Radio Shack Marine Instruments 21 533 User Guide

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Cat. No. 21-533  
OWNER’S MANUAL  
Please read before using this equipment.  
CB/Ham Field-Strength  
SWR 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 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  
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MEASURING SWR  
Measuring SWR shows you how much of your radio’s transmit  
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. Set CALIBRATION/FS/SWR on the front of the meter to  
CALIBRATION/FS.  
2. Turn on your radio. Then select a channel or frequency  
on your transmitter and hold down its transmit key. Do not  
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-  
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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 the meter’s  
knob until the needle points to CAL.  
4. Release the transmit key, then set CALIBRATION/FS/SWR  
to SWR.  
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5. Press the transmit key again, then read the SWR by not-  
ing 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 reading of 1.5 also means that 4% of your signal  
power is lost. However, 96% of the radio power is more  
than enough for almost all applications.  
6. Repeat Steps 1–5 for each channel or frequency you  
want to get an SWR reading for.  
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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 or with 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  
2.0 to 3.0  
Very good  
The antenna, the cable, and  
the transmitter operate very  
efficiently.  
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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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 dif-  
ferent impedance.  
• Confirm that you mounted your antenna according to the  
manufacturer’s instructions. The angle and the base  
arrangement can affect the SWR reading.  
• Adjust the length of your antenna according to the  
instructions provided by the manufacturer. A change of  
1
as little as /8 inch can make a measurable difference.  
• See your radio’s and antenna’s owner’s manuals.  
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MEASURING FIELD STRENGTH  
Your meter can measure the low levels of radio frequency (RF)  
generated by a radio transmitter. You can use these measure-  
ments to map the transmitting direction and coverage pattern  
of your antenna, or to compare your radio and antenna’s effi-  
ciency before and after an adjustment. You do not need to con-  
nect the meter to the antenna or the radio to measure field  
strength.  
It takes two people to measure field strength. For an accurate  
measurement, you will need to map the site around your anten-  
na. Then, while someone presses the radio’s transmit key, you  
will need to walk around the site around your antenna with the  
meter, marking the readings you see.  
Hints:  
• In addition to the meter, we recommend you use the fol-  
lowing items to help you measure field strength:  
— Several photocopies of the template on Page 11  
— 36 objects such as rocks or weighted pieces of paper  
— 25 feet of rope or strong cord  
— Calculator  
— Pencil  
— Compass  
• Make sure there is at least 25 feet of open space in all  
directions around your antenna.  
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PREPARING THE ANTENNA SITE  
Before you use the meter to measure field strength, you should  
mark the site around the antenna in a pattern that will help you  
make the measurement.  
An easy way to do this is to map the area around your antenna  
using a template like this one.  
Antenna Location  
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The template shows an imaginary circle around an antenna.  
The spokes on the template represent imaginary straight lines  
measured from the center of the circle to 36 points spaced  
equally around the circle. Each straight line is 25 feet in length.  
The numbers on the template (1–5) are a guide to show you  
where to mark the field strength level the meter displays as you  
measure.  
Hint: To help measure a circular path around the antenna, tie  
a slip knot in a 25-foot piece of rope or strong cord, slide the  
knot loosely around your antenna, then use the rope as a guide  
as you walk around the antenna.  
Follow these steps to prepare the antenna site.  
1. Starting at the antenna, use a compass to find due north.  
Then walk due north and stop about 15 to 25 feet away  
from the antenna.  
2. Use an object such as a rock or a weighted piece of paper  
to mark where you are standing.  
3. Walk around the antenna in a circle, using more objects to  
mark 35 more evenly spaced marks on the path.  
Hint: You can quickly find the space to leave between each  
mark by using a calculator. Measure the diameter of the  
marked circle (from one side of the circle to the other). Then,  
divide the diameter by 11.46.  
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For example, for a 50-foot diameter circle:  
50 feet  
= 4.363 Feet  
11.46  
So, you would place a mark every 4.363 feet (4 feet, 3 inches).  
CALIBRATING THE METER/  
MEASURING FIELD STRENGTH  
Important:  
Be sure to follow any radio service regulations that  
limit the amount of time you can transmit without a break or sta-  
tion identification.  
1. Remove the supplied short wire antenna attached to the  
bottom of the meter, then insert it into FS ANT on top of the  
meter.  
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2. Set CALIBRATION/FS/SWR to CALIBRATION/FS.  
