Re: SSB Power control and KPA100

[N8LP]

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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