At 22:55 02/11/2006, Mike Harris wrote:
G'day,
I have now done the resistor mod to no effect and will probably revert
'cos I don't like how I had to add the 1K0 in series with the base of Q1.
Hi Mike,
ISTR making the ALC *very* much more aggressive to tackle this,
especially on 80m. I think I cut the track to include a resistor to
the Q1 base and changed another resistor. I can't remember the
details (such as the values I ended up using) since it was more than
a year ago that I was experimenting with this. When I next get a
chance, I'll open up my K2 to refresh my memory.
Since I made those changes, I don't see any significant difference in
SSB output levels between bands and it's reasonably well tamed. I do
find the peak RF on SSB higher than the keyed RF level on CW, but
that applies to all bands. I've just got used to turning the
requested power control down a bit to keep within the 400W UK legal
limit with the K2 driving an Acom 1000, so it's not really been a
problem. You might want to experiment with more aggressive ALC around
the Q1 base on the KSB2 to see if you can tame it.
BTW, I have never seen a good explanation that includes an overview
of the firmware's part in the ALC control. There appear to be two
separate control loops here. With the later firmware changes to the
main PIC, one of those control loops only appears to be active in ALC
meter mode. With earlier (pre KPA100) firmware versions, it would
apply in RF meter mode, albeit being polled much less frequently, and
in ALC meter mode with very frequent AUXBUS operation. I had found
that by monitoring the AUXBUS with a scope in both modes and both
firmware versions. Elecraft were unaware of this difference but Wayne
was too busy to respond in detail at the time. The other control loop
is based on RFDET being fed back and compared with a DAC level using
the PIC on the KSB2. This seems to be an area of the K2 design that
would be good to have a decent explanation of including a summary
pseudo-code algorithm of what the firmware is doing to control the
ALC. I have yet to see a detailed description how BOTH of these
control loops work, so if anyone has any more details on this, I'd
appreciate the wisdom being shared :-)
Good luck,
73, David M0DHO
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