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On my GMC 4106 there is a lot of static on the radio AM Band. As engine rpm increases so does the pitch of the static. There is none on the FM band. It seems to me that I read there is a diode ( or some device) that goes in the power line to the radio that will prevent this. Does anyone know what this might be?

Thanks

Fred Mc.

Fred
I believe the fix for that is a capacitor/filter on the field lead at the alternator. Now I'm no guru so hopefully someone can confirm this. Are you transmitting this noise with your CB radio as well?

Fred,
   You may have a failed diode in your alternator.  Usually automotive radios have plenty of filtering to eliminate the normal noises.  Consult your manual, it is relatively simple to check the diodes on the 50DN alternator and how to do it is in my manual so I'm assuming it is in yours as well.  With a bad diode the alternator will still work, just not put out it's full power, and the noise generated will overwhelm the best of filters. 
P.S.  Airbag's suggestion of a capacitor on the field won't help and may destroy your regulator.
Regards
Jerry 4107 1120

Quote from: Jerry Liebler on July 01, 2009, 07:14:31 PM
Fred,
   You may have a failed diode in your alternator.  Usually automotive radios have plenty of filtering to eliminate the normal noises.  Consult your manual, it is relatively simple to check the diodes on the 50DN alternator and how to do it is in my manual so I'm assuming it is in yours as well.  With a bad diode the alternator will still work, just not put out it's full power, and the noise generated will overwhelm the best of filters. 
P.S.  Airbag's suggestion of a capacitor on the field won't help and may destroy your regulator.
Regards
Jerry 4107 1120

Thanks Jerry
They are standard in the airplane world but I do not know about the 50DN.

Funny thing about the AM radio. I just stuck one in my coach and there ws an old rooftop andtenna that I tried to use thinking that up high was the answer but all I got was a bunch of static and weak signel. I had a wire hooked to the antenna jack so just tossed it out the door and the signal came in clear. So I ran a wire down to the front bumper and dangled som short wires from it and worked just great. I was out in a canyon where very limited signal were getting in on a fishing trip and still recieving a good signal. Don't ask me why. Jerry