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

Posted by Ken Cannaday on Aug 27, 2010; 3:42pm
URL: http://elecraft.85.s1.nabble.com/K2-KPA-100-excessive-power-issue-SSB-mode-some-bands-tp5470018.html

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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