100
used
in radio
transmission.
are 50 orfor
75aohms
for atype
coaxial
cable,
about
for
a twisted
pair of wires, and about
When sending power down a transmission line, it is usually desirable that as much
300 ohms for a commonWhen
type ofsending
untwistedpower
pair used
in radio
transmission.line, it is usually desirable that as
down
a transmission
power as possible willmuch
be absorbed
bypossible
the load will
andbe
asabsorbed
little as possible
reflected
power as
by the will
loadbeand
as littleback
as
will be
back
toimpedance
the source.equal
This can
beinensured
to the source. This canpossible
be ensured
by reflected
making the
load
to Z0,
which by
DPM6000
POWER
METER
the load
case the transmissionmaking
line is said
to beimpedance
matched. equal to Z0, in which case the transmission line
POWER METER
is said DPM6000
to be matched.
A transmission line is drawn as two black wires. At a distance x into the line, there is
current I(x) traveling through each wire, and there is a voltage difference V(x) between the
wires. If the current and voltage come from a single wave (with no reflection), then
DPM6000 Appnote V4 .pages
Page 50
V(x) / I(x) = Z0, where Z0 is the characteristic impedance of the line.
(c) preciseRF 2013-2016
Some of the power that is fed into a transmission line is lost because of its resistance.
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
A transmission line is drawn as two black wires. At a distance x into the line,
there is current I(x) traveling through each wire, and there is a voltage
difference V(x) between the wires. If the current and voltage come from a
single wave (with no reflection), then V(x) / I(x) = Z0, where Z0 is the
characteristic impedance of the line.
Some of the power that is fed into a transmission line is lost because of its
resistance. This effect is called ohmic or resistive loss. At high frequencies,
another effect called dielectric loss becomes significant, adding to the
losses caused by resistance. Dielectric loss is caused when the insulating
material inside the transmission line absorbs energy from the alternating
electric field and converts it to heat. The transmission line is modeled with a
resistance (R) and inductance (L) in series with a capacitance (C) and
conductance (G) in parallel. The resistance and conductance contribute to
the loss in a transmission line.
The total loss of power in a transmission line is often specified in decibels
per meter (dB/ m), and usually depends on the frequency of the signal. The
manufacturer often supplies a chart showing the loss in dB/m at a range of
frequencies. A loss of 3 dB corresponds approximately to a halving of the
power. High-frequency transmission lines can be defined as those
designed to carry electromagnetic waves whose wavelengths are shorter
than or comparable to the length of the line. Under these conditions, the
approximations useful for calculations at lower frequencies are no longer
accurate. This often occurs with radio, microwave and optical signals, metal
mesh optical filters, and with the signals found in high-speed digital circuits.
DPM6000 Appnote V4 .pages
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p r e c i s e R F
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XI. S P E C I F I C A T I O N S
P O W E R
!U s e r ’ s
M E T E R
G u i d e
-
A p p l i c a t i o n
N o t e
VIII. Specifications:
Item
DDS-1 Coupler
-30dB
DDS 2KW Coupler
-45dB
MWSD6 MS
Sensor
Direct Input
Frequency
Range
2-100 MHz
1.8 MHz - 54 MHz
2 MHz - 6 GHz
Power Range
-20 dBm (.01mW)
+50 dBm (100 W)
-5 dBm (32mW)
+63 dBm (2000W)
-20 dBm (10 uW)
- 60 dBm (.001 uW)
+20 dBm (100 mW) +20 dBM (100mW)
2 (Fwd & Ref)
1 Sensor Input
2-500 MHz
Number of
Channels
2 (Fwd & Ref)
2 (Fwd & Ref)
Calibration
Source
Precision crystal oscillator with operational amplifier shaped sine-wave. Frequency
32.000 MHz, 0 dBm (1mW) into 50 ohms. Spurious signals -60 dB, Short term stability (40 hours) .05dB, long term stability 12 month (.5 dBM)
Uncertainty at
22 deg. C +/- 4
deg. C,
Calibrator: 0 dBm +/- .055 dB (1.27%) when calibrated with NIST traceable
methods.
Counter
Direct forward input: 1KHz to 55 MHz, 8 digit TCXO 1PPM, 10 dBm
For sensor, noise, high-frequency calibration uncertainty, consult power sensor
specifications.
