[Elecraft] Strange KPA500 problem on 6M

[Carl Yaffey]

Wow. That was a great job of problem solving. In my case, I get the KPA fault with just 8 watts of drive from the K3S. So I doubt that’s my issue.

Carl Yaffey K8NU
Recording studio.
cyaffeyNO_SPAM at gmail.com
614 268 6353, Columbus OH
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On Dec 5, 2016, 2:07 PM -0500, David Olean <K1WHS at metrocast.net>, wrote:
> Last summer a friend of mine got a new K3s and had problems with it on
> just six meters. As soon as he raised power above about 10 watts, the
> SWR reading went crazy and the rig gave high VSWR warnings. He checked
> his six meter yagi with another SWR analyzer and the antenna checked
> good. After goofing around with it and getting nowhere, he brought it
> over to my place and we tried it on my six meter array. We saw the same
> problem here, high VSWR, but with different combinations of antennas,
> the K3s actually worked OK. It also worked fine into a dummy load. I
> got suspicious and tested the K3s with a spectrum analyzer. Sure enough
> the rig had a huge parasitic oscillation on about 27.4 MHz and with most
> of the power there, you could see how the radio would show a high SWR.
> It only appeared when the internal 100w PA kicked in. He did not have a
> KPA-500. This was just a K3s.
>
> He sent the K3s back to the factory along with some pictures of the HP
> spectrum analyzer screen. I am not sure if they duplicated the problem
> at the factory, but they applied a few changes to the PA and now it is
> all OK. If the K3s was to have an unwanted oscillation, it would sure
> mess up the KPA-500 and show high VSWR and maybe damage some filter
> components. If all else fails, that may be a place to look.
>
> Dave K1WHS
>
>
> >
> >
> > On 12/4/2016 6:30 AM, Mike va3mw wrote:
> > > As quoted
> > >
> > > If the amp works on a dummy load, then look beyond the amp at this
> > > time until you have eliminated everything else.
> > >
> > > Somewhere else you are getting a voltage breakdown that is arcing and
> > > tripping off the amp due to high swr. An MFJ analyzer will not show
> > > that.
> > >
> > > Mike va3mw
> > >
> > > > On Dec 4, 2016, at 12:54 AM, Jim Brown <jim at audiosystemsgroup.com
> > > > wrote:
> > > >
> > > > > On Sat,12/3/2016 9:41 PM, Vic Rosenthal wrote:
> > > > > Look at any cables, switches and connectors that are common to the
> > > > > various antennas.
> > > > Yes. Lots of "off-brand" coax is junk. So are most un-branded
> > > > connectors. If the PL29-style connector doesn't say Amphenol 83-1SP,
> > > > it's probably junk. How well is the connector soldered or crimped?
> > > > If crimped, was it done with the "official" crimper for the
> > > > "official" crimp connector that matches THAT specific coax? If not,
> > > > it's suspect.
> > > >
> > > > Are you using any of those shiny adapters that are sold at hamfests
> > > > for a few bucks? They're JUNK! Ask me how I know. :) They have
> > > > caused me many problems that were tricky to diagnose.
> > > >
> > > > IMO, the only GOOD coax connectors say "Amphenol" on them, or are
> > > > ancient MIL-spec parts with MIL numbers stamped into them. I snap up
> > > > stuff like this when I find it at ham flea markets.
> > > >
> > > > 73, Jim K9YC
> > > >
>
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