90 Lincoln TC Radio Buzz >4mph

What part of the the electrical/electronics generates an fairly constant 300 HZ signal (sounds like a harsh buzz) that can be heard on the AM radio band over weak
stations when going more than about 4 MPH? It goes away when the antenna is disconnected from the radio so it apparently doesn't go thru the +12 V, and is apparently an RF noise (like spark plug noise). Is there any circuit connected to a motor/relay/solenoid/valve (an inductance) that only operates when going above about 4 MPH (forward or reverse)?
No tech here knows/cares.
Thanks -JMM
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hi JMM - have you changed out your spark plug wires???
the reason you are getting the static is because you picking up RF energy that is being introduced into the antenna lead. since it is not probably being picked from the portion that is sticking out of the car, you will have to look at the cable run that the lead is in. now, chances are, you pick up the unusual stuff when it goes by a area of higher current applications, such as power windows. you might hear a compliant about every time they roll down the passenger's side window, they hear it in the radio, but no other windows will cause it.
the key to where to look is your 4 mph symptom. as the rpm's pick up, if it is the spark plugs wires, you will hear a repeating sound, but if you alternator suppression circuit is shot, you will hear a buzzing sound, since that is the type of static it produces.
as a quick check. pop off the fan belt, and start the car and rev it up. if you don't have any static on your radio, you just cut your problem solving time a lot.
best of luck.
~ curtis
knowledge is power - growing old is mandatory - growing wise is optional
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c palmer wrote:

The key word here is "constant" if it were a bad plug wire or alternator garbage, the noise or whine would go up and down in frequency with RPM.
But new plugs/wires/dist cap are always a good idea if it has not been done in a long time.
Any electrical work done on the car? Under the dash such as climate control? Its probably picking up some radiation from a wiring harness not put back properly if its not engine noise. probably computer generated hash.
BOB
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Have you got an aftermarket radio or is this with the factory one? I am on my second car with a similar problem. Both are Fords. The first was an '84 and the current one is a '95. The '84 was fine with the factory radio but like you describe with aftermarket ones. I don't know about the '95, the factory unit was already gone when I got it. It might be an antenna problem, my '84 got better when I put in a plain stick antenna. The '95 has the antenna in the rear window.
Ask around and find the best car stereo shop in your area and ask them. I doubt the guys at the big-barn shops will know, tho.
PoD

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