Counter: 1KHz to 100 MHz, 8 digit TCXO 1PPM, 1 dBm
(Display max 99.999,999 Hz )
Input/Output
Front panel: Counter In, Sensor In, POWER REF, Rear: Clock IN/OUT, FWD, REFL,
Internal/External switch +9VDC
Measurements
Fwd/Ref Watts/dBm, SWR, Peak/Avg, RL, RC(p), Mismatch,%, Power, Direct
Freq, Counter Freq
Table 8.1 DPM6000 Specifications
All products are calibrated and tested to meet or exceed published specifications. The
All products are calibrated and tested to meet or exceed published
optional NIST calibration certificate is provided for users needing a calibration reference
specifications.
The optional NIST calibration certificate is provided for
showing the actual performance achieved. Calibration done using NIST traceable
users
needing a calibration reference showing the actual performance
instruments. Some test and measurement equipment was calibrated using NIST traceable
achieved.
Calibration is done using NIST traceable instruments. Some
instruments. The item calibrated may be used as a calibration reference only, and shall not
testbeand
equipment
was
calibrated
using
NIST traceable
usedmeasurement
as a NIST calibration
standard. This
certificate
shall not
be reproduced
without the
instruments.
The
item calibrated
may be
used
asneed
a calibration
reference
express written
permission
from the calibration
facility.
If you
support or service
for
only,
and
shall
not
be
used
as
a
NIST
calibration
standard.
This
your PreciseRF product, whether the product is under warranty or otherwise, please contact
certificate
not beforreproduced
without
the express written
PreciseRFshall
and arrange
a return or repair
authorization.
permission from the calibration facility. If you need support or service for
your PreciseRF product, whether the product is under warranty or
DPM6000 POWER
otherwise, please contact PreciseRF
andMETER
arrange for a return or repair
authorization. Specifications subject to change without notice (c) 2016
preciseRF.
DPM6000 Appnote V4 .pages
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XII. P O W E R M E A S U R E M E N T S F U N D A M E N T A L S
Accurate power measurements are essential to the operation of many RF/
microwave-based systems found in the communications industry and ham
radio environment. For example, checking transmitted power from an
antenna, ensures that a communications system remains within its power
limits. The methods of measuring power in RF/microwave systems have
improved over the last several decades. To better appreciate today’s powermeasurement solutions, it may help to review the fundamentals of RF/
microwave power measurements.
13. RF POWER SENSORS TYPES
In the laboratory, the accepted means of measuring the power levels of
high-frequency signals is to use a power meter and the appropriate power
sensor. There are four types of power sensors: the thermistor, thermocouple,
inductive coupled and diode-based sensors. All four sensor types are
appropriate for measuring the power levels of continuous-wave (CW)
signals, but only diode and inductive sensors have the fast response times
to accurately measure the time-varying power of pulsed and modulated
signals.
14. THERMISTOR SENSOR
Writes Jack Brown in his discussion in a Microwave&RF article: “Power
sensors based on thermistors gauge the level of power from rises in
temperature due to the heating effects of applied power on resistors”.
Thermistors are semiconductors with a negative temperature coefficient.
They are a type of bolometer, a device in which resistance changes with
temperature changes caused by applied RF/microwave power.
Because thermistors exhibit nonlinear resistance characteristics as a
function of applied power, using them for power measurements is anything
but straightforward. They are typically used with a bridge and some form of
bias (AC or DC) to maintain a thermistor assembly or mount at a constant
resistance with applied RF/microwave power. A power meter tuned to the
sensor’s changes in bias energy as a function of applied power is then used
to calculate the RF/microwave power over a dynamic range enabled by the
thermistor mount and its supporting electronics, including video amplifiers.
15. THERMOCOUPLE SENSOR
Thermocouple-based power sensors work on the principle that some
dissimilar metals will produce a voltage due to temperature differences at
the junctions of two of the metals. Known as the Peltier effect—named for
DPM6000 Appnote V4 .pages
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French physicist Jean- Charles Peltier, who discovered the phenomenon in
1834—a thermocouple formed of two appropriate metals can generate a
!U s e r ’ s
small voltage in response to temperature rises.
