Posted by
Don Ehrlich-2 on
Dec 28, 2004; 5:36pm
URL: http://elecraft.85.s1.nabble.com/KPA100-80m-poor-quality-SSB-tp372990p372991.html
Stewart,
I have been in contact with Gary intermittantly since first coming across
this problem in October. He assures me that Elecraft is working on a
solution and will have something to say soon. Both the "12 pF" fix and the
"1000 ohm resistor" fix have proved effective but are probably not the most
elegant or foolproof ways of solving the problem. For instance, the 1000
ohm resistor alters the reverse bias on D14 in a way that makes the T/R
switch marginal at high power levels. I suspect that Elecraft is taking
their time and checking out all of the possible effects of design changes
and mods before committing to a final solution.
We will just have to be patient.
Don K7FJ
The guests having departed - the Turkey finally disposed of - the booze
consumed
- thoughts turned to "Playing radio".
I have been getting reports on 80m that my SSB signal had some "edge" to it.
At first I put it down to RF feedback, but that was not the problem.
I used my FT1000MP to listen to the 2nd harmonic of the 80m signal.
Having read recent mails I first monitored the 3.5MHz signal and found the
"Buzz" that others had reported.
I then tried the following frequencies on 80 and noticed that as I increased
the
power control on the K2 the power output would suddenly jump, then when the
control was turned ACW the power would reduce smoothly and then suddenly
drop.
It was also observable on the FT1000MP S-meter, accompanied by a click.
It was like a form of hysteresis. All other bands gave smooth power control.
The results were as follows:-
3.8MHz Low point=20W High point=70W Hysteresis=50W
3.7MHz Low point=25W High point=70W Hysteresis=45W
3.6MHz Low point=35W High point=70W Hysteresis=35W
3.5MHz Low point=40W High point=70W Hysteresis=30W
Very unsatisfactory...
I substituted a 1k resistor for RFC3, and all the 80m problems went away.
Smooth power control on all bands and a better SSB signal on 80m.
Many thanks to those who found/cured this problem that first showed itself
on
CW, I would certainly have spent a lot of time tracking this one down !
I would suggest that owners of K2/100's check to see that their rig does not
exhibit these symptoms as it can make quite a big difference to transmitted
signal quality.
I, like a previous correspondent think that Elecraft should make some
comment on
this design problem, and it's solution.
73
Stewart G3RXQ
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