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KPA500 - Not Going To Full Power

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fyredude901

KPA500 - Not Going To Full Power

Received my KPA 500 / KAT500 combo for Christmas. Got them hooked up and
they were working like a charm and have for several days. I am mostly on
digital and will typically run around 300 watts out. I am using a Flexradio
6500 and my output on it is around 22 watts. Today, I pushed the output up
to around 27 (which drove the amp over 310 watts). At that time, the power
meter started surging (sorry, best way that I can think to describe it). It
amp never went above 310, but it was like the power was being cycled on and
off to the unit. The output was pulsing high and low. When I backed the
Flex back down to 22 watts, and the output of the amp was 300 or less, this
issue stopped. I am assuming it is the protection system for the amp.
Still, I would like to know what the possible cause of this likely is so
that I can troubleshoot and fix it. Any advice that can be provided would
be greatly appreciated!!

73
KD9EGK

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Bob McGraw - K4TAX

Re: KPA500 - Not Going To Full Power

First would seem that something in the antenna system is causing a
problem. I run my KPA500 & KAT500 at 450 to 550 watts out without any
issues. What's the antenna and feed line being used? What bands? Is
the output of the FLEX surging as well?

73

Bob, K4TAX

On 1/6/2019 3:36 PM, fyredude901 wrote:

> Received my KPA 500 / KAT500 combo for Christmas. Got them hooked up and
> they were working like a charm and have for several days. I am mostly on
> digital and will typically run around 300 watts out. I am using a Flexradio
> 6500 and my output on it is around 22 watts. Today, I pushed the output up
> to around 27 (which drove the amp over 310 watts). At that time, the power
> meter started surging (sorry, best way that I can think to describe it). It
> amp never went above 310, but it was like the power was being cycled on and
> off to the unit. The output was pulsing high and low. When I backed the
> Flex back down to 22 watts, and the output of the amp was 300 or less, this
> issue stopped. I am assuming it is the protection system for the amp.
> Still, I would like to know what the possible cause of this likely is so
> that I can troubleshoot and fix it. Any advice that can be provided would
> be greatly appreciated!!
>
> 73
> KD9EGK
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
> Elecraft mailing list
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Don Wilhelm

Re: KPA500 - Not Going To Full Power

In reply to this post by fyredude901

What happens if you use CW or a constant carrier.
Data modes throw the proverbial "wrench" into the works because there
are so many, each with different characteristics.

Test with CW mode or a constant keydown (for a reasonable time - 30
seconds or so) and see what happens.

If that condition happens with CW, then take the KAT500 out of the
situation and operate the KPA500 into a dummy load. Is it OK up to 500
watts or more? If OK, the KPA500 and your Flex is OK - focus on the KAT500.

Did you train the KAT500 to your antenna(s) while in AUTO mode, then
switch the KAT500 to MAN mode? If not try that. It may be that at
higher power, something in your antenna system is breaking down and the
KAT500 (if left in AUTO) is trying to tune, which will break the keying
line to the KPA500 if cabled correctly until the tune is completed.

My bet is on something is changing in your antenna system at higher
power - look for arc points, end insulators, and possible loose
connectors (PL-259 connectors should be just a bit more than finger
tight, use pliers lightly).

If you are using a balun, is it arcing inside? Did it gather a bit of
moisture inside? Are you exceeding its saturation point - a good
possibility if you are using a balun to transition to a parallel
feedline as might be the case with a commercial G5RV antenna.

The very best test is to establish what happens into a dummy load.

73,
Don W3FPR

73,
Don W3FPR

On 1/6/2019 4:36 PM, fyredude901 wrote:

fyredude901

Re: KPA500 - Not Going To Full Power

I think you may have hit it right off the bat. The KAT is in AUTO mode not
manual. Fingers crossed that works. Thanks!!

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fyredude901

Re: KPA500 - Not Going To Full Power

In reply to this post by Bob McGraw - K4TAX

Gap Titan antenna to 50 feet LMR 400 coax. Problem started on 40 then I
noticed on 20. FLEX output not surging. Thanks for your time and
assistance.

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Elecraft mailing list

Re: KPA500 - Not Going To Full Power

In reply to this post by fyredude901

Did you hear any clicks from the KPA when this was happening? Did the FAULT LED blink?

It sounds like the amplifier is experiencing an issue that requires it to start to protect itself.
It does this by switching in a 3db pad, which cuts the output power in half. If it sees no further
issues while the pad is engaged, it will switch out the pad. If the issue recurs, so will switching
in the pad. If the KPA is sensing a problem in its output, such as high reflected power, it will
protect itself exactly as you describe. This very well may be due to a problem in the antenna
system involving arcing or other issues as others have described. look for burn marks at the
antenna (most likely inside the connectors). We build our stations for low power operation, then
when we upgrade with an amplifier, we experience just these sort of issues with the antenna
system. It could be connectors, adapters or the antenna itself. In your case it sounds like you
may have a matching system at the antenna that is overheating due to high power and thus
changing the load presented to the ATU and amplifier. The KPA will see these sort of changes
faster than the KAT and thus it will react faster.

The advice is good - check the antenna system to make sure it is not being overloaded.

73!
Jack Brindle, W6FB
Elecraft Engineering

> On Jan 6, 2019, at 1:36 PM, fyredude901 <[hidden email]> wrote:
>
> Received my KPA 500 / KAT500 combo for Christmas. Got them hooked up and
> they were working like a charm and have for several days. I am mostly on
> digital and will typically run around 300 watts out. I am using a Flexradio
> 6500 and my output on it is around 22 watts. Today, I pushed the output up
> to around 27 (which drove the amp over 310 watts). At that time, the power
> meter started surging (sorry, best way that I can think to describe it). It
> amp never went above 310, but it was like the power was being cycled on and
> off to the unit. The output was pulsing high and low. When I backed the
> Flex back down to 22 watts, and the output of the amp was 300 or less, this
> issue stopped. I am assuming it is the protection system for the amp.
> Still, I would like to know what the possible cause of this likely is so
> that I can troubleshoot and fix it. Any advice that can be provided would
> be greatly appreciated!!
>
> 73
> KD9EGK
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]