When current flows through a junction of a thermocouple formed of two of
4. Diode rise
Sensor
the proper metals, it induces a temperature
in one of the metals in the
junction, with heat absorbed by the other
metal in the
junction.
Themake
resulting
Diode-based
power
sensors
flow of electrons or charge can be used as part of a power sensor. A poweruse of a Schottky diode’s capability of
sensor thermocouple is usually a loop or circuit made of two different metals,
or converting
alternating
with two junctions. Heat is appliedrectification,
to one junction
but not theanother,
with
resulting electron flow towards thecurrent
cold junction.
Modern
power sensors
(AC) flowing
alternately
in two dibased on thermocouple technology generally use thermocouples fabricated
rections to a direct current (DC) signal
as semiconductor chips with the appropriate metal junctions.
flowing in only one direction. These sen-
16. DIODE SENSOR
sor operate in the square law region.
G u i d e
For a
detector
its incide
"linear" o
voltage
square-r
Thus
power's
Diode-based power sensors make use
of a Schottky
diode’sdocapability
of
Diode-based
sensors
not measure
rectification, or converting an alternating
(AC)
the heatcurrent
content
of aflowing
signal, alternately
but insteadin
two directions to a direct current (DC) signal flowing in only one direction.
rectify the signal, converting high freThese sensors operate in the square law region. Diode-based sensors do
energy
to DC
by means
of the
not measure the heat content of a quency
signal, but
instead
rectify
the signal,
non-linear
characconverting high frequency energydiode’s
to DC by
means ofcurrent-voltage
the diode’s non-linear
current-voltage characteristics. teristics.
squared
In the square law region, the
diode’s detected output
voltage is proportional to the
input power, and power can
be measured directly. The
square law region extends
from approximately –60 dBm
to –10 dBm, giving a
dynamic range of 50 dB.
Above –10 dBm, the square
law no longer applies and
correction factors must be
applied to ensure accurate
power measurements.
and mic
vices to
vices, th
pabilities
porting p
Ther
sensor w
attenuat
measure
cost upw
measure
Figure 9.2 MWSD6 6GHz Sensor
In the square law region, the diode’s
detected
outputoutput
voltage
is proportional
to
For a certain range of power levels,
a detector's
voltage
is
proportional to its incident power measure
watts.and
In "linear"
operation,
the input in
power,
power can
be measOhm's law says that voltage should
be
proportional
to
the
square
root exof
ured directly. The square law region
power. Thus, in the square law region, power's relationship to voltage has
tends from approximately –60 dBm to –10
been squared. As diodes were fabricated on different materials, from early
dBm, giving
dynamic the
range
of 50 dB.and
silicon devices to later gallium arsenide
(GaAs)a devices,
bandwidth
frequency capabilities of the devices
increased,
supporting
power
Above
–10 dBm,
the square
law no
measurements through RF and microwave frequencies.
longer applies and correction factors must
be applied to ensure accurate power
DPM6000 Appnote V4 .pages
different
Page 54
measurements.
(c) preciseRF 2013-2016
!U s e r ’ s
p r e c i s e R F
D P M 6 0 0 0
P O W E R
G u
M E T E R
5. In-line Sensor (Coupler)
Thermistor, Thermocouple and Diode sensor will require wide-band high
An in-line
sensor with These
50-75 Ω
power attenuators for high RF power transmitter
measurements.
impedance
accurately
attenuators can cost upward of $2,000 characteristic
for power making
measurements
of
100W -1 KW.
measure RF power dissipated in a
matched or unmatched load. The design
17. DPM6000 POWER METER COUPLERS
is a wide-band, directional coupler/
And in-line sensor (Coupler) has a 50-75 Ω characteristic impedance to
current-voltage sensor suitable for
accurately measure RF power dissipated in a matched or unmatched load.
and harmonic
power
The design is a wide-band, directional fundamental
coupler/ current-voltage
sensor
suitable for fundamental and harmonic measurements.
power measurements. A comparison
with a standard watt meter using dummy load impedances shows that in-line
A comparison
with a standard
sensors are as accurate in mismatched conditions
as thermistor
or diode
wattmeter
using
dummy
load
impedances
sensors.
