Radio Shack 21-534 User manual

Cat. No. 21-534
OWNER’S MANUAL
Please read before using this equipment.
CB/High-Frequency Ham
Power SWR Meter
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© 1998 Tandy Corporation.
All Rights Reserved.
RadioShack is a registered trademark used by Tandy Corporation.
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INTRODUCTION
Your RadioShack CB/High-Frequency Ham Power SWR
Meter helps you tune your CB or amateur radio system for
the best performance.
CB and amateur radio systems work best when the antenna
system’s impedance closely matches the transmitter’s out-
put impedance. The meter’s standing wave ratio (SWR)
function helps you trim your antenna to the precise length
that produces the maximum transmit power. The meter’s
power meter function measures your radio’s peak envelope
power (PEP) or average power.
Carefully read all of these instructions to get the best use
from this meter.
Warning: You can use this meter to make measurements on
equipment that uses high voltages. Carefully observe all
safety precautions providedwith the equipmentyou are test-
ing.
Note: You need a separate 50-ohm coaxial cable (such as
RG-58U) with a PL-259 connector connected to both ends
(such as Cat. No. 278-968, not supplied), long enough to
reach from your radio’s antenna jack to the back of the
meter.
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CONTENTS
Measuring SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Connecting the Meter . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Calibrating the Meter/Measuring SWR . . . . . . . . . . . . . 5
Interpreting SWR Readings . . . . . . . . . . . . . . . . . . . . . 8
Improving SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Measuring Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Care and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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MEASURING SWR
Measuring SWR shows you how muchof your radio’stransmit
power is reflected from the antenna back into the antenna ca-
ble, generating heat and wasting power.With this information,
you can adjust the length of your antenna or antenna cable so
your antenna and radio combination can produce the maxi-
mum power they are capable of producing.
For more information about measuring SWR, see the
ARRL
Handbook
, available at your local library.
CONNECTING THE METER
To connect this meter to your CB or amateur radio and your
antenna, you need RG-58U coaxial cable (not supplied) with
a PL-259 connector on both ends (such as RadioShack Cat.
No. 278-968). The cable must reach from the back of the
meter to your radio’s antenna jack.
Follow these steps to connect the meter to your radio and an-
tenna.
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1. Turn off your radio. Then disconnect the antenna from
the radio and plug it into ANTENNA on the back of the
meter.
2. Plug the coaxial cable into the radio’s antenna jack and
into TRANSMITTER on the back of the meter.
CALIBRATING THE METER/
MEASURING SWR
1. Turn on your radio. Then set FUNCTION on the front of the
meter to CAL.
2. Select a channel or frequency on your transmitter and
hold down its transmit key. Do
not speak into the micro-
phone.
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Notes:
• An SWR reading will be different for different frequen-
cies (channels). If you transmit on one channel more
often than any other, select that channel. If you trans-
mit on several channels, choose a frequency in the
middle of the range of channels you use. (For example,
if you transmit on all 40 CB channels, choose Channel
20, because it is midway between Channel 1 and
Channel 40.)
• If you use a CB that has sideband modes (SSB), do not
select any of these modes. (Use only AM for SWR
measurements.)
• If you have an amateur radio, select the continuous
wave (CW) or tuning mode to check the SWR.
3. While you hold down the transmit key, rotate CALIBRA-
TION on the front of the meter until the needle points to
CAL.
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4. Release the transmit key, then set FUNCTION to SWR.
5. Press the transmit key again, then find the SWR by read-
ing the appropriate scale on the meter.
• If your transmitter’s power is less than 20 watts, read
the lower scale (marked with an L on its right side)
• If your transmitter’s power is more than 20 watts, read
the upper scale (marked with an H on its right side)
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INTERPRETING SWR READINGS
An ideal SWR reading is 1.0, but this reading is usually possi-
ble only under laboratory conditions orwith a dummy load.Ac-
tual antenna installations have higher readings. The in-
formation below will help you interpret the readings you get.
SWR Efficiency Interpretation
1.0 to 1.5 Excellent The antenna cable and the
antenna length match the
transmitter’s output require-
ments almost perfectly.
1.5 to 2.0 Very good The antenna, the cable, and
the transmitter operate very
efficiently.
2.0 to 3.0 Acceptable The antenna, the cable, and
the transmitter operate with
some loss. If possible, adjust
your antenna or antenna
mounting system to improve.
Above 3.0 Inefficient Adjust your antenna or
antenna mounting system to
improve efficiency.
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When you measure SWR, use this chart to determine the per-
centage of power that is wasted through reflection of the signal
back to the radio.
For example, an SWR reading of 1.5 also means that 4% of
your signal power is lost. However, 96% of the radio’s power is
more than enough for almost all applications.
IMPROVING SWR
There are several ways to improve the SWR of your radio/an-
tenna combination. Try these first.
• Be sure you are using the type of cable recommended for
your equipment. If the manufacturer recommends a 50-
ohm cable, do not substitute another type that has a differ-
ent impedance.
• Confirm that you mounted your antenna according to the
manufacturer’s instructions. The angle and the base
arrangement can affect the SWR reading.
SWR 1.0 1.1 1.2 1.5 2.0 2.5 3.0
Ref.
Power
(%)
0 0.22 0.8 4.0 11.1 18.4 25.0
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• Adjust the length of your antenna according to the instruc-
tions provided by the manufacturer. A change of as little as
1/8inch can make a measurable difference.
• See your radio and antenna’s owner’s manuals.
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