Hi all... I know I've mentioned this in here before, but I've changed some things and I thought I'd run it by everyone to see if I could get some great ideas from the people who know about Audi electronics and radios... I have a 45 Watt VHF transceiver in my car, which is mounted in my glove box (I use it for EMS purposes, and am authorized to ). It connects to an antenna, which is mounted on the front right fender inside the engine compartment lip towards the rear, and the coax for it runs directly into the glove box, not near any other wires or anything at all, except some plastic equipment. The power cord for the radio (which runs about 12A when transmitting) runs from the glovebox, behind the radio, behind the steering column under the knee bolster, up through the ECU box and into the engine compartment and connects to the battery directly, both +12V and ground. The problems: 1) When the car is on, and the radio is receiving, I get a decent amount of static and a horrible alternator whine (gets higher pitched with engine revvs). This problem is non-existent with the car off. 2) When I transmit on the radio, though it does transmit fine, there is a horrible buzzing/thumping sound in all the car's audio speakers, only when the car is on, and regardless of whether the radio is on. That's the gist of the problem, and I know this isn't normal for this forum but I figure you guys know all about audio amps and wiring and that sort of thing, as well as Audi's, and figured maybe someone would have some good advice on solving either of these problems. Thanks so much!

1. Get a good noise filter on the power in to the VHF radio.
Contact a special radio place for this. Don't skimp on this, it's crucial.

2. You are still pumping out 45 watts of transmitting power that is simply over-whelming any type of other trasmited signal.
Your car FM/AM radio is on, and even though the frequencies are different, the fact that you are transmitting 45 watts on *any* signal is gonna over-whelm *any* receiver.
This is true even if you radio is off. BTW-it's not really off. There is still power going to it, the head unit and the power amp. Your tranmitter is simply jumping that part of the "off" circuitry. You are pushing out so much tranmitting power in a confined space, it's simply finding the shorest path to an open circuit.
Pehaps a better shielded antenna may help, but really, its all that power.

Can you elaborate on the noise filter? I don't know how that works. Also, I had a theory that the alternator whine is because the radio is grounded at the battery. Is that possible, or do you think its the power cable? Should I get a noise filter for each? How much do these cost?

Also, are you saying that there's no way to eliminate the buzzing during transmit? I understand all that you're saying, but where I get confused is why other vehicles (i.e., police cars, ambulances) don't have the same problem with their radios.

Do a 'google search on '20 amp noise filter'<ul><li><a href="http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&amp;category%5Fname=CT LG%5F007%5F002%5F004%5F000&amp;product%5Fid=270%2D055">noise filter</a></li></ul>

i plan on doing that, but i don't go back to work for a couple more weeks, and hoped to get this resolved before then! thanks though!