[Elecraft] RFI in audio chain

Jan Ditzian ditzian at windstream.net
Tue Dec 22 20:40:48 EST 2015


This is a wrap-up post to the discussion about RFI feedback into the 
audio of my K3.

First, I want to thank everyone who offered suggestions, most of which I 
tried to follow up.

After numerous failures, I managed to lure a local guru--a ham who makes 
his living getting RF and audio things to work.  After ten minutes of BS 
in my ham shack, he said to start disconnecting each wire from the back 
of the K3, one-by-one.  Some of you may have told me to do the same 
thing, and I remember approximating that, but somehow I must have messed 
up.  At any rate, as soon as we disconnected the line from my outboard 
USB sound card to the rear input of K3, used for digital work, the audio 
RFI went away.  My friend says he thinks that an isolated line would be 
better, but the fact that I have a stereo output going directly to the 
mono input is probably the real culprit.  At the moment, only hours 
since his discovery, I have successfully worked on 80 and 40 meters with 
the amplifier, but I have not yet fixed up an isolated digital line.

My thanks to the entire K3 community who attacked this problem.

I am now using the original vertical, fed with patched lengths of 
hardline, with a hardline, wound choke at both ends.  Each choke is 
40-50 feet long.

I also discovered that my RF ground point in the shack (back of the 
Ten-Tec KW tuner), shows 30-50 ohms resistance vis-a-vis the electrical 
ground terminals in the shack.  Another rod as part of my RF ground 
system may be forthcoming.

73,

Jan, KX2A



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