In , "Randy" wrote:


"Frank Gilliland" wrote in message
.. .
In , "Randy" wrote:

I drive a 9900 International. I am getting a loud whine in the CB
speaker,
but not in the radio speakers, even though they share the dual antennas.
The
whine increases and decreases with the rpms of the motor. After
disconnecting the coax from the CB transceiver the whine is gone. Does
this
mean the coax or antennas are definitely the problem? ... or are they
just
picking up on a problem with the alternator? The coax will be extremely
hard
to replace, maybe impossible since this is a company truck. The
alternator
would probably be easier to repair.

Any help to eliminate or even reduce the whine would be greatly
appreciated.


What brand/model radio are you using?




I am using a Cobra 29 NW right out of the box.

Antennas are 4' Firestiks II

swr ~ 3


Your SWR is high. High SWR isn't responsible for whine, but it is a good
indicator of other problems. From what you said in your other post your cab roof
is fiberglass, so you don't have any ground plane -at all- for your antenna. But
even that isn't responsible for the whine. I suspect that the radio isn't very
well grounded. The mounting bracket should be bolted directly to the dash or
some other chassis metal, and the negative power lead should be as short as
possible (inches) to the same. You can also try a noise filter on your positive
power lead, and tap the wire as close to the radio as possible. That should
eliminate your whine. It should also get your SWR down below 3.

As for your antenna, you need to find a point on the rig where the antenna can
be mounted directly to the chassis. A mirror mount is ok if the bracket and door
are well grounded. A 9' whip on the front bumper isn't a bad choice either
(don't forget to tie it back a bit so it doesn't flop around). You could also
try one of those 'no-ground-plane' antennas but don't expect great results. Ask
around the watering holes and see what others have done.





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