Posted by
Geoffrey Mackenzie-Kennedy-2 on
Jun 24, 2005; 1:44pm
URL: http://elecraft.85.s1.nabble.com/KPA100-power-on-20m-30m-update-tp379639p379650.html
Hello Ted,
At the risk of continuing this thread for too long, brief comment. IMHO you
hit on the main culprit causing problems on 20m / 30m - the inductance of
R19 and R20 as supplied.
If you like, I can go off list to discuss with you your other comments. I am
not surprised that you could not find evidence of other resonances, but
there are ways to expose them and they are an important part of a designer's
'toolkit'. The important thing is that your problem has been solved.
73,
Geoff
GM4ESD
----- Original Message -----
From: "Ted Turk" <
[hidden email]>
To: <
[hidden email]>
Sent: Friday, June 24, 2005 7:17 AM
Subject: Re: [Elecraft] KPA100 power on 20m/30m, update
> Geoff, Don,
>
> As an ex sufferer of this disease, my 2p worth.
>
> My investigations, admittedly only with the limited kit available to me
> including 20MHz scope and 2 or 3 different wattmeters, I think it was,
> showed that the output across all the bands up to 21MHz was remarkably
> constant for a given Q1,2 base voltage (and attempt at current
> calculation). However, there was a very marked voltage (estimated
> current) loss across the base drive circuits on the affected bands
> (C80,81/R19,20). Readings prior to this in the RF line merely
> confirmed the high drive requirement as did the Hi Cur on 20/30m. With
> much help and advice from guys at my club, we too considered the
> possibility of other spurious resonant circuits but could find no
> evidence for these in my kit at a level that affected performance.
>
> 73,
> Ted G7BQM K2#4732 and first year RF engineering student!
>
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