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.
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