Thanks for the feedback Bill, and to Gary for the solution. Jack's
measurements were done on a very recent K2/100, so his rig may already
have the mod. If so, the SSB picture on my website would be the "fixed"
version. The overshoot on that picture is not excessive. All rigs
exhibit a little bit of this I'm sure.
Larry N8LP
William Shappley wrote:
Trevor -
I also saw this problem. I first saw it while checking out my new
KPA-100 on my Bird wattmeter - the Bird would see the overshoot
even when not in peak hold mode. I also have an LP-100, which
indicated the overshoot, but in my case it was not related
to the LP-100s fast response. Even the old slow Bird saw it.
My solution came from Steve Kavanagh, and he got it from Gary Surrency
at Elecraft. Here is a snip of the thread:
-SNIP-
Thanks to advice from M0DHO, LA3ZA and Gary Surrency
at Elecraft the problem described in
http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-12/msg00408.html
is now solved, or nearly so. I still see a big jump
in SSB power between 10 and 11 watt settings, but the
power output is always under control (no power supply
buzzing and RF metering does not read 100 W peaks when
set for 11 W, for example). No obvious signs of
splatter or distortion any more.
I put a 1k resistor in series with the base of Q1 in
the KSB2 and put 3.3k in parallel with R9. It's
pretty fiddly work on this compact board, but doable.
This is in the middle of the range for R9 suggested by
Gary Surrency. Probably I should go for the low end
of the suggested range (even more aggressive ALC).
73,
Steve VE3SMA
- SNIP -
In my case, I used the 1K and 3.3K values suggested, and it fixed the problem.
Mine was also much
worse on 40M than anywhere else.
Of course, the usual advice of checking everything in the ALC circuit
for bad solder or the wrong components
still applies. I had already gone that route without results when
Steve updated me. Note that the information
originally came from Gary Surrency at Elecraft.
I hope this helps.
73,
Bill
K4DXU
Trevor Smithers wrote:
I have just installed a recently constructed KPA100 (including the
latest upgrades)
and appear to have run into the erratic power control problem.
Using Tune + Display and an external LP100 meter, if I request 5w I
get 5w out.
Increasing power to 11w so as to engage the pa I also get 11w out -
so all seems
fine.
Switching to SSB, and speaking steadily into the mic, at a requested
5w I get
approximately 5-7w out on each band.
However increasing the power to 11w I get the following:
80m Req 11 Get 45
40m Req 11 Get 80
20m Req 11 Get 25
15m Req 11 Get 30
10m Req 11 Get 20
Reading back through the archive I see that others have encountered
the same
problem but cannot see a definitive answer to the problem. Anyone
have any
thoughts as to where to start looking.
73 to all
Trevor G0KTN
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