[Elecraft] Keying Bandwidth Mod

[Masleid, Michael A.]

Hi Vic

>I wonder if replacing the bottom plate with a steel one (it wouldn't be =

>too hard to make) would help?

I tried that, but it didn't seem to do much good.  I think you need to
build a complete steel cage.

I think the best fix is to get rid of the current loop in the K2 that is
causing the problem.  I'm guessing that the core in L30 concentrates the =
60 Hz
field though the L30 windings, and generates a 60 Hz voltage that =
modulates
the capacitance on D23 and D24 - and whatever else the relays click in.

I thought T5 should short out any voltage produced this way, but perhaps
not, since L30's impedance is not that much larger than T5's at 60 Hz.

A simple fix might be to put a 0.1 microfarad capacitor in series with =
L30.
I haven't looked at the board to see if there's a clean way to do that.
The capacitor has a huge impedance at 60 Hz compared to T5 - but =
shouldn't
cause any problem at VFO operating frequency.  No hum on T5, no hum on =
the
varactors.

I don't know if this would actually work though.  I do know that the K2
goes crazy if you inject a 60 Hz magnetic field into L30. =20

The scientific way to test this is to build a big 60 Hz Helmholtz coil, =
put
the K2 into the uniform field and look at FM deviation.  I need a bigger
work bench...

73, de Michael, AB9GV=20