[TenTec] Omni VI audio problem

[Jim Brown]

On 9/17/2018 7:25 PM, Bob McGraw K4TAX wrote:
> I wouldn't bother with chokes as any noise from the computer or interface will appear in mike audio.   Just the way it works. Bummer.

Every Ten Tec rig I've seen has a Pin One Problem at the rear chassis 
RCA connectors. The FIRST thing to get power for EVERYTHING IN THE 
STATION from the same power outlet, or from outlets that share the same 
green wire. If what you're hearing is AC powerline buzz, that helps, 
often by 20 dB.

The second thing to do is to bond chassis-to-chassis from each piece of 
gear in your station, especially those in the audio path. That includes 
the computer. Chassis of a computer can usually be found on the 
retaining screw(s) of DB-series connectors, like those used for video, 
parallel printer ports, and serial ports. There should be a 
chassis-to-chassis bonding wire running in parallel with every 
unbalanced cable, especially those in the audio path, but also any 
control cables (like RS232).

If you still have issues, open up the radio and bond the shield contact 
to the chassis as close as possible to the point of entry.

I agree with Bob that an audio transformer should not be helpful or 
necessary if the above has been done.

I also agree with Bob that IF the noise noise is coming out of the 
computer sound card on the hot conductor, it MAY be useful to increase 
the audio drive from the computer and add a 20 dB passive attenuator at 
the radio. That's a simple voltage divider with a 10:1 ratio -- that is, 
something like 1K in series and 100 ohms in parallel with the radio's 
input. But it is unlikely to help if, as I strongly suspect, that it's a 
Pin One Problem, in which case the bonding should make a big dent in it.

73, Jim K9YC