[UK-CONTEST] RF Feedback

[Ian White, G3SEK]

Cooper, Stewart wrote:
>In setting up my station for this year's CQ WW SSB I have discovered that my
>constantly tripping Alpha 91 is caused by RF feedback getting into the Heil
>mic. It's not a problem that is immediately obvious on my transmitted audio.
>In fact, no one has ever mentioned anything, and it is worse on some bands
>(10m) than others. What I need is some real world practical advice to
>eliminate the problem. Perhaps that advice might help others with a similar
>problem. I use a Heil ProSet headset with a DX Doubler, MFJ 432 DVK and
>FT1000MP. Now, the DX Doubler doesn't appear to add to the problem and the
>MFJ might appear to, but I run it on internal batteries and the problem
>remains even when it's out of circuit. I use a ferrite toroid on the headset
>mic cable before it enters the DX Doubler. I have tried earthing all the
>components in the shack to the same earth 'bus' although this (for audio
>equipment) might not be a good idea. Any other suggestions?

A definite recommendation is a clip-on RF current meter. That will tell 
you how much RF current is going where, so you can see if your ferrets 
are in the right places, and what the effects they are really having. 
It's the best RFI investigation tool going.

It might also be worth trying a larger, wider ground bus made from PC 
board, and trying to group all the I/O connections towards one end - see 
'In Practice' a few months ago.


-- 
73 from Ian G3SEK