[Elecraft] KPA100 power on 20m/30m, update

[Geoffrey Mackenzie-Kennedy]

Hello Don,

Yes I understand the purpose of the RC compensation circuit in the drive
path to each transistor to offset their decreasing gain as the working
frequency increases, and which cannot be fully dealt with by the RCL network
in the primary circuit of T1. As you say say they are not intentional traps,
which is why I use the term "spurious resonant circuits".  The possibility
of unwanted resonances in the feedback networks eg R39, C59, R35 is very
real. If for example R39 and C59 were to be a series resonant circuit at X
MHz,  the in-circuit gain of Q2 would decrease at X MHz.

RF design is an unforgiving mistress!!

73,
Geoff
GM4ESD


----- Original Message ----- 
From: "W3FPR - Don Wilhelm" <w3fpr at earthlink.net>
To: "Geoffrey Mackenzie-Kennedy" <gmk at gm4esd.fsworld.co.uk>
Cc: "Elecraft Discussion List" <elecraft at mailman.qth.net>
Sent: Thursday, June 23, 2005 9:58 PM
Subject: RE: [Elecraft] KPA100 power on 20m/30m, update


> Geoff,
>
> These are not intentional traps, but are a parallel RC circuit to adjust
the
> base drive with frequency (at low frequencies, the resistors are the main
> path, at higher frequencies, the capacitors pass more RF).  This is done
to
> compensate for the gain vs. frequency characteristics of the transistors.
> The inductance of the resistors is just an unfortunate by-product (but
must
> be considered just the same in the design).
>
> 73,
> Don W3FPR
>