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Old 02-05-2016, 18:46   #1
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Alternator noise on VHF??

Recently I am getting alternator noise on my VHF radio both transmit and receive when the engine is running. This is a new issue. Any wisdom as to the most likely cause? The noise changes frequency with engine speed so I am guessing it is the alternator and not the regulator. Does this mean I have a diode failing or bad brushes or ???
The Alternator is a high output unit (~ 130 amp) and has about 2k hours on it.

I am tempted to just put a filter on the output, but I am afraid the will just be masking whatever the real problem is.
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Old 02-05-2016, 19:17   #2
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Re: Alternator noise on VHF??

Quote:
Originally Posted by BrightAyes View Post
Recently I am getting alternator noise on my VHF radio both transmit and receive when the engine is running. This is a new issue. Any wisdom as to the most likely cause? The noise changes frequency with engine speed so I am guessing it is the alternator and not the regulator. Does this mean I have a diode failing or bad brushes or ???
The Alternator is a high output unit (~ 130 amp) and has about 2k hours on it.

I am tempted to just put a filter on the output, but I am afraid the will just be masking whatever the real problem is.
===

I'm guessing a little but I'd be inclined to suspect a failed diode. Unless you're comfortable with disassembling it yourself, I'd recommend taking it to an auto electric shop and have them check it out. Here's a good article on troubleshooting alternator noise in aircraft radios.

Licking Alternator Whine - AVweb Features Article
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Old 02-05-2016, 20:25   #3
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Re: Alternator noise on VHF??

I have seen bad batteries do it too. as the battery is the filter for the DC system. and a new battery got rid of it. but could also be alt.
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Old 04-05-2016, 10:24   #4
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Re: Alternator noise on VHF??

You might have some luck in reducing it by putting ferrites on to the wires going to the radio (except the antenna lead). Check out the radio forum on here. I think it has some info on getting rid of noise on radios in general.
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Old 04-05-2016, 10:46   #5
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Re: Alternator noise on VHF??

Pretty sure a diode if it just started, and as you are apparently aware, there are noise filtering capacitors that can be put on alternators to help eliminate the noise, you see them on aircraft all the time.
But like you said it would be a band aid, with 2,000 hours on it, I'd say it due for an overhaul anyway, lots cheaper if you do it before a bearing or brushes fail.
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