Posted by
Chris Hallinan on
Feb 24, 2018; 1:36pm
URL: http://elecraft.85.s1.nabble.com/KPA500-Faulting-on-high-SWR-on-power-rise-tp7638486p7638493.html
Thanks, everyone for the helpful hints. Some additional information:
This installation is brand new. The antenna has been up only a month or
so. Tuner and Balun even less. Coax is newly run, and I've deliberately
avoided sharp bends. I purchased the KPA500 in December, so all of this
QRO is new for me (in this century at least!)
I am running through a surge protectors from Alpha Delta. I will double
check is is not the 200W versions! Hmmm, now that I think of it, maybe
that's it??? Will check after coffee!
Any tips on how I would detect/locate any potential arcing?
I do understand the nature of the antenna and the potential wide range of
impedances possible with this multi-band setup.
-
I'm going to scan it at the balun this morning with my AIM 4300 for
starters. Oh, and check/bypass the surge protector too!
Thanks again,
73 de K1AY
Chris
On Sat, Feb 24, 2018 at 7:44 AM, Victor Rosenthal 4X6GP <
[hidden email]
> wrote:
> Just to add to all the possibilities, there could be an arc at the balun.
> Most authorities suggest a 1:1 balun with a setup like this. As you know,
> the impedance seen at the balun will vary all over the map, depending on
> the band and the length of the 600-ohm line.
>
> I've calculated that the voltage that appears at that point in my somewhat
> similar setup is as high as 7 kV when I'm running 1200 watts on one
> particular band. A 1:1 balun designed for tuner use (e.g., one like this:
> <
https://www.dxengineering.com/parts/dxe-bal050h10at> or this:
> <
https://www.dxengineering.com/parts/dxe-bal050h11ct>
> would be suitable.
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> Formerly K2VCO
>
http://www.qsl.net/k2vco/>
> On 24 Feb 2018 07:42, 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.
>>
>> 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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