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.
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.
on Sep 18, 2010 | Car Audio & Video