Re: K2 KPA/100 excessive power issue, SSB mode, some bands

Posted by Bob Naumann W5OV on Aug 27, 2010; 4:28pm
URL: http://elecraft.85.s1.nabble.com/K2-KPA-100-excessive-power-issue-SSB-mode-some-bands-tp5470018p5470182.html

Have you tried a different power supply?

I have seen many power supplies that are sensitive to 40m RF and trip out
as you describe.

Since you already know you have 40m RF in the shack, perhaps this is a
much simpler problem to resolve?

73,

W5OV

> I had an RF feedback problem on 40 meter SSB, which I brought under
> control,
> mainly by winding a foot or two of mike cable through a ferrite core.
>
> However, I had been having another problem on 40 meters SSB that had gone
> unnoticed until the power supply (rated at 30 amp surge) tripped out on a
> voice peak.
> Power control seemed okay because the output as measured on the meter in
> my
> MFJ tuner was the same as the power setting on the K2 in Tune, Tune +
> Display (override 20 watt limit), and CW modes.
>
> However, on SSB, the circumsatance was very different.  If the setting was
> for 100 watts, the meter in the tuner would often kick up to 100 watts or
> more on voice peaks, whereas with my Icom transceivers, it generally will
> not kick
> any higher than half the power setting (i.e. 50 watts).  (I really have no
> good way of accurately measuring peak power on SSB and always assumed PEP
> would be the same as the output in continuous carrier mode.)  Turns out
> that
> on 40
> and 30 meters, and to a lesser extent on 80, while transmitting into a
> dummy
> load, I apparently get two to four times the expected power on voice
> peaks, judging by the meter in the tuner (and applying the times two
> formula).  This only occurs when the KPA/100 is active.  It does not occur
> with the basic K2 in QRP mode.  Moreover, even with KPA/100 active, if I
> set
> compression (SSBC) and audio (SSBA) to the lowest levels, the power
> reading
> levels appear to be similar to the Icom - about 50% of nominal power on
> voice peaks.
>
> My KPA/100 is revision C and does not have the KPA100UPKT installed.  Does
> anyone have any suggestions for this problem?  Would the KPA100UPKT likely
> solve the problem?  On the other hand, would there be any harm in setting
> the
> power levels and/or the SSBA and SSBC parameters so that output does not
> exceed
> 100 watts, and continuing to operate with the KPA100 as is?
>
> Any help would be greatly appreciated!
>
> Ken, W4NZC
>
> 73!
>
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