21-533.fm Page 1 Thursday, August 5, 1999 3:47 PM Cat. No. 21-533 OWNER’S MANUAL Please read before using this equipment.
1-533.fm Page 2 Thursday, August 5, 1999 3:47 PM INTRODUCTION Your RadioShack CB/Ham Field-Strength 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 matches the transmitter’s output impedance as closely as possible. The meter’s standing wave ratio (SWR) function helps you trim your antenna to the precise length you need for the maximum transmitted power.
21-533.fm Page 3 Thursday, August 5, 1999 3:47 PM CONTENTS Measuring SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Connecting the Meter . . . . . . . . . . . . . . . . . . . . . . . . . . Calibrating the Meter/Measuring SWR . . . . . . . . . . . . . Interpreting SWR Readings . . . . . . . . . . . . . . . . . . . Improving SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measuring Field Strength . . . . . . . . . . . . . . . . . . . . . . . .
21-533.fm Page 4 Thursday, August 5, 1999 3:47 PM MEASURING SWR Measuring SWR shows you how much of your radio’s transmit power is reflected from the antenna back into the antenna cable, 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 maximum power they are capable of producing. For more information about measuring SWR, see the ARRL Handbook, available at your local library.
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 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.
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 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.
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 reading of 1.5 also means that 4% of your signal power is lost.
21-533.fm Page 8 Thursday, August 5, 1999 3:47 PM Interpreting SWR Readings An ideal SWR reading is 1.0, but this reading is usually possible only under laboratory conditions or with a dummy load. Actual antenna installations have higher readings. The information below will help you interpret the readings you get. SWR 8 Efficiency Interpretation 1.0 to 1.5 Excellent The antenna cable and the antenna length match the transmitter’s output requirements almost perfectly. 1.5 to 2.
21-533.fm Page 9 Thursday, August 5, 1999 3:47 PM IMPROVING SWR There are several ways to improve the SWR of your radio/antenna combination. Try these first. • Be sure you are using the type of cable recommended for your equipment. If the manufacturer recommends a 50ohm cable, do not substitute another type that has a different impedance. • Confirm that you mounted your antenna according to the manufacturer’s instructions. The angle and the base arrangement can affect the SWR reading.
21-533.fm Page 10 Thursday, August 5, 1999 3:47 PM MEASURING FIELD STRENGTH Your meter can measure the low levels of radio frequency (RF) generated by a radio transmitter. You can use these measurements to map the transmitting direction and coverage pattern of your antenna, or to compare your radio and antenna’s efficiency before and after an adjustment. You do not need to connect the meter to the antenna or the radio to measure field strength. It takes two people to measure field strength.
21-533.fm Page 11 Thursday, August 5, 1999 3:47 PM 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.
21-533.fm Page 12 Thursday, August 5, 1999 3:47 PM 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.
21-533.fm Page 13 Thursday, August 5, 1999 3:47 PM For example, for a 50-foot diameter circle: 50 feet 11.46 = 4.363 Feet 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 station identification. 1.
21-533.fm Page 14 Thursday, August 5, 1999 3:47 PM 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 transmit 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.
21-533.fm Page 15 Thursday, August 5, 1999 3:47 PM • 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.
21-533.fm Page 16 Thursday, August 5, 1999 3:47 PM 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 antenna mounted on the rear bumper of an automobile that is parked facing north.
21-533.fm Page 17 Thursday, August 5, 1999 3:47 PM USING FIELD STRENGTH READINGS TO TUNE YOUR RADIO AND ANTENNA You can use field strength measurements to monitor the effectiveness of changes you make to your radio and antenna while you make them.
21-533.fm Page 18 Thursday, August 5, 1999 3:47 PM Then, while the helper holds down the transmit key, walk around and adjust the meter’s knob until the meter’s needle 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.
21-533.fm Page 19 Thursday, August 5, 1999 3:47 PM 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 enjoy it for years. Keep the meter dry. If it gets wet, wipe it dry immediately. Liquids can contain minerals that can corrode the electronic circuits. Handle the meter gently and carefully.
21-533.fm Page 20 Thursday, August 5, 1999 3:47 PM Modifying or tampering with your meter’s internal components 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 local RadioShack store for assistance.
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21-533.fm Page 22 Thursday, August 5, 1999 3:47 PM SPECIFICATIONS Measurable RF Power ..................................... 1–1000 Watts SWR ................................................................................ 1–3 Impedance .............................................................. 50 Ohms Frequency Range ................................................. 3–30 MHz Dimensions (HWD) ...................... 2 9/16 ¥ 6 5/16 × 3 15/16 Inches (65 ¥ 160 ¥ 100 mm) Weight .............................
21-533.fm Page 23 Thursday, August 5, 1999 3:47 PM Limited Ninety-Day Warranty This product is warranted by RadioShack against manufacturing defects in material and workmanship under normal use for ninety (90) days from the date of purchase from RadioShack company-owned stores and authorized RadioShack franchisees and dealers.
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