[RFI] SOLUTION - Keyboard Susceptibility (Sort of)

Michael Tope W4EF at dellroy.com
Sat Aug 11 21:41:18 EDT 2007

I found a solution (or at least a clue to the solution) for my 
keyboard RFI problem. In my shop I found an old AT style 
keyboard laying in the corner (complete with the large AT 
style DIN connector). I figured since it was free, I'd give it 
a try. Well, as it turns out, it wasn't really free since I had to
go to ratshack and spend $12 on an AT to PS2 plug adapter.

This old clunker did the trick, however. It isn't susceptible to 
RF even when I am banging away at 1500 watts RF output on 
160 meters. Unfortunately, this thing is so old and clunky that
its very hard to type with (it has a very hard action and the 
left control key bottoms out and stays there when you press
it - doh!). 

Still it was worthwhile spending the $12 for the AT to PS2 
adapter. Here's why: I took the old AT keyboard apart and 
discovered immediately why it performs better in the presence
of RFI. The two flexible circuit sheets that form the array  of 
membrane switches are laying right on top of a piece of steel
and the metal foil shield of the cable is grounded directly to 
the this steel ground plane. In contrast, the cheap PS2 style 
keyboard that folds at 300 watts has no ground plane under 
the row and column membranes and the keyboard cable is not 
shielded at all. 

BTW, I found the part number of the allegedly RFI proof 
keyboard that MFJ sells:


That's one possible solution. The other possible solution is
to give a wireless keyboard a try. I'll likely go with one of these
two alternatives. 

Thanks to everyone for all the suggestions. 

73, Mike W4EF............................................

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