Radio interference though cable in computer?

Question

I have my cable hooked up to my compter tv tuner and I can hear a local radio station through my computer speakers. If I disconnect the cable from the wall or the tv tuner the sound goes away but so does the tv on the computer obviously. Any help?

Answer 1

Jayson:

Basically when you connected the cable tuner to your laptop you connected a nice long antenna to the tuner and the laptop that picks up the signal from the AM radio station.

First try shortening the cable between the tuner and the laptop to as close to zero as possible.  If the problem goes away then you know the source for the problem.  Get some rectangular ferrite torroidal cores from Radio Shack. They are rectangular and about 1" by 1 1/2" and have a large opening.  At the laptop end of the cable that goes between the tuner and laptap wind as many turns of the cable as you can on to this torroidal core.  This is called a torroidal RF choke.  Position the chokes right at the connectors.  First try a torroidal core on the connector at the laptop. This isolates the cable and keeps it from acting like an antenna feeding RF (radio frequency) energy from the radio station into your laptop which then acts like a radio to demodulate the audio from the signal, amplify it and feed it to your speakers.  If this doesn't work then wind another torroidal core at every connector one by one until the problem is resolved.  Also wind a torroid at the cable input to the computer speakers even if they do not have a connector and one where the cable from the wall adapter enters the speaker.  

If all these torroidal cores do not resolve the problem then we will have to do more brute force things.  Meanwhile, get the following data:

1)  How far is the radio station antenna from your location?  The distance to the antenna helps determine the solution.  

2)  What is the transmit power of the station.  You can find this from FCC data on the web or by simply calling the station engineer.  

3)  Is it a day and night station?  I.e. is the problem worse during the day when the station is running 50KW than at night when it is only running 5 KW?

You may also want to get a copy of the RFI Book from the ARRL.  Go to WWW.ARRL.ORG and click on the section for ordering literature.  It is the best document on the market for addressing these kinds of RFI (Radio Frequency Interference) problems.  There is no more complete presentation of solutions to these kinds of problems than this document.

Good Luck and 73 from the Fisherman

Answer 2

what the fisherman said...