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 <[email protected]>
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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