Posted by
Elecraft mailing list on
Apr 01, 2017; 1:44pm
URL: http://elecraft.85.s1.nabble.com/Antenna-Problems-with-K3-firmware-5-57-tp7628786p7628808.html
This may not be directly related, but I had power indication problems in
that the SWR and FWD power readings on my K3 had become erratic with surging
of indicated power on CW from a setting of 50W up to 100W and over, yet a
constant tune signal was rock steady at 50W. I thought it was an
intermittent antenna problem, then switched to it being an SWR measurement
problem. I tried everything including two updates of firmware which had
temporary benefit but didn't last. Wrote to Elecraft and carried out all
checks they recommended except (to my embarrassment) for one which I thought
unlikely. There is a lesson here!! Yes, it did turn out to be the real
cause and that was to check and tighten the three screws on the bottom cover
for the LPA transistors (p63 in assembly manual).
My assumption now is therefore that loose mountings / grounding may have
been causing erratic reactive components in the LPA power circuitry leading
to sprogs which trigger the much improved VSWR sense circuitry to hunt but
never actually find a stable point except when on steady tune up carrier.
Incidentally it didn't show up when running low power (10W) using the LPA
only. It is so easy to jump to the wrong conclusions; in this case where
improvements in the SWR sense loop performance was masking the growing
problem with poor ground of key LPA components. After re-reading the
Elecraft advice again I did actually check the screws (they were very loose)
and tightened them up it all went back to normal. Disconnecting the cables
from the K3 to connect to the PC for the firmware uploads must have
temporarily disturbed the seating of the LPA screws giving a false and
temporary indication of a fix. A regular ragchew contact reported much
cleaner rf signal as seen on a pan display after the repair.
Dick G3WRJ
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