[Kenwood] Alternator whine

[Mike Clarson]

Bill: Alternator whine can be a tough one. Ground loops are often a source
of the whine. Also, is the whine AM or FM modulating the carrier. If its AM,
it is AC from the alternator getting in the power lead and modulating the
carrier. To test, connect a diode (1N34 is great, but a 1N914 or 1N4148 or
other high speed switching diode should work just fine) across the input of
an audio amplifier (battery operated preferred) held within a foot or so of
the antenna is a good probe. If, when you key the radio, all you hear is a
pop, then it is not AM. If you hear the whine, then it is AM. If whine is
FM, then it is getting in the low level stages of the radio. Try to figure
out how to key the radio without the microphone plugged in. See if it still
happens. Next, try isolating the radio from ground, (remove from bracket,
place on seat, use a mag mount antenna insulated from the vehicle by a
plastic bag) and see what happens. Also, try to measure the ammount of AC on
the battery terminals. Connect a VOM across the battery terminals with test
lead in the output position (or a .47uf cap in series with one of the
probes) and see how much AC voltage is there. Don't have to key the radio,
but car needs to be running. Report back with some data and some suggeations
will be offered. --Mike, WV2ZOW

-----Original Message-----
From: kenwood-bounces at mailman.qth.net
[mailto:kenwood-bounces at mailman.qth.net]On Behalf Of B Riches
Sent: Tuesday, June 29, 2004 4:52 PM
To: kenwood at mailman.qth.net
Subject: [Kenwood] Alternator whine


Any comments or cures for alternator whine on transmit from fm units?  Truck
in question is 2003 Ford 450 diesel with twin batteries.  Alternator was
replaced and noise is less but still there.  Power cables from radio go
directly to the battery that is closest to alternator.  Tried Newmar 10 amp
inline filter in radio power line but made no difference.

73,

Bill Riches, WA2DVU
Cape May, NJ