FINALLY! The Gremlin has been slain! With K1MK here early for CQWW SSB we
started doing some more testing with him running the radio and me doing
stuff. We started with hosing down the feedlines and stuff outside. It did
raise the threshold from 50w to 100w or so in a couple steps, but nothing
dramatic. Then we started looking for higher harmonics again, we found an
odd one at 49MHz and got a null with the 6m antenna sideways at the shack.
We found one just above 2m, but couldn't get any bearing on it. Not having
a VHF-AM receiver I tried the HT that went above the band and could hear it
on FM in the shack. So loud that the rubber duck was too much... so switch
to the paperclip and scan the shack. Its the strongest around the 10m
station, mostly near the stubs, so disconnect those. I've been here before
so didn't really expect to find anything new... but kept disconnecting stuff
and the threshold kept going up and up, but wouldn't go away. It seemed to
be most sensitive to the SWR meter being in the circuit, yes some of you did
suggest those, but I had already disconnected all the meters from the
antennas and still had the subharmonic... so that just couldn't be it. Put
the meter in, 100w or less, take the meter out 1000w or more... but it
wouldn't go away. Put the meter in and pull the 12v supply to it, 1000w
threshold! Pull the power from the 80m meter, threshold goes up some more.
Pull the power from the 40m/SO2R pair of meters, and it goes up more. Pull
the 15m meter power and it goes over 1500w... pull the power from the 20m
and 160m meters just in case... SILENCE! I'll test more after CQWW SSB, but
my best guess is that something in the PEP circuit that gets 12v power was
rectifying and resonating with the coax stubs on the different stations... 7
sources, all in the shack! Well, I did get lots of ugly stuff cleaned up
outside anyway... maybe there were some other sources outside also... in any
case now we can have a nice quiet contest without QRM from ourselves anyway!
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
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