Group,
I think I've discovered the cause: I noticed the SWR seen by the
K3 at 52.00MHz is 1.2:1, whereas it's 10:1 on all other bands. This
was shown on the K3 SWR meter and confirmed with my antenna analyser
at the K3 antenna connector. I did some detective work and
discovered that the length of the (short) jumper cables connecting the
K3, the sensor of my LP-100A and the dummy load was either having a
transformer effect or otherwise introducing stray reactance. The
results was a less than perfect 50 ohm match on 52.000MHz.
I changed the length of the jumper cables just a little (swapping
them out with others of different length), and the SWR seen by the
K3 came down to 1.0:1 @ 50Mhz and the Tx Gain calibration routine then
ran perfectly.
I'm using LMR-240 ultraflex jumpers and individually, connected to
the dummy load, they check out OK. It's something about the total
inter-connect length at 50Mhz.
Thinking back, I suspect I've changed the in-shack jumper
arrangements since the last calibration.
Thanks for everyone's help.
73,
John
VK7JB
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