Recently I noticed some odd behaviour of the K2/K60XV driving a DEMI 2m
transverter and an amp. Switching on and off my rotor control box or the
AC-powered fan for the amp caused the K2 to do the following: (1)
receiver muted for about 1 second, (2) S-meter read S9+40 dB for the same
time and (3) the transverter key line (K60XV J2 Pin 2) went to ground
("transmit") for the same time.
I could eliminate this behaviour by unplugging everything from the XVTR
OUT jack, identifying this as the pickup location for the switching
transients.
I could also eliminate it by putting lots of clip-on ferrite beads on the AC
power cord of the rotor control box or fan switch, confirming that the coupling
was at RF (HF or low VHF). One bead had little effect, so the coupling was not
at UHF.
I could also eliminate it by removing my external 28 MHz bandpass filter from
the TX line from the K2 XVTR OUT to the transverter. The shield of the coax on
the K2 side of this filter is terminated to the metal box INSIDE the box....so
it isn't quite perfectly shielded.
With just a short piece of coax with phono plugs on each end plugged into
the XVTR OUT jack the behaviour was there. Insulating the pin of the
unconnected plug and then covering the whole plug with aluminum foil to shield
it eliminated the effect. So all it took was a half inch long
antenna to pick up enough switching transient to make the K2 do weird
things ! It's no wonder some of us have had trouble with 6m etc. getting into
the XVTR OUT via the XV222, etc. !
I was also able to make the K2 switch in the same way simply by touching
a 1 ft long alligator clip lead to the exposed pin of the phono plug...no
actual signal was being switched at all. This was at a rural location with no
local transmitters except possibly the "smart" electrical meter
at 915 MHz. It seems very sensitive.
I did confirm (by unplugging the K60XV from the main board and making
ohmmeter measurements) that there is contact between the shield side of
the XVTR OUT jack to the case of the K2.
All this made me wonder if the 8R (or the 6T) line on the K60XV board
might be used to inhibit the RF detector in receive mode to stop this all
from happening. But I haven't made any real progress on this - I think I
might rather have advice from Elecraft on how to do this if they were so
inclined as to want to think about it.
Comments ? Can anyone reproduce anything similar ?
73,
Steve VE3SMA
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