The in-line sensor, often called a
coupler or sampler, may consist of
a transformer or directional coupler
which samples RF signals at a
specific attenuation and frequency
range. These directional couplers
are used when both forward and
reflected power must be measured
as in measuring VSWR. These
couplers measure the forward or
reflected power in a transmission
line. Generally, the transmission line
is terminated in a load. This load
can be an antenna, fixed
termination or an attenuator,
typically 50 -75 Ω, depending on
the application.
cou
tran
sam
atte
dire
forw
me
cou
pow
the
loa
term
-75
is t
wh
pow
me
atte
and
tran
con
cor
Figure 9.3 In-line Sensor Types
The advantage of this type of
sensor is that unlike thermistor or
diode sensors which require an attenuator
for that
higher
power
measurements,
shows
in-line
sensors
are as
power can be measured at very high levels
sinceinthe
attenuation
factor is as
accurate
mismatched
conditions
part of the sensor and ranges from 20 to 40 dB. Since these sensors employ
thermistor or diode sensors.
a transformer,usually a toroid, consideration must be given to potential core
saturation. These sensors have a frequency range from 2MHz to upward of 1
GHz (low power). They generally cost less than the other sensor types. The
disadvantage is their lower power measurement accuracy and linearity.
freq
1G
les
dis
me
18. RF POWER
Power is energy over a given time, defined in values of wattage, with 1 watt
(W) equal to 1 joule (J) per second. One volt (V) is equal to 1W per ampere
DPM6000 POWER MET
DPM6000 Appnote V4 .pages
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(A), or 1 V = 1 W/A. Power is the product of voltage and current, or P = V × I,
although this value tends to vary in most systems over time. Because power
can change so much for some signals (such as digitally modulated signals),
measuring RF/ microwave signal power requires test equipment made for a
specific type of signal.
19. POWER OVER TIME
All power measurements occur over some finite time. So, in the strictest
sense, power measurements are always instantaneous. Power is often
defined as peak power, carrier power, average power, Peak Envelope Power
(PEP) and sometimes, incorrectly, as RMS power. In the United States, the
Federal Communications Commission uses PEP to set maximum power
limits for amateur radio transmitters. The maximum power allowed on certain
frequencies using SSB modulation is 1,500 Watts PEP. PEP is the average
power supplied by the transmitter/linear RF amplifier to the transmission line
and eventually the antenna, during one radio frequency cycle at the crest of
the modulation envelope, under normal operating conditions.
20. WHAT IS ELECTRIC POWER
Electric power is the rate at which electric energy is transferred by an
electric circuit. The unit of power is the watt. Joule heating, is ohmic heating
and resistive heating. It is the process by which the passage of an electric
current through a conductor releases heat. It was initially studied by James
Prescott Joule in 1841.There is potential power (no heating), instantaneous
power and average power. When one volt is applied across a one ohm
resistor, one ampere of current flows though the resistor. Since P=IE then the
resistor is dissipating one watt. When power is defined over time, it is
expressed in joules. One joule equals one watt per second; that is
synonymous to one watt second. When power is referred to as
“instantaneous power”, it is expressed as a fraction of a joule; for example, if
the instant of that power lasts for one millisecond, that equals one milli-joule
or one milliwatt second.
It should be noted that the power applied to an ideal antenna does not heat
the antenna. The antenna radiates the power (less any losses, which indeed
heats the antenna). This radiated power is eventually absorbed by the
atmosphere, natural and manmade objects, and also at the radio receiver’s
antenna and receiving circuits; eventually the energy is transformed either to
useful work, or heat.
21. PEP POWER VERSUS CW POWER
PEP may be more difficult to measure than CW power. Nonetheless, PEP is
the average power during one radio frequency cycle at the crest of the
DPM6000 Appnote V4 .pages
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modulation envelope and continuous wave (CW) power is also an average
power, thus they are equal. All power measurements rely on these formulas:
For DC power measurements, use: P= E2/R. For AC, PEP measurements,
use: P= (Eavg)2/R Peak.
