[Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

[mikefurrey at att.net]

My bet will be on a bad connection someplace after the amp. With power 
something is shorting ... could be in coax connector, antenna, etc ... been 
through that. Once had found an elevated radial on 160 inverted "L"  had 
dropped and touching a tree limb was the problem.

73, Mike

-----Original Message----- 
From: Ron D'Eau Claire
Sent: Monday, June 04, 2012 12:33 PM
To: 'ai6ii' ; elecraft at mailman.qth.net
Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

Mark has an excellent point, especially if you have a ferrite core
transformer (balun, etc.) somewhere in the antenna system. One thing that
can cause that behavior is heating of the toroid core. At a certain
temperature, the core's magnetic properties change dramatically, changing
the inductance and so causing the SWR to change.

Ron AC7AC

-----Original Message-----

What happens when you run the KPA-500 into a dummy load? If all is well, I
would guess that something is changing under high power and affecting the
load.

-----Original Message-----
From: ai6ii <ai6ii at att.net>
To: elecraft at mailman.qth.net
Date: Mon, 4 Jun 2012 10:00:54 -0700 (PDT)
Subject: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down


I have installed a new antenna and have strange changing swr. When testing
with RigExperts meter I find good resonance at say 15m (21.200). With the
K3
at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I
bring the amp online and drive it at 200 watts, all is still good even with
a 15 second key down period. Driving the KPA500 to 275 watts, still okay
with key down, although the KPA500 meter now shows 1.1. BUT when I increase
the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500
shows REFL HI and drops into STBY.

And here is the kicker...NOT ALL THE TIME!

So I think it has to be in the coax. But the 75feet of RG213 is brand new
premade from Cable Xperts with the connectors.

I will try a different coax. Any other suggestions?

..mike

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