[GreenKeys] Electrically Noisy Model 15 KSR

[ad7i]

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 at 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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