K2 problem with tracking ALC on 40m

   Hello,

   i  finished my K2 / KPA 100 including SSB and DSP build last week. The
   build  was  done  without  problems and i am on air. During my tests i
   found one strange thing on 40 m SSB operation.

   Someone  told  me  my  audio  is  not  okay. I recognized : On 40m SSB
   operation  the  output  of  the PA is much higher on normal modulation
   level,  when  i  compare it to other bands. I turned on ALC meter to
   check the the level. ALC was very high. After a short moment the level
   was  adjusted  automaticlly, like described in the documentation. I am
   surprised, why is it adjusted when ALC meter is enabled only ? After
   switch  back  to RF meter, the output is like on the other bands. If i
   switch  to  another  band and go back to 40m the problem is back again
   until i enable my ALC meter.

   Is this a known problem ? Any hints where i can investigate ?

   73 de Joerg (DL3QQ)
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[Paul Saville-4]

Hello Joerg,

Yes this is a known problem. After some correspondence with
Gary at Elecraft Support about 6 months ago, we concluded
that it is caused by a software bug in the KSB2 firmware.
The work-around is to leave the meter in ALC mode, which is
what I do. I have seen no other mention of this problem on
the list, which puzzles me.

73 Paul ZL3IN

> Is this a known problem?
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[David Honey]

At 19:45 12/10/2005, [hidden email] wrote:
>    Someone  told  me  my  audio  is  not  okay. I recognized : On 40m SSB
>    operation  the  output  of  the PA is much higher on normal modulation
>    level,  when  i  compare it to other bands. I turned on ALC meter to
>    check the the level. ALC was very high. After a short moment the level
>    was  adjusted  automaticlly, like described in the documentation. I am
>    surprised, why is it adjusted when ALC meter is enabled only ? After
>    switch  back  to RF meter, the output is like on the other bands. If i
>    switch  to  another  band and go back to 40m the problem is back again
>    until i enable my ALC meter.

Hi Joerg,

I suffered the same type of symptoms on 80m. The transmit audio was OK, but
with the
power control set anywhere from 11W upwards, I would always get 100W.
I also found changed behaviour between the main control board firmware
revisions.
Prior to 2.04, I saw that even in RF meter mode, it was monitoring RFdet and
actively sending auxbus signals to the KSB2. With 2.04, that did not happen
unless you were in ALC meter mode. This was an undocumented change.
Until I pointed out to the support folks, they were unaware of this change.
In ALC meter mode, the ALC control was much better. I never did get a response
back from Eric on whether this was an intended change or a defect.

The cure was to make the ALC in the KSB2 more aggressive. It was getting
a lot of drive, and with the high gain of the KPA100 at 80m, it was too much
for the ALC to control. ISTR having to cut a track on the KSB2, install an
additional resistor and change the value of another resistor. Sadly, the
computer
where I had details of this has developed a motherboard fault and although
I have
backups and the disks will be OK, I can't get at the details and can't remember
accurately the changes I made. Gary at Elecraft will be able to give you
the details.
I made mine even more aggressive than Gary suggested since I seem to have quite
high drive and KPA100 gain. I've had good audio reports with those settings
while
driving a linear.

One thing I have consistently noticed is that the peak RF power on SSB is
always
about 50% higher than the requested power when the power control is below about
70W. On CW, there's a close match. It's almost as if their is a calibration
problem
only affecting SSB. Given the gain of my linear on 80m, it means I have to
keep the
requested power between about 11W and 15W to limit the KPA100 power out
to limit the linear to 400W UK legal limit. As you go on the higher bands, this
is less of a problem.

73, David M0DHO.

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