Radio Shack 21-533 User Manual
21-533.fm Page 1 Thursday, August 5, 1999 3:47 PM
Please read before using this equipment.
CB/Ham Field-Strength
Cat. No. 21-533
OWNER’S MANUAL
SWR Meter
21-533.fm Page 2 Thursday, August 5, 1999 3:47 PM
INTRODUCTION
Your RadioShack CB/Ha m Field- Strengt h SWR Meter hel ps
you tune your CB or amateur radio system for the best performance.
CB and amateur radio syste ms work best when the antenna
system’s impedance matches the transmitter’s output impedance as closely as possible. The meter’s st anding wave
ratio (SWR) f unction helps you trim your antenna to the precise length you need for t he ma ximum transmitted power.
The meter’s field strength function helps you position your
antenna for the best coverage and determine the effectiveness of changes you make to your antenna, antenna cable,
and transmitter.
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 precaut ions provided wi th the equipment you are testing.
You need a separate 50-ohm coaxial cable (such as
Note:
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.
© 1998 Tandy Corporation.
RadioShack is a registered trademark used by Tandy Corporation.
All Rights Reserved.
2
21-533.fm Page 3 Thursday, August 5, 1999 3:47 PM
CONTENTS
Measuring SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Connecting the Meter . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Calibrating the Meter/Measuring SWR . . . . . . . . . . . . . 5
Interpreting SWR Readings . . . . . . . . . . . . . . . . . . . 8
Improving SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Measuring Field Strength . . . . . . . . . . . . . . . . . . . . . . . . 10
Preparing the Antenna Site . . . . . . . . . . . . . . . . . . . . 11
Calibrating the Meter/Measuring Field Strength . . . . . 13
Using Field Strength Readings to Tune Your Radio
and Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Care and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3
21-533.fm Page 4 Thursday, August 5, 1999 3:47 PM
MEASURING SWR
Measuring SWR s hows you h ow much of your r adio’ s transmi t
power is reflected from the antenna back into the antenna c able, generating heat and wasting power. With t his informat ion,
you can adjust the le ngth of your ant enna or antenna cabl e so
your antenna and radio combination can produce the maximum power they are capable of producing.
For more information about measuring SWR, see the
Handbook
, available at your local library.
ARRL
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 st eps to connect the meter to your radio and antenna.
4
21-533.fm Page 5 Thursday, August 5, 1999 3:47 PM
1. Turn off your radio. Then disconnect the antenna from
the radio and plug it into
meter.
2. Plug the coaxial cable into the radio’s antenna jack and
TRANSMITTER
into
on the back of the meter.
ANTENNA
on the back of the
CALIBRATING THE METER/
MEASURING SWR
CALIBRATION/FS/SWR
1. Set
CALIBRATION/FS
.
on the front of the meter to
2. Turn on your radio. Then select a channel or frequency
on your transmit ter and hold down it s transmi t key. Do
speak into the microphone.
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-
not
5
21-533.fm Page 6 Thursday, August 5, 1999 3:47 PM
mit on several channels, choose a frequency in the
middle of the range of channels you use. (For exampl e,
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 the meter’s
knob until the needle points to CAL.
4. Release the transmit key, then set
SWR
to
.
6
CALIBRATION/FS/SWR
21-533.fm Page 7 Thursday, August 5, 1999 3:47 PM
5. Press the transmit key again, then read the SWR by noting the needle’s position on the upper SWR scale. A
meter reading of 1 on the upper scale is ideal.
SWR Scales
The figure shown between the upper and lower scales on
the meter (% REF POWER) indicates the percentage of
power that is wasted through reflection of the signal from
the antenna back into the antenna cable. For example,
an SWR readin g of 1.5 also means that 4% of your si gnal
power is lost. However, 96% of the radio power is more
than enough for al mo st al l applications.
6. Repeat Steps 1–5 for each channel or frequency you
want to get an SWR reading for.
7
21-533.fm Page 8 Thursday, August 5, 1999 3:47 PM
Interpreting SWR Readings
An ideal SWR reading is 1.0, but thi s reading is usually possible only un der l abor atory condi tions or wit h a du mmy l oad. Actual antenna installations have higher readings. The information 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
transmitt er’s out put requirements 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 cabl e, and
the transmitter operate with
some loss. If possible, adjust
your antenna or antenna
mounting system to i m prove.
Above 3.0 Inefficient Adjust your antenna or
antenna mounting system to
improve efficiency.
8
Loading...