In , "Randy" wrote:

snip
I thought that because the whine went away when I disconnected the coax that
the problem was not related to the power supply and one of those noise
filters would not be of much use.


You said the noise is not present on your broadcast radio, which tells me that
the noise isn't coming from the antenna. If the noise goes away when you
disconnect the coax then it must be being picked up by the coax shield. If the
coax shield were grounded then the CB would not hear the noise. Since the coax
shield is connected to the chassis of the CB, that means the CB isn't grounded
(by 'grounded' I mean an RF ground). The radio should be grounded by mounting it
directly to the metal chassis and using a very short negative power lead. The
noise filter helps prevent noise from any possible ground-loops or other RF
feedback paths.


My biggest obstacle is that this is a company truck. The CB, radio and TV
are all using these antennas thru some kind of combiner.


......yikes!


Running new coax
would mean drilling holes in the cab. I am not sure how my boss would feel
about this. If it were my truck I would rip it all out and start from
scratch but I must do the best I can with what I have.


Your boss wants you to deliver the payload in the shortest amount of time with
the least amount of hassles. To do your job well, local communication with a
good CB is -extremely- helpful, and almost essential for a long-haul driver.


The antennas are mirror mounts. I have been reading about grounding. I
thought that two antennas actually were better on the fiberglass vehicles
because they could create a ground plane between each other. My antennas use
a plastic insert to keep them from being grounded to the mirrors. If I
ground them would this short out the transmitter?


Dual antennas have no practical advantage over a single antenna in a mobile
installation. They do not create a ground plane between them, nor do they work
as a counterpoise to each other. They do look cool, but if I were you I would
just use one and avoid the hassle.

As for the antenna mount, the shield of the coax should be -well- connected to
the chassis (ground-plane), and the center conductor to the antenna. The plastic
insert is used to keep the two apart. If you disconnect the coax at the radio
and check it with an ohmmeter (center conductor to the shield), it should be
wide open; i.e, -not- shorted.


I appreciate your feedback Frank, I know that it is difficult to diagnose
something from a distance but I am willing to try anything except routing
new coax.


Don't spend -your- time or money -- convince your boss that you need a CB radio,
then get him to have his contracted radio shop do a proper installation. That's
what most trucking companies do, and I'm suprised your's doesn't.






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