[RTTY] Optoisolator problem

[Jerry Flanders]

If you have a different opto, try that. Or try reducing the resistance. The 
opto will switch more reliably then. I had a problem like this one time and 
reducing the resistance to increase the opto's LED current helped. Don't 
know about the RFI.

Jerry W4UK

At 09:35 PM 2/8/2002 +0000, Glenn VanBlaricum, W6KNB wrote:
>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