Hi Carel,
There's an ancient article in the February 1962 issue of 73 Magazine, pp
12-19, that covers this topic in depth.
If you can't run down an on line copy, I can have it scanned for you.
73 & Good morning,
Marv WC6W
http://qsl.net/wc6w/
--- On Sat, 11/10/12, Carel, pc5m <pc5m@xs4all.nl> wrote:
> From: Carel, pc5m <pc5m@xs4all.nl>
> Subject: [Amps] low Q output matching
> To: "'AMPS'" <amps@contesting.com>
> Date: Saturday, November 10, 2012, 7:26 AM
> Hi, I was wondering what else,
> besides bad harmonic suppression, will happen
> when I design my (single band) output matching network
> (PI-L) with low Q
> (lowest Q needed to get the match done) ?
>
> When using low Q design I will get
> - much smaller (variable) capacitors, especially for the
> bigger load C, so
> easier to get components
> - broader no-tune range
> -smaller RF stress on the components
>
> As an example for a 160mtrs amp, with Rload of 1700Ohm and
> intermediate
> impedance around 330Ohm:
> With Q of 10:
> CLoad =1200pF
> L-l=10uH
> Ctune=293pF
> Lpi=33uH
>
>
>
> With lowest Q:
>
> CLoad=400pF
> L-l=10uH
> Ctune=132pF
> Lpi=33uH
>
>
>
> When you plot both matching networks in a Smith
> diagram you see immediate
> the difference. Low Q is much more straightforward.
> To get the needed harmonic suppression a lowpass filter with
> fixed
> components is easy to construct (first harmonic at 3,8MHz
> needs 25dB and
> second one 20dB to get the same values as higher Q design).
> But maybe I have
> overlooked something . Thanks for your ideas
> 73's Carel, pc5m
>
>
>
>
>
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