I like the idea of an external tuner with some harmonic rejection.
It sounds like the high power PA's need to see a broadband 50 Ohm match. We
might consider a weak diplexor that transfers power on the operating
frequency and dumps power to a terminator above (and below?) frequency. It
might take fewer expensive components to get -10 dB return loss than to
get -30 dB harmonic attenuation.
It also might make sense to have several 'plexed ports on the back for
different bands. Relays would either connect an internal terminator or the
antenna. I've got separate feedlines for each band...but installations
vary.
I assume that the amp only needs a match where it has frequencies with some
energy...such as higher harmonics? So the diplexor need to pass low
frequencies and dump high frequencies to a termination, no?
jeff, wa1hco
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Phil Clements" <philk5pc@tyler.net>; "Dan Levin" <djl@andlev.com>;
<amps@contesting.com>; "Pete Smith" <n4zr@contesting.com>
Sent: Thursday, March 06, 2003 6:15 AM
Subject: Re: [Amps] MRF150 based 1500 watt amp design/cost
> > As long as we're just designing this thing on paper, why wouldn't it
make
> > sense to design for a 50-ohm output impedance, forget the low pass
> filters,
> > and instead include a low-pass-type autotuner permanently in line as
part
> > of the amplifier? Isn't this essentially what Acom does in the 2000A,
> > although with tubes?
>
> Solid state amps do not like high Q networks located very near the output
> devices. Best to have a multi-section low-Q filter and then put the high-Q
> stuff after that, and hopefully through some lossy transmission line to
> limit the mistermination, or waste some power through intentional loss at
> the output.
>
> 73 Tom
>
>
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