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

Posted by Don Wilhelm-4 on Aug 27, 2010; 4:00pm
URL: http://elecraft.85.s1.nabble.com/K2-KPA-100-excessive-power-issue-SSB-mode-some-bands-tp5470018p5470065.html

  Ken,

That description sounds suspiciously like you are developing a parasitic
on 40 meters.
Yes, the first step in getting that under control is to install the
KPA100UPKT.
It was developed specifically to address a problem very similar to yours.

There is another possibility (since you mentioned the SSBA and SSBC
parameters) - that you are driving the mic input too hard.  switch the
display to read ALC.  You should have no more than 3 bars with maybe an
occasional 4th.
There should be no problem with an SSBC setting of 3:1 or even 4:1, but
the SSBA parameter will depend on your mic.  If you are using the
Elecraft mics, set SSBA to 1.

73,
Don W3FPR

On 8/27/2010 11:42 AM, Ken Cannaday wrote:

> 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!
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html