Telephone Interference Solutions

I am picking up CB radio signals on my stereo even when listening to tapes or cd's. Can you help with this problem???

The most common problem is the speaker wire acting as an antenna and feeding the signal into the stereo. You can check this out by completely disconnecting the speaker wires from the stereo and plugging in your headphones to listen (keep the headphone wire short by coiling it up into a tight bundle). If the interference disappears or gets appreciably weaker then you are on the right track.

If this cures the problem, you need a filter choke, that connects between each speaker wire and the stereo. A speaker filter choke can be constructed using a $12.00 toroid (model FT240-43, from Amidon Associates in Santa Ana, CA (phone 714 850-4660) and winding 20 to 25 turns of the speaker wire onto the toroid. This filter choke should be installed between the speaker and the stereo (as close to the stereo as possible). If there is no effect or the interference just gets slightly weaker then it may be that the CB signal is coming into the stereo through the power cord or some other route.

You can purchase a.c line cord RF filters at most electronics outlets. Of course it could be coming in through more than one route.

Also, any other length of wire connected to your stereo can be the culprit. If you have lots of other cables going to other rooms you might try disconnecting them.

Keep all cables including speaker wires as short as possible. Avoid lengths that resonate at the CB band (8-9 feet is a resonant quarter wave length at CB frequencies (27 Mhz).

Click on the picture for RFI filter construction.

RFI Related Links:
American Radio Relay League RFI
Ground Loop Problems
More RFI Links!

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