KPA500 Faulting on high SWR on power rise

Posted by Chris Hallinan on Feb 24, 2018; 5:42am
URL: http://elecraft.85.s1.nabble.com/KPA500-Faulting-on-high-SWR-on-power-rise-tp7638486.html

Greetings from southwest Florida.

My KPA500 is kicking out with REFL HI warning (high SWR).  But here is the
strangeness. My setup is K3->KPA500->40' coax->MFJ 600W remote tuner -> 4:1
balun -> open wire feedline to 80-meter doublet.  In words, I have a remote
autotuner feeding an 80-meter doublet fed with 600-ohm open wire line.  A
Balun Designs 4:1 balun provides the interface from the open wire line to
the tuner.

With the autotuner tuned at low power, the SWR shows 1.5:1 on my KPA500 and
external SWR meter.  As I run the power up to 300, 400, 500 watts,
somewhere in there all of a sudden the SWR instantly jumps off the scale,
into the red LEDs on KPA500, and it faults.  It's as if the SWR were
dependent on power.

Even stranger, when I back the power off to say 250 Watts, holding key down
the SWR is stable in the green (<1.5:1), but when I key it at CW rates, the
SWR bounces into the red on every dit and eventually faults, when at steady
state key down it never leaves the green zone!

I fear it is the tuner falling over, but it should be able to handle the
power.  I see this on all bands from 80-20.

Operating into my 20-meter resonant vertical, with no tuner, everything
works fine.

Any ideas or hints on how to correct this?

Thanks,

Chris
73 de K1AY


--
Life is like Linux - it never stands still.
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