3. To calibrate the meter, have your helper select a channel  
or frequency on your transmitter and hold down its trans-  
mit key. Tell the helper not to speak into the microphone.  
Then, while the helper holds down the transmit key, walk  
around inside the marks you made using the steps in  
“Preparing the Antenna Site” on Page 11, covering as  
much area inside the circle as you can. As you walk,  
watch the meter’s needle. If it moves to the right of 5 on  
the FIELD STRENGTH scale, rotate the knob on the front  
of the meter until the needle lines up with 5 on the scale.  
Notes:  
If you use a CB that has sideband modes (SSB), do not  
select any of these modes. (Use only AM for field  
strength measurements).  
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If you have an amateur radio, select the continuous  
wave (CW) or tuning mode to check the field strength.  
4. To measure field strength, as the helper continues to hold  
down the transmit key, move to the marked spot on the  
circle due north of the antenna, then watch the meter’s  
needle.  
Note the reading on the FIELD STRENGTH scale and  
place a dot on the template on Page 11 corresponding to  
the reading at that point.  
In this example, the needle shows a 4 on the FIELD  
STRENGTH scale. Place a dot where the spoke repre-  
sentating the path you walked from the center of the circle  
intersects the circle marked with a 4 on the template.  
Direction of Travel  
Dot  
You are Here  
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5. Move to each marked spot along the circular path then  
repeat Step 4 for each one, taking another reading and  
recording that reading on the template.  
Here is an example of a completed template. It shows an an-  
tenna mounted on the rear bumper of an automobile that is  
parked facing north. The field strength readings form a two-  
lobed pattern when plotted, meaning the antenna’s power is  
greatest at the front, weaker at the back, and almost nonexist-  
ent at the sides.  
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USING FIELD STRENGTH READINGS  
TO TUNE YOUR RADIO AND ANTENNA  
You can use field strength measurements to monitor the effec-  
tiveness of changes you make to your radio and antenna while  
you make them. Changes you might make include:  
• Installing a new antenna or antenna cable  
• Adjusting the length of an antenna  
• Changing the antenna mount on your vehicle  
• Adjusting your radio’s transmitter  
You do not need to connect the meter to the antenna or the ra-  
dio to measure field strength, but you will need two people.  
While someone presses the radio’s transmit key, you will need  
to note the readings you see on the meter.  
Important:  
Be sure to follow any radio service regulations that  
limit the amount of time you can transmit without a break or sta-  
tion identification.  
1. Remove the supplied short wire antenna attached to the  
bottom of the meter, then insert it into FS ANT on top of the  
meter.  
2. Set CALIBRATION/FS/SWR to CALIBRATION/FS.  
3. To calibrate the meter, have your helper select a channel  
or frequency on your transmitter and hold down its trans-  
mit key. Tell the helper not to speak into the microphone.  
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Then, while the helper holds down the transmit key, walk  
around and adjust the meter’s knob until the meter’s nee-  
dle moves to 3 on the FIELD STRENGTH scale.  
Notes:  
If you use a CB that has sideband modes (SSB), do not  
select any of these modes. (Use only AM for field  
strength measurements).  
If you have an amateur radio, select the continuous  
wave (CW) or tuning mode to check the field strength.  
4. Have the helper release the transmit key, then make a  
change to your radio or antenna (such as adjusting the  
antenna or transmitter or adding a new antenna).  
5. When the change is completed, have the helper hold  
down the transmit key again while you watch the meter’s  
needle.  
If the field strength reading is higher, you have probably  
improved the power output and efficiency of your radio  
and antenna. If the field strength reading is lower, repeat  
Steps 4 and 5.  
Note: If you move the physical location, or change the  
transmission direction, of your antenna, you might have to  
recalibrate the meter and measure the field strength  
again. See “Calibrating the Meter/Measuring Field  
Strength” on Page 13.  
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CARE AND MAINTENANCE  
Your RadioShack CB/Ham Field-Strength SWR Meter is an  
example of superior design and craftsmanship. The following  
suggestions will help you care for your meter so you can en-  
joy it for years.  
Keep the meter dry. If it gets wet, wipe it dry im-  
mediately. Liquids can contain minerals that can  
corrode the electronic circuits.  
Handle the meter gently and carefully. Dropping  
it can damage circuit boards and cases and can  
cause the meter to work improperly.  
Use and store the meter only in normal temper-  
ature environments. Temperature extremes can  
shorten the life of electronic devices and distort  
or melt plastic parts.  
