[Elecraft] K3 - bad CW note

[Don Ehrlich]

Interesting problem.  It would be helpful if you told us more about 
operating mode, band, type of antenna, etc and, most important, a complete 
list of the things you have already tried.  I'm sure you have already ruled 
out the usual culprits (power supply, rf in the microphone or keying 
circuit, etc).   The fact that you have problems at KH6LC but not at home 
and that the problem in independent of power level makes this problem unique 
in my experience.  It would be very interesting to know if the problem 
occurs on all bands or not.  Is there something else different at the KH6 
location such as microphone or keyer .. even antenna tuner?

Don K7FJ


>I have K3 SN 469, a kit K3-100 with transverter interface, tuner,
> several filters, and a recently added subreceiver.  It's updated with
> the latest beta firmware.
>
> This K3 works well at home, but I am having some trouble using it at
> the KH6LC station.  Those of you who operated the Cal QSO Party and
> worked KH6LC heard my K3, and it is bad signal reports from this
> operation (Thanks AF6EV!) that prompt this message.  The bottom line
> is that when the K3 is connected to the antenna at KH6LC there is a
> significant modulation of the output amplitude, synchronous with the
> power line, and independent of power level.  It seems to be a buzz
> (square wave) rather than a hum (sine wave).  Replacing the antenna
> connection with a dummy load removes the buzz.  Turning the TX AGC off
> has no effect.  The K3 is grounded to the station ground bus via the
> rear panel ground screw. There is some evidence that simply connecting
> a long coaxial cable (from the radio room to the garage at KH6LC)
> terminated in a dummy load can introduce the buzz.
>
> So what, you say, there's a ground loop and when you find it you'll be
> fine.  Well, Ken N6KB and I have spent a fair mount of effort on just
> that and so far we have come up empty handed. In the interest of
> brevity I won't list all the things we tried. The reason why this
> might be interesting to K3 owners is that no other radio that we have
> tried seems to be affected by whatever condition is causing the
> problem.
>
> So I wonder if there is an assembly error that might be a contributing
> factor.  What I'm looking for is some internal part that should be
> grounded but isn't, or vice versa.  Before I dig into it I'm hoping
> that those of you with more K3 experience than I have can suggest a
> place to look.  In the meanwhile, we are going to try for symptomatic
> relief by using isolation transformers, etc.
>
> Curt AH6RE