As usual, a few hours before a rtty contest, I'm trying once again to solve
an RFI problem.
I've been using identical resistor/transistor circuits to key both the PTT
and data line to my FT-1000. On 40 meters at power levels above about 200
W, the circuits lock on until I dial down the power. This doesn't occur on
other bands.
I thought I would try optoisolator circuits instead, so I wired up a 4N25
with an input line 1.2 k resistor only to discover that while it seems to
switch state when the input is toggled, the resistance in the output
collector-emitter is too high to switch my transceiver. I measure about 40
ohms in the "on" state for the optoisolator, but the transistor circuit
shows only about 3 ohms and works fine with the transceiver. I tried 4N33
optoisolators with the exact same results.
Has anyone experienced similar problems and found a solution? Obviously the
real solution is fixing the 40-meter RFI, but the antenna match is pretty
good, I have the coax coiled near the rig, and I have ferrites on every
line in sight. Any ideas?
Good luck to all in the WPX later. I'll be there, just with not much poop
on 40 meters.
Glenn W6KNB (putting the rare W6 prefix on the air)
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