[Elecraft] RFI in audio chain

[Don Wilhelm]

Jan,

Toroids on the mic cord may help, but the real solution is to eliminate 
the RF on the outside of the coax shield in the antenna field.
Refer to the writings of Jim Brown K9YC for effective baluns (he prefers 
common mode chokes because balun is not a specific thing - some good, 
some bad).
Look at chapters 6 and beyond of 
http://audiosystemsgroup.com/RFI-Ham.pdf to eliminate the theory and get 
right to the subject of constructing effective common mode chokes for HF.

Keeping RF out of the shack is your first measure of defense.  Cure the 
antenna field problems and if there are still problems, then try 
ferrites on the station equipment lines.

73,
Don W3FPR



On 11/22/2015 6:02 PM, Jan Ditzian wrote:
> I have a problem that appears to be changing, but I could use some 
> help.  The problem is RFI in the audio input (microphone input) when I 
> use my vertical antenna on 40 meters.  Here is a rundown of what has 
> happened:
>
> I have a 67-foot elevated vertical that I can use on 80 and 40, and it 
> works fine on CW.  However, on SSB, both bands, there clearly is 
> feedback; there is no feedback on the other bands where I use a C3 
> yagi.  Initially, the feedback was so bad that the rig would go into 
> oscillation, and I had to turn the amp to standby.
>
> I recently purchased the new KSYN3A and decided to install it.  I 
> replaced the K3 with my IC-730 backup, using the hand microphone that 
> came with the 730.  The 730 did not have any RFI.  I finished the 
> modification and returned the K3 as the operating rig.  Now, the RFI 
> on 40 seems to have diminished substantially or disappeared, but it 
> still happens on 75/80.  However, it seems to be much less there as 
> well.  I do not suspect that the KSYN3A had anything to do with this, 
> but perhaps I tightened connections better when I returned the rig to 
> service.  I also redid some ground connections.
>