I had a similar problem many years ago with an L-4B amp. 
I wonder if adding ferrite to the coax would solve this problem?
GL
N2TK, Tony

-----Original Message-----
From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Jim
Kvochick
Sent: Tuesday, November 18, 2014 9:16 PM
To: elecraft@mailman.qth.net
Cc: k...@att.net
Subject: [Elecraft] Strange K3 & KPA500 Issues fixed with a longer coax
cable?

I've stumbled into a strange problem.

I have 4 friends with similar K3 stations to my own; K3 >>> KPA500 >>>
KAT500.  The stations are powered with similar power sources.

One station sounds fine, works great.  The other 4 had strange issues that
manifested themselves as audio distortion when running the amplifier.  After
looking all over for RF and grounding issues, we swapped the coax cable from
the K3 to the amplifier, with a longer cable (about 6 to 7 feet - largely
because that was the only free cable we had handy).

Making the cable from the K3 to the amplifier longer eliminated the issue.
putting the cable back brought the problem back.  Making a new short cable
still left us with audio distortion.   The only thing that seemed to solve
the issue in all 4 cases was making the K3 to amplifier cable longer. 

This got me to investigate my own station.  It turns out that the cable I
used between the amplifier and the radio was about 6 feet long.  Swapping
this cable for a shorter length brought about audio distortion symptoms.

Does anyone have any thoughts about this?

Cheers

Jim K8JK

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