[RTTY] Optoisolator problem

[Glenn VanBlaricum, W6KNB]

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)