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

[Greg]

I hate to say this but cable experts does not have a stellar record with
their installed connectors.  I would cut them off and install new ones.

73
Greg
 On Jun 4, 2012 10:55 AM, "Rick Johnson" <w3bi.rick at hotmail.com> wrote:

> Jump back down to Ron's input.
> I had that exact same scenario with my OCFD.  As soon as I transmitted
> any length of time on CW above 250W the SWR would jump up and the
> KPA500 would fault.
> The problem was a too small torroid 4:1 balun.  I bought a 5KW balun
> from Hy Power Antennas and the problem went away.
> Just because the balun is rated to 5KW doesn't mean you have to use
> that much power.
>
> 73,
> Rick W3BI
>
> -----Original Message-----
> From: mikefurrey at att.net
> Sent: Monday, June 04, 2012 1:47 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down
>
> 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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