Keep the meter away from dust and dirt, which  
can cause premature wear of parts.  
Wipe the meter with a damp cloth occasionally  
to keep it looking new. Do not use harsh chem-  
icals, cleaning solvents, or strong detergents to  
clean the meter.  
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Modifying or tampering with your meter’s internal compo-  
nents can cause a malfunction and might invalidate the  
meter’s warranty and void your FCC authorization to operate  
it. If your meter is not operating as it should, take it to your lo-  
cal RadioShack store for assistance.  
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SCHEMATIC DIAGRAM  
(illus - show schematic diagram  
of meter)  
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SPECIFICATIONS  
Measurable RF Power ..................................... 1–1000 Watts  
SWR ................................................................................ 1–3  
Impedance .............................................................. 50 Ohms  
Frequency Range ................................................. 3–30 MHz  
Dimensions (HWD) ...................... 29/16 ¥ 65/16 × 315/16 Inches  
(65 ¥ 160 ¥ 100 mm)  
Weight ............................................................................ 8 oz  
(226 g)  
Specifications are typical; individual units might vary. Specifi-  
cations are subject to change and improvement without no-  
tice.  
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Limited Ninety-Day Warranty  
This product is warranted by RadioShack against manufacturing defects in ma-  
terial and workmanship under normal use for ninety (90) days from the date of  
purchase from RadioShack company-owned stores and authorized Ra-  
dioShack franchisees and dealers. EXCEPT AS PROVIDED HEREIN, Ra-  
dioShack MAKES NO EXPRESS WARRANTIES AND ANY IMPLIED  
WARRANTIES, INCLUDING THOSE OF MERCHANTABILITY AND FITNESS  
FOR A PARTICULAR PURPOSE, ARE LIMITED IN DURATION TO THE DU-  
RATION OF THE WRITTEN LIMITED WARRANTIES CONTAINED HEREIN.  
EXCEPT AS PROVIDED HEREIN, RadioShack SHALL HAVE NO LIABILITY  
OR RESPONSIBILITY TO CUSTOMER OR ANY OTHER PERSON OR EN-  
TITY WITH RESPECT TO ANY LIABILITY, LOSS OR DAMAGE CAUSED DI-  
RECTLY OR INDIRECTLY BY USE OR PERFORMANCE OF THE PRODUCT  
OR ARISING OUT OF ANY BREACH OF THIS WARRANTY, INCLUDING,  
BUT NOT LIMITED TO, ANY DAMAGES RESULTING FROM INCONVE-  
NIENCE, LOSS OF TIME, DATA, PROPERTY, REVENUE, OR PROFIT OR  
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,  
EVEN IF RadioShack HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH  
DAMAGES.  
Some states do not allow the limitations on how long an implied warranty lasts  
or the exclusion of incidental or consequential damages, so the above limita-  
tions or exclusions may not apply to you.  
In the event of a product defect during the warranty period, take the product and  
the RadioShack sales receipt as proof of purchase date to any RadioShack  
store. RadioShack will, at its option, unless otherwise provided by law:  
(a) correct the defect by product repair without charge for parts and labor; (b) re-  
place the product with one of the same or similar design; or (c) refund the pur-  
chase price. All replaced parts and products, and products on which a refund is  
made, become the property of RadioShack. New or reconditioned parts and  
products may be used in the performance of warranty service. Repaired or re-  
placed parts and products are warranted for the remainder of the original war-  
ranty period. You will be charged for repair or replacement of the product made  
after the expiration of the warranty period.  
(continued)  
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(continued) This warranty does not cover: (a) damage or failure caused by or at-  
tributable to acts of God, abuse, accident, misuse, improper or abnormal usage,  
failure to follow instructions, improper installation or maintenance, alteration,  
lightning or other incidence of excess voltage or current; (b) any repairs other  
than those provided by a RadioShack Authorized Service Facility; (c) consum-  
ables such as fuses or batteries; (d) cosmetic damage; (e) transportation, ship-  
ping or insurance costs; or (f) costs of product removal, installation, set-up  
service adjustment or reinstallation.  
This warranty gives you specific legal rights, and you may also have other rights  
which vary from state to state.  
RadioShack Customer Relations, Dept. W, 100 Throckmorton St., Suite 600,  
Fort Worth, TX 76102  
We Service What We Sell  
3/97  
RadioShack  
A Division of Tandy Corporation  
Fort Worth, Texas 76102  
811081260A  
3A8  
Printed in China  
 

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