You mentioned RFI from the keyboard. Is the RFI problem more consistent with the keyboard or the selector magnets? To confirm it's the keyboard and not the magnets, temporarily put a shorting jumper across the selector magnet terminals and see if the RFI is still present when the keyboard is operated.

For the keyboard contacts, try a 1000pF @ 400 volt cap across the keyboard contacts for RFI suppression.

For the magnets try a snubber as electrically close to the magnets as possible (on the magnet terminals is best). Add a 1000 pF 400V cap across the magnets. That should kill (or reduce) the RFI as it limits dV/dt when the loop opens. You might also add a series combination of 470 ohm resistor (1/4 watt is fine) and 0.1uF @ 400 volts across the magnets. The 0.1uF/470 ohms limits the voltage of the ringing of the R-L-C circuit when the loop opens.

Paul, ad7i

On Sat, Nov 13, 2021 at 12:19 PM JOHN MCCARTY <n9hrt@sbcglobal.net> wrote:

Keepers of the green keys;

I have a model 15 KSR that used to be in a private home for TTD service. I got it off Craig's list some time back.
We use the machine as a demo unit at events and it works well. The crowds are always drawn to it. Here in Chicago we
have a 2 meter FM channel we run these on. The problem is we usually have other radios running at these events and
when the keyboard is in use it really rips up 20 meters. I ran a test using just one of my stations RX's and it was
far worse on 20 that 80 or 10 meters.

Is there somewhere I can hang a cap or two and quite things down a bit?

Thanks for your help

John n9hrt
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