[Elecraft] KPA500 Faulting on high SWR on power rise

[Dave Cole (NK7Z)]

Triage the problem...

Dummy load at the end of the tuner chain-- if it works at high power 
then all is good from the dummy load back, the problem lies downstream 
of the dummy load.  If it fails with the dummy load there, then you have 
a coax problem between the radio and the dummy load.

So far you have done a bit of triaging already, if you operate on the 
vertical, with no tuner, and all is good, then you know the radio and 
amp are OK.  You also know the feed line to whatever type of coax switch 
you have is OK...

Move the dummy load around to triage out as much as possible...

If you don't have a dummy load, you need one...  Every station needs a 
dummy load just for this sort of testing.

73s and thanks,
Dave
NK7Z
https://www.nk7z.net


> On 2/24/2018 12:42 AM, Chris Hallinan wrote:
>> 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.
>>
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