Batboard

I have a VHF radio installed in a 2005 International truck, it's producing a whine in the transmit audio when the engine is running. The noise is coming in through the electrical wiring. Radio is wired directly to the battery. I have tried a noise supressor, but with no luck.

Does anyone have any suggestions or advice to offer?
thanks

Try moving the connection of your ground wire.... Also, check your antenna ground.

I have tried moving the ground from one battery to the other, no difference.

I assume the ground on the antenna is good enough. The radio will power up even if the negative wire is not grounded (it's getting ground from the antenna instead).

really.....does the whine vary with the RPM of the engine? or is it constant.

First thing, get the ground off the battery and put it on the chassis. The reason for not grounding directly to the battery is if the ground cable to the engine block comes loose or developes high restisance the truck starter will try to draw it's current thru the body ground strap and possiably thru your radio that has it's mounting and antenna on the body and still has a direct battery ground. If you must ground to the battery put a fuse in the ground also.

Now to the whine, what model radio is this. Where is the power and ignition control lead coming from?

Yes, the whine is variable with the RPM.

There is a fuse installed on the negative lead.

Icom IC-F521, Does not use ignition sense lead. Positive power is obtained directly from the battery terminal.

Could also be a sign that your battery ground is getting flakey. Check the integrity of your ground lead from battery negative to chassis ground. Of course that includes the clamp and making sure the post is clean of crud.

Or it could be that you've lost a diode or two in the alternator and that soon you'll be replacing the alternator.

Thanks for the replies.
I suspect it is the alternator. I will probably have a pretty good fight to get them to replace it since it is still charging.

[quote="tc792"]Thanks for the replies.
I suspect it is the alternator. I will probably have a pretty good fight to get them to replace it since it is still charging.[/quote]


You might try using a digital voltmeter and measure the AC compnent on the output of the alternator. Put the meter on the AC range and as low as it will go. Then look for some milivolt AC voltage. You might see 2 or 3 millivolts and that is fine. Much over that and you have a bad diode on the alternator.

Another test you can make is to let the engine idle. Turn on the headlights while measureing the battery terminal voltage. You should see 13.6 to 14 volts Dc or so. Go to highbeam headlight setting. The voltage should stay fairly constant. Then turn on the heater. Not the air conditioning. You may hit a point where the voltage drops down. This indicates you reached the max output the alternator can put out at the idle speed.

Try increasing the RPM slightly and see if the voltage comes up. If the alternator is bad, it will not raise up with the slight increase in RPM.

Jim

tc792 wrote:Thanks for the replies.
I suspect it is the alternator. I will probably have a pretty good fight to get them to replace it since it is still charging.

Had a similar problem with an '03 Supercrew with a noisy alternator. Service department initially declined to replace it (the tester shows it's putting out plenty of amps!)

The ripple was easily visible on an o-scope. Five minutes of preaching at the service manager about ripple and readings on an o-scope and he pretty much said "durrrr... I have no idea what you just said... but we'll go ahead and replace it."