Re: KPA100 - 80m poor quality SSB
Posted by
Stewart Baker on
Dec 28, 2004; 6:11pm
URL: http://elecraft.85.s1.nabble.com/KPA100-80m-poor-quality-SSB-tp372990p372992.html
On Tue, 28 Dec 2004 09:36:00 -0800, Don wrote:
> 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
Thanks for the "Heads up" Don.
I will look forward to the official modification when it is released.
73
Stewart G3RXQ
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