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Old 17-09-2017, 11:57   #1
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Join Date: Jan 2009
Location: Juneau, Alaska
Boat: Prout Snowgoose 37
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Electrical Noise (alternator whine) on VHF


I am trying to troubleshoot an alternator whine on my VHF. Here are my symptoms:

When batteries are charged, and the alternator is not working hard, the whine is minimal, but present. When the engine is off, no whine is present at all.

When batteries are discharged (say 40% down) and the alternator is really working to push the amps in, the whine is horrible - it is hard to hear transmissions sent or received over the whine.

Radio is an ICOM IC-M502, with remote command mic. The radio shares an antenna with my Vesper XB-8000 AIS, through the Vesper antenna splitter. note the Vesper unit shows my VSWR as 1:1.

Alternator is a 150 amp AmplePower unit, complete with the Smart Alternator Regulator. House bank is a 520 amp-hour bank of AGM's.

Alternator passes the diode test, so it doesn't look like i have a bad diode. I have tried adding ferrite chokes to the power cables, running a new, separate cable directly to my 12V bus, all to no avail.

Anyone have suggestions on troubleshooting this one? It has been extremely frustrating.
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Old 17-09-2017, 12:21   #2
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Join Date: Aug 2011
Location: Petersburg, AK
Boat: Outremer 50S
Posts: 3,178
Re: Electrical Noise (alternator whine) on VHF

Do you have an alternator noise filter attached to the alternator? Cheap, that may be the easiest solution, although tracking it to the source is arguably the better solution.

A lot of noise problems are poor ground, either at the alternator or at the radio. Is the alternator ground just through the mounting bolts? If so, add a cable from a case ground on the alternator (a ground stud if it has one, otherwise a case bolt) to the main grounding point where your batteries are connected (presumably to the engine block).

Disconnect the antenna from the radio. If the whine goes away with the antenna disconnected then it may be coming in on the antenna cable. If the whine stays then it is liking coming in on the power cable.

Digging deeper, the ham radio organization ARRL has some pretty good links/info for further analysis: ARRL Automotive Noise
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Old 17-09-2017, 13:40   #3
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Re: Electrical Noise (alternator whine) on VHF

Friend had this issue on his fishing boat with an inboard diesel and he installed a noise filter which cleared up the problem. The antenna test is probably a good idea before getting one.

Marine alternator noise filters.

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alternator, cal, electric, electrical, noise, vhf

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