22. PEAK POWER
Measuring peak voltage with an oscilloscope is not difficult, and generally,
the load impedance (R) in amateur radio transmitters and transmission lines
equals 50 ohms (sometimes 300 ohms). Making a peak power measurement
is straightforward by measuring the peak voltage. Some users find it simpler
to measure the peak-peak voltage. In that case, divide the results by 2 to get
peak voltage. See Figure 10.1. Note, the Max (peak) voltage is 70 volts,
which is half of the Pk-Pk voltage. To solve for peak power, square the peak
voltage (E) and divide by 50 (the load impedance) So: (70) =4900/50=98
watts peak.
23. AVERAGE POWER
Let’s dispel the myth of RMS power. There is no such thing as RMS power.
RMS is an abbreviation of Root Mean Squared. The term “Mean” is just
another word for average. With respect to power calculations, the AC RMS
voltage is the equivalent to the DC voltage. For example, 25V RMS or 25V
DC across a non-inductive 50ohm load results in identical power dissipation
of 12.5 watts in either case.
The RMS value by itself is not the comparable heating power and it doesn’t
correspond to any useful physical quantity; no heat, no power. Recall P=IE,
and I=E/R. Voltage (E), nor current (I) by themselves generate power. The
power is only produced when a current is induced by a voltage across a
load R. Finally, RMS and average values of nearly all waveforms are
different. One exception is a steady DC waveform, for which the average,
RMS, and peak values are identical.
Thus, substitution volts for f we arrive at the familiar equation below:
Fortunately, this mathematical integration can be reduced to the RMS
values. And for an ideal sine wave that happens to be the peak waveform
DPM6000 Appnote V4 .pages
Page 57
(c) preciseRF 2013-2016
tion envelope and continuous wave (CW)
power is also an average power, thus
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
rely on these formulas: For DC power
measurements, use:
value multiplied by .707. So, power is still power, whether PEP or average.
The correct way to express average AC P=
power
E2/Ris Pavg. as a result:
Pavg=(ERMS) /R . We know that oscilloscopes are great tools to measure
AC,
PEP multiplying
measurements,
voltages of AC wave-forms. For a perfectFor
sine
wave,
peakuse:
voltage times .707 will give us RMS voltage. Some of the newer scopes
P= (Eavg)2/R Peak
make this step easy and calculate the RMS voltage directly. These
calculations are quite accurate even for Peak
non-sinusoidal
waveforms.
Power
See Figure 10.1. What is the
average power if the peak voltage
is 70 volts?
transmitters and transmission lines
equals 50 ohms (sometimes 300 ohms).
Making a peak power measurement is
There
RMS
Squar
word
calcul
induct
power
case.
Th
comp
corres
tity; no
I=E/R
thems
only p
by a v
RMS
wavef
a stea
DPM6000 POWER METER
Figure 10.2 Sampled Waveform
24. DPM6000 POWER
METER CALCULATIONS
Calculate the RMS voltage (70 x .707 = 49.5 volts). You’ll note that in Figure
10.1 the calculated RMS voltage is 50 volts not 49.5 volts. That is because
the oscilloscope measurement was done on a somewhat imperfect sine
wave, thus giving a slightly higher reading.
Square the voltage, and divide by 50 (the load impedance):
Page 58
7. Le
ple, 2
load impedance (R) in amateur radio
DPM6000 Appnote V4 .pages
6. Av
equiva
See Figure 10.2. If one were to
sample a waveform at regularly
spaced times, and then add up
their values and divide that total
by the number of samples taken,
one would have approximately the
average value of whatever the
waveform represents; this could
be voltage, current or power. The
Figure 10.1 Power Waveform
less the time intervals between
Measuring peak voltage with an oscilsamples, the more accurate the
average will be.
loscope is not difficult, and generally, the
The mathematical integration
is a method to find what the
value would be if we could
minimize the time interval
really close to zero. That’s
important if we want to
calculate the exact average
value of some waveforms.
The corresponding formula
for a continuous function (or
waveform) f(t) defined over
the interval dV/dT.
(
they are equal. All power measurements
(c) preciseRF 2013-2016
!U s e r ’ s
p r e c i s e R F
D P M 6 0 0 0
Step one: Calculate the RMS voltage
G u i d e
-
P O W E R
A p p l i c a t i o n
N o t e
M E T E R
See figure 10.3. The crest of the
(70 x .707 = 49.5 volts). You’ll note that in
modulation envelope is the peak value;
(49.5)=2450/50=49 watts Avg.
