Ask Sail: VHF Whine

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NOISE ON THE BOAT NEGATIVE LINE

Q: I have a new fixed-mount VHF radio, and I have severe alternator whine on both transmit and receive. My old radio did not, even though it was on the same 12V DC line. The manufacturer says new digital radios are more sensitive to alternator noise. However, I had my Balmar 100-amp alternator rebuilt, it checked out, and the noise persists when running the engine. I’ve also tried chokes, added grounding and added more filters that Balmar suggested, with no success. The only thing that did work was your earlier suggestion of trying the radio on a small 12V DC battery. (Except when I touched the black wire to the ship’s DC negative black wire.) I need this lifesaving radio to work when underway under power.

Bill Ailes, Hartsville, PA

GORDON WEST REPLIES

Try the 12V DC line rewired directly to the battery as a test. Red to battery positive. Black to battery negative, NOT to a convenient ship ground point. Run the engine. If you still have noise, have Balmar contact me, so I might better understand why their alternator whine is bleeding through the DC output of their gear. If memory serves you have conventional flooded battery. Therefore, with your well-filled battery acting as a giant noise buffer capacitor, the alternator should not make noise on transmit and receive. Got a well-watered battery? When a ship’s battery runs low on electrolyte, it can no longer buffer noise. Check for water over the top of the plates.

January 2018

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