[Elecraft] KPA500 RFI problem

[Rick Bates]

I agree that the balun should be checked but that it is likely NOT the issue
here as it works on the other bands.  If it is replaced, using a 1:1 common
mode choke (not just a voltage balun or series of ferrite cores on the coax)
would be a good thing to try.  I opted for the 10KW rated version as I never
want to have an issue and I only run <700 watts.

To make clear an earlier statement of mine, without the added coax, the
untuned VSWR was 24:1, with the added coax it is under 10:1.  The KAT500
tuned the wire in both cases here  but in the original configuration tuned
my EDZ to 1:1 at low power then faulted out at anything above 300 watts.
Adding more coax solved the issue (I tried a shorter run too, no change) by
shifting the 80M voltage peak to someplace else on the feed.  

Is your wire antenna insulated or bare?  Is there a chance that it is arcing
(wet tree, mast ???)?  With the voltages produced at QRO, the potential is
there.  Ditto your window line, insulated or bare?  Is rain or snow
impacting it?  You'd know because it would need retuning.

Rick wa6nhc

-----Original Message-----
From: David Gilbert

 From a troubleshooting point of view jumping right to the balun 
requires making a lot of assumptions, most of them unwarranted given 
what little we know so far from his post.   More importantly, a balun 
with a ruined core is going to look bad for SWR no matter what power 
level is fed to it, and he says that things look fine at 300 watts but 
go south at 400 watts.  That's an arc over problem somewhere ...

Dave   AB7E