Figure 1, the calculated RMS voltage is
this oscilloscope labels it as “Max”. It is
A
common
error
some
make
calculating
power
they
multiply
PEP
50 volts not 49.5 volts. That is because
197 average
volts. Note,
that isthe
scope
calculated
by .707, i.e. 98 watts times .707. This results in an incorrect answer of 69.3
the oscilloscope measurement was done
the RMS voltage as 86.6 volts which
watts. Power is always calculated by squaring the voltage and dividing the
on a somewhat
imperfect
thus
would be correct for a steady RF carrier.
result
by thesine
loadwave,
impedance.
giving a slightly higher reading.
However, here the modulation is not a
steady carrier, but instead represents the
25. Square
PEP POWER
Step two:
the voltage, and
The International Telecommunicationminimum
Union (ITU)
Regulations
define
andRadio
maximum
modulation
levdivide by 50 (the load impedance):
the terms Peak Envelope Power (PEP)
means the average power
elsas:
as “PEP
an envelope.
supplied
to
the
antenna
(49.5)=2450/50=49 watts Avg.
transmission line by a transmitter
A commonduring
error some
makefrequency
calculat- cycle
one radio
at theiscrest
the modulation
ing average power
theyof
multiply
PEP
envelope taken under normal
by .707, i.e. 98 watts times .707. This reoperating conditions.”
sults in an incorrect answer of 69.3 watts.
Understanding the definition of
Power is always calculated by squaring
PEP, the question then arises,
the voltage and
dividing
the result
by the
what
is meant
by “radio
frequency cycle at the crest of the
load impedance.
modulation envelope”? See
7. PEP Power
figure 10.3. The crest of the
Figure 10.3 SSB Modulation
modulation
envelope is the peak
The International
Telecommunication
value; this oscilloscope labels it
Union (ITU) Radio Regulations define the
The modulation envelope duration is
as “Max”. It is 197 volts. Note that the scope calculated the RMS voltage as
terms Peak Envelope
Power
overRF
thecarrier.
entire display
duration.
At
86.6 volts
which(PEP)
wouldas:
be correct for25mS
a steady
However,
here the
modulation is not a steady carrier, but
represents
minimum
and
7.3instead
MHz, this
durationthe
contains
182,500
“PEP means the average power supmaximum modulation levels as an envelope.
individual radio frequency cycles. Since
plied to the antenna transmission line by
The modulation envelope duration isthe
25mS
overcalculates
the entireRMS
display
duration.
scope
voltage
over all
a transmitter during one radio frequency
At 7.3 MHz, this duration contains 182,500 individual radio frequency cycles.
these cycles, we cannot rely on that calcycle at the crest
of the modulation
enve- RMS voltage over all these cycles, we cannot
Since
scope calculates
culation.
relynormal
on thatoperating
calculation.
So, how do we
obtain the RMS voltage for one radio
lope taken under
condifrequency cycle? We know by examining the scope display that there must
tions.”
be at least one radio frequency cycle at the crest of the modulation
envelope.
The peak
Understanding
the definition
of value
PEP, of that cycle is 197 volts. We also know that RMS
voltage equals .707 times the peak voltage; so 197 x .707=139.3 volts. To
the question then arises what is meant by
calculate PEP power, we again use this formula:
“radio frequency cycle at the crest of the
modulation envelope”?
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
Page 59
(c) preciseRF 2013-2016
!U s e r ’ s
G u i d e
-
A p p l i c a t i o n
N o t e
So how do
we obtain the RMS voltSee Figure 10.4, the PEP output of an
p r e c i s e R F D P M 6 0 0 0 P O W E R M E T E R
age for one radio frequency cycle? We
AM transmitter at full modulation is four
know by examining the scope2display that
Pavg=(ERMS) /R . PEP means
there must be atthe
least
one radio
fre-So we can
average
power.
quency cycle atsubstitute
the crest of
thefor
modulaPEP
Pavg. Thus:
tion envelope. The peak value
of that cyPEP=(ERMS)2/R
cle 197 volts. We also know that RMS
Accordingly, applying this
voltage equals .707 times the peak voltformula yields:
age; so 197 x .707=139.3 volts. To calcuPEP = (139.3)2=19,404/50=
late PEP power we again use this for388 watts.
