Tip & How-To about Car Audio & Video

Problems in CB Radio Receive and Modulation

Much of the time complaints about CB receive (RX) and modulation are caused by problems in the antenna system. Make sure there are no shorted or open connections in the coaxial cable or PL-259 (screw-on connectors for coaxial cable, located at the antenna and rear of CB radio) connectors. Use your radio's meter or better still, a Power/SWR meter to check the SWR (Standing Wave Ratio) of the antenna. Try to get that as close as possible to a 1:1 ratio on the meter. A shorted or open antenna can keep the receive audio on your radio at very low levels. Plus, this will harm your transmitter if you continue keying the mike.

Another problem can surface in the radio itself. This will be noticed if you can transmit, but have no "modulation". Modulation can be described as the voice heard above the "carrier" (your transmitted signal). Every CBer knows about the term, modulation. The Truckers will definitely inform you about your modulation quality...lol. This problem can be caused by a defective AMC (Automatic Modulation Control) stage in the receiver circuit. Also, there will be no modulation upon transmit.

One other thing could be causing this lack of receive audio. Defective wiring or switching in the microphone can result in no audio. Additionally, in many radios, a missing mike will not allow receive, because the microphone connection completes the RX (Receive) circuit.

Solutions:
1. Check the antenna system, and fix any problems.
2. Check mike, or substitute another one.
3. Using meter, and/or another radio for listening on same channel, check power and receive.
4. You can probably fix 1, 2 and 3 yourself, or with the aid of a friend.
5. AMC problem in radio (as described above) will require professional service from a CB (Citizens Band) repair facility.

The above suggestions and advice will assist in repairing the majority of the symptoms described.

Regards, Bill

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1 Answer

Why does my new Honda CB always show RX receiving transmission no matter where squelch is set?


if this is on a Goldwing, it appears that you have a shorted pin int he connector. Disconnect the radio and make sure all of the pins are straight and connecting properly.

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MAKE SURE R-F GAIN IS TURNED UP FULLY AND ANTENNA IS NOT SHORTED

Feb 22, 2013 | Uniden Bearcat Pro PC68XL 40-Channels Base...

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I can receive, but not broadcast from my CB radio.


Hi mfdogman,

This problem is usually one of two things. Check the antenna coaxial cable and connections first, to be assured there are no shorts. That's one of the symptoms of receive and no transmit. The other would more than likely be a defective RF Transmitter stage in the final amplifier circuit. That could be a defective (blown or shorted) Power Transistor or IC (Integrated Circuit) Module.

After checking the antenna and coax, key the Radio up and look for any meter or indicator sign of TX (Transmitted power). If you have a power meter, use that for power and SWR (Standing Wave Ratio which should be close to 1:1 ratio) checks of the radio and antenna system. If there is no power, then you will need Technical help from a Professional at a repair facility, unless you are familar with this work. The antenna problem, if it exists...you should be able to fix.

Let me know when you get this fixed, and contact me again for more help. Thanks.

Regards, Bill

Sep 18, 2010 | Midland 77-285AXL 5-Channels Base CB Radio

1 Answer

will not get good recepiton.


Hi stormnorm157,

Much of the time this is caused by problems in the antenna system. Make sure there are no shorted or open connections in the coax or PL-259 connectors. Use your radio's meter or better still, a Power/SWR meter to check the SWR of the antenna. Try to get that as close as possible to a 1:1 ratio on the meter. A shorted or open antenna can keep the audio receive on your radio at very low levels. Plus, this will harm your transmitter if you continue keying the mike.

Another problem can be in the radio itself. This will be noticed if you can transmit, but have no "Modulation". Modulation can be described as the voice heard above the "Carrier" (your transmitted signal). Every CBer knows about the term, Modulation. The Truckers will definitely inform you about your modulation quality...lol. This problem can be due to a defective AMC (Automatic Modulation Control) stage in the receiver circuit. And, there will be no modulation upon transmit.

One other thing could be causing this lack of receive. Defective wiring or switching in the microphone can result in no audio. Or, in many radios, a missing mike will not allow receive, because the mike connection completes the RX (Receive) circuit.

Solutions:
1. Check the antenna system, and rule that out or fix.
2. Check mike, or substitute another one.
3. Using meter, and or another radio for listening on same channel, check power and receive.
4. You can probably fix 1 and 2 yourself, or with a friend.
5. AMC problem in radio (as described above) will require professional service.

Let me know how this turns out, and inform me if I can offer any more help. Thanks.

Regards, Bill

Sep 18, 2010 | Midland 1001Z 40-Channels Base CB Radio

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