[Amps] RF in the Audio

[Jim Brown]

On 9/23/2011 8:41 AM, Robert Kirkland wrote:
> hi,
> There have been several posts on rf in the audio recently, this is for 
> info, it happened to me. When I fired up my Ten-Tec Jupiter one 
> morning the guys complained. Checking the TT diagram showed 2 ground 
> pins in the mic connecter a chassis ground and an audio ground that 
> wandered around inside the box to the audio board. That's bad, any rf 
> on the mic cable goes on in. Connecting the grounds together and to 
> the mic shield fixed it. Bought a built up K3 and wired my mic 
> connecter cable and grounds together, nice, until the morning I 
> returned after a long vacation rf again. A field strength meter showed 
> rf on the co-ax, rf on the K3, rf on the 76A, rf every where. Dropped 
> the antenna, cleaned and re taped the 1:1 balun co-ax connecters, ok. 
> Moral is "don't patch it up find it and fix it".

It is generally a good thing to seriously choke all feedlines to keep 
common mode RF off of them. Not only does common mode current conduct 
into the shack and excite Pin One problems like you have described, but 
it can also radiate into your neighbor's stereo,and it can pick up RF 
noise and couple it to your antenna.

73, Jim K9YC