[Elecraft] KPA500 RFI problem

[Rick Bates]

Try altering your feedline length (which means resetting the KAT500 memories
too).  I had a similar issue on 80M.

However in my case, it made no difference when I added 30' more window line
but changing the coax length (+~30') allowed it to load.  The doublet length
is 170' per side (all HOA stealthy too).

I use a 10 KW rated DX Engineering 1:1 common mode choke to convert window
line to coax AND keep RF outside the shack.  Their website has a 'white
paper' comparing 1:1 and 4:1 which is worth reading too.

73,

Rick wa6nhc

-----Original Message-----
From: Ron W3ZV

At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the
KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is
a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to the
KAT500. I have a comment point ground to a ground rod six foot from the
shack. I have operated the amp at 400+ watts from 80m to 6m. The only band
that gives me a problem is 12m. When I am operating at 400 watts ssb, the
amp will fault with a high swr indication within 5 to 20 seconds.
Immediately prior to the fault the swr on the amp display was 1.2:1.
Reducing power to below 300 watts seems to avoid the problem.

Assuming the consensus is that this is RFI, what would be the most likely
suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest
way to diagnose and correct the problem? Thanks

Ron W3ZV