mula:
See Figure 10.4. The PEP
Figure 10.4 Approximately 90% AM
2/R of an AM transmitter at
Pavg=(ERMS)
output
modulation
full modulation is four times its
carrier PEP; in other words, a
PEP means the average power. So we
timesrated
its carrier
other
100-watt amateur transceiver is usually
for noPEP;
moreinthan
25words,
watts a
can substitute PEP
for output
Pavg. Thus:
carrier
when operating in AM100-watt
mode. amateur transceiver is usually
rated for no more than 25 watts carrier
PEP=(ERMS)2/R
26. DIGITAL POWER METERS
output when operating in AM mode.
There are
varietyyields:
of power meters available from Tektronix, Agilent, Krytar,
Accordingly, applying
this aformula
Fluke and others. These power meters provide laboratory grade accuracy
2=19,404/50=
PEP = (139.3)
and
are expensive. Power meters from HP such as the 436A and 438A are
available refurbished and are more affordable on eBay.
388 watts.
27. LABORATORY GRADE POWER METERS
Power meters are generally sold without sensors. Sensors for these power
meters can be more expensive then the entire meter. All laboratory grade
power meters are provided with power reference oscillators or POWER
REFERENCES. These oscillators provide a power reference of 0 dBm (1mW)
generally at a frequency range from 10-50 MHz. They feature laboratory
grade performance. All have, in addition to power reference, some type of
GPIB programability. Unlike the typical power meter used in ham radio
applications, these power meters have NIST calibration and certification.
DPM6000 POWER METER
DPM6000 Appnote V4 .pages
Page 60
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
Figure 11.2 KRYTAR 9000B Power Meter
While discontinued power meters can be purchased on eBay and other
sources for affordable prices, calibrations and sensors are still fairly
expensive.
Figure 11.3 HP 438 Power Meter
Up until the introduction of the DPM6000 from PreciseRF, no new lab grade
power meter was available for under $1,500.
28. POWER METER FOR HAM RADIO
Power meters for ham radio generally are designed to measure transmitter
power in the ham radio frequency spectrum. Typically, they are delivered
with a directional coupler which is placed in-line with the transmission feed
line.They measure forward and reflected power to measure SWR, losses and
antenna performance. They typically have accuracy of 5% to 10%.Newer
units feature digital operation and remote directional couplers. Most meters
of this type do not include a calibration source such as a POWER
REFERENCE. They are, however, feature rich and are easy to use. Prices for
these units range from $200-$500. The LP100 depicted below is a typical
example.
Recently, new microprocessor controlled power meters have become
available which provide the accuracy and dynamic range of lab grade
power meters and the convenience and power handling capacity required
for ham radio operators. These power meters provide both directional
couplers and microwave sensors. Most include POWER REFERENCE signal
sources and extensive measurement capability aided by built-in
microprocessors. These units are available from $500 -$1500.
DPM6000 Appnote V4 .pages
Page 61
(c) preciseRF 2013-2016
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
29. ANALOG RF POWER METERS
Absent a PEP function, virtually all
!U s e r ’ s
analog power meters measure
average power. Many low cost
power meters are notoriously
XII.Analog RF Power Meters
inaccurate as they are typically not
Absent a PEP function, virtually all
calibrated to a known power
standard.
analog power meters measure average
power. Many low cost power meters are
The Bird model 43®, and Heathkit®
HM-102 are exceptions. Their
notoriously inaccurate as they are
accuracy is guaranteed to better than 5% of full scale. The HM-102 employs
typically not calibrated to a known power
an internal accurate calibration standard to which the meter is calibrated.
standard.
The Bird® 43 slugs are individually calibrated
at the factory against an
e r ’ s G u i d e - A p p l i c a t i o n N o t e
accurate RF power source.!U
As as result,
these two analog power meters are often
much more accurate than 5%. The
15. PEP RF Power Meters
XII.Analog
RF Power Meters
accuracy of any meter can be verified to
You may notice that your oscilloscope
Absent
PEP function,
all
bettera than
2% (the virtually
scope vertical
PEP measurements are consistently
analogamplifier
power meters
measure average
specification)
when an
higher than that obtained by most RF watt
used meters
to measure
power.oscilloscope
Many low costispower
are the power
and comparing
that
result
notoriously
inaccurate as
they
are to an unknownmeters. There is nothing wrong. That is
power meter.
because the oscilloscope, with its very
typically not calibrated to a known power
fast rise time, can measure PEP based
You may notice that your oscilloscope PEP
standard.
measurements are consistently higher on peak voltages. Most commercially
than that obtained by most RF watt meters.
available watt meters display average
There is nothing wrong. That is because
power only.
