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Very strange - receiver pickup up am radio signal

 

New member
Username: Jslost

Post Number: 1
Registered: May-08
I just hooked up my computer to my receiver by extending a mini jack using three seperate lines of speaker wire. The sound quality is great, however, for some reason the input on my receiver (AUX/Video, etc..) is somehow picking up an AM radio signal??? It is very low volume and can barely be heard when music is playing from the computer. How is this possible? Did I somehow create an AM antenna??? Thanks for any help. jA
 

Silver Member
Username: Magfan

USA

Post Number: 229
Registered: Oct-07
Yep, antenna it is.
You need to come up with a troubleshooting strategy. Disconnect and/or re-run wiring, being careful not to bunch them up, maybe.
See if you can borrow a power conditioner?
Problem may be coming in on the AC?

Bottom line is to start changing things until the problem gets worse or better, than you'll know which direction to go.
 

New member
Username: Jslost

Post Number: 2
Registered: May-08
Ok, I have done some research and figured out where the problem lies.

The AM interference comes when the minijack is plugged into the computer, AND when any other cord is also plugged into the computer (power, monitor, usb, etc...) Even with the computer off it still picks up the signal. I went to radio shack and bought two RF chokes, but they aren't at all effective. Any suggesions? Should the chokes work, and if so, how should they be installed in this scenario. I also realize now that there is a local radio station antenna less than 1 mile from me...perhaps I just can't stop it because its so close?

Thanks for any help.
 

New member
Username: Nk4k

Atlanta, Ga Usa

Post Number: 1
Registered: Dec-08
J:
I'm guessing here, because I don't know the complete set-up. I'm assuming you're using amplified (externally to the sound card) speakers. If this is the case, you must use the snap-on ferrite cores AT the speaker inputs and not necessarily only at the computer. Adding at both ends is not unusual, because your audio connector is probably making a nice little detector that changes the radio to audio.
There are other strategies: WAD UP the speaker cable at the box or at the computer. Wrap cable in aluminum foil and ground it to the computer case. Open speakers and bypass (connect across) the inputs with 0.1uF to 0.01uf at 200 V ceramic capacitors (what you can find and/or what actually works). Do this on the sound card, too, at the jack.
You will need as many wire loops inside the RadioShack ferrites as possible. Try a "wad" method and then try the "loop" method. The wad just puts equal length back-and-forth wire loops inside the ferrite; the loop method actually loops the wire around the ferrite material -- both as many as you can get. Another suggestion is use shielded wire or shorten length of the speaker cables.
Last resort is to consult an expert, either the radio station engineer or a local ham radio operator. KEEP IN MIND, HOWEVER, they are under no obligation to help you or to change the interfering transmitter in any way (under federal law), so put your ultra-diplomatic hat on before visiting the station. Local Ham Radio Clubs (google this term plus your city/state) have teams to help with this type of problem, but only if a ham radio operator is causing the problem. You can pretend at first you don't know which, heh heh heh...
If you want to learn about interference, there are chapters in radio publications available at http://www.arrl.org. Click on "catalog and store" and search with key "interference." The Radio Amateur's Handbook that the ARRL sells has an entire chapter on it. Some of the bigger stores like Amazon.com and/or Barnes & Noble have these books on their web pages as well, as do www.hamradio.com, www.aesham.com, up to 20 others (gigaparts, Burghardt, Associated Radio, R&L Electronics, Universal Radio) -- all reputable.
My experience with this is that you will spend lots of time on it until you find some trivial solution that is hard to believe (like relocating the computer into bedroom #2).
Hope that helps.
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