View Full Version : Radio and Electronics
05-05-2003, 09:12 PM
why is it that when i'm listening to the radio and turn on something electric (such as my keyboard... the instrument; not computer... or the sewing machine), it makes the radio get alot of static?
05-05-2003, 10:34 PM
Some electric devices, such as motors, switches, and musical instruments throw off magnetic fields and stray electromagnetic "noise" that your radio interprets as legitimate radio signals. Better shielding and better grounding would help, but it's hard to add after-the-fact. Make sure all your signal cords are clean and tight. Some musicians even go to the trouble of lining the instrument inside with copper foil, with a ground wire, to isolate the inner wiring from spurious noise. It's a big hassle, but you get cleaner sound.
Some folks, who have paranoia as a hobby, see the brain as an electronic device subject to outside radio interference. They wear aluminum foil hats to prevent mind control. I'm not an engineer, and I can't quite explain why this is folly, but I'm pretty sure it is.
The spurious signal is a pain in the gazoo. I have a nice TV that throws off a buzz to my big-bucks audio reciever's AM section when I try to get the radio announcer during a TV ball game. I gnash my teeth at the machinery. There may be a solution beyond gnashing, but I don't know what it is.
05-06-2003, 06:20 AM
I had a room mate who had a blow dryier which would make any reception impossible in a large area. I suggested she sell it to the US military to use as electronic warfare.
The reason you hear static is those appliances radiate electromagnetic noise which can arrive atthe receiver through the air or through the wiring. The problem can be alleviated, if not totally resolved, with adequate filtering and shielding. These days appliances are better designed in this respect than they used to be. Also, cars ignitions used to be awful offenders. there is still a motorcycle which, when it goes down my street, makes reception imposible.
05-06-2003, 07:53 AM
Computers are a big culprit here, but their noise is more patterned than, say, a blowdrier's. This leads to what's known as tempest attacks (http://www.eskimo.com/~joelm/tempestintro.html), where someone sitting across the street can see what's on your monitor by picking up radio signals.
Of course, this can be deliberately used by someone other than the NSA. Tempest for Eliza (http://www.erikyyy.de/tempest/) is a computer program that writes patterns to your monitor to create specific patterns in the monitor's RF emissions that an AM radio can pick up as music. The latest version can even play MP3s this way. It's a very cool geek toy. :)
05-06-2003, 08:00 AM
This thread is a duplicate of this one (http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=182025), which has more replies.
05-06-2003, 09:21 AM
If the noise is interfering with an AM receiver, one idea is to use an antenna/pre-amp (http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SM100) that only responds to the signal's magnetic field.
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