Figure 12.1 Bird 43 Power
the oscilloscope, with its very fast rise
time, can measure PEP based on peak
Some
RF meters
employ
a “PEP”
The Bird
model 43®,
and
Heathkit®
voltages. Most commercially available watt
meters
display
average
power
function such as the Heathkit HM-2140.
HM-102 are an exception. Their accuracy
only.
They do this with a sample and hold
is guaranteed to better than 5% of full
Some RF meters employ a “PEP” functioncircuit.
suchThis
as the
Heathkit®
circuit
needs toHM-2140.
have a fast
scale.
The
HM-102
employs
an internal
They do this with a sample and hold circuit.
This
circuit
needs
to
have
fastthe
rise time, i.e. considerably faster a
than
rise time, i.e. considerably faster than theaccurate
PEP envelope
components.
Even
calibration
standard to
which the
PEP envelope components. Even then,
then, some of these meters may not
meter is calibrated. The Bird® 43 slugs
accurately measure the true PEP
are individually calibrated at the factory
FigureAs
12.1
Bird 43 Power
power.
a result,
their PEP reading
can be significantly lower. One of the against an accurate RF power source.
The Bird model 43®, and Heathkit®
most reliable ways to confirm the
HM-102 are an exception. Their accuracy
As a result, these two analog power
accuracy of any analog or digital power
is guaranteed
better
than
of full
meter istoby
using
an5%
oscilloscope
with a meters are often much more accurate
Figure 12.2 Heathkit HM 2140
scale. calibrated
The HM-102
employs
an
internal
vertical amplifier and
than 5%. The Power
accuracy
Meterof any meter can
sufficient
bandwidth
(normally
twice
the
accurate calibration standard to which the
be verified to better 2% (the scope
frequency).
meter measured
is calibrated.
The Bird® 43 slugs
some of amplifier
these meters
may not accurately
vertical
specification)
when an
are individually calibrated at the factory
against
an accurate RF power source.Page 62
DPM6000 Appnote
V4 .pages
As a result, these two analog power
meters are often much more accurate
measure the true
PEP to
power.
As a result,
oscilloscope
is used
measure
the
(c)
2013-2016
their PEP
reading
canpreciseRF
bethat
significantly
power
and
comparing
result to an
lower. One of the most reliable ways to
unknown power meter.
confirm the accuracy of any analog or
G
1
P
h
m
b
fa
o
a
p
fu
T
ci
ri
P
so
m
th
lo
co
d
o
a
(n
p r e c i s e R F
D P M 6 0 0 0
P O W E R
M E T E R
DPM6000 POWER METER DEVELOPMENT TEAM
The DPM6000 was created by: Firmware, ECB, and digital design: Robert
Kirkpatrick KI6HNA, circuit design & user guide: Roger M. Stenbock
W1RMS, Manufacturing and sales: Audrie Crane, Web design: Travis
Cannon, Document review: Florene Stenbock.
ABOUT THE AUTHOR
The PreciseRF DPM6000 power meter was created by retired Tektronix
engineer, Roger M.
Stenbock (W1RMS).
He has a life-long
passion for
electronics. At
Tektronix he worked
on a number of 7000
series oscilloscopes
and was on the
development team
for the 7A22
differential amplifier
and was a design
engineer for the 2200
series oscilloscopes FG501, FG502, FG503 andFG504 function generators
and PG 501 pulse generator. He is the inventor of four US Patents covering
oscilloscope trigger circuits and on-line flight planning software. Besides his
ham radio activities, he enjoys working in his electronic lab, motorcycling
and glider flying.
<end>
Draft: DPM6000 Appnote V4 .pages
DPM6000 Appnote V4 .pages
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(c) preciseRF 2013-2016
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