[Elecraft] Keying Bandwidth Mod

[Vic Rosenthal]

Masleid, Michael A. wrote:

> 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.  

Very interesting!  In my opinion, it's just too sensitive (especially if 
you have to move an amplifier 30 feet away to eliminate the effect).

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco