RE: KPA100 power on 20m/30m, update
Posted by
Don Wilhelm-3 on
Jun 23, 2005; 9:58pm
URL: http://elecraft.85.s1.nabble.com/KPA100-power-on-20m-30m-update-tp379639p379647.html
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
> -----Original Message-----
>
> The "Trap theory" makes a lot of sense, and Don's comment about low
> tolerance C80 and C81 capacitors would seem to support it. But if the
> resistors in parallel with C80 and C81 are the only "Inductors" that form
> the L part of the traps, I would have thought that by simply changing R19
> and R20 to so called Non Inductive types would cure the 30/20
> meter problem.
> But this might just move the problem to a higher band because of the
> inductance of leads AND PCB traces between C80/R19 and between
> C81/R20. But
> are these the only "traps"? Consider the low Q notch C80/R34 and C81/R35.
>
>
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