----- Original Message -----
From: "Dan Sawyer" <dansawyer@earthlink.net>
To: "Amps" <Amps@contesting.com>
Sent: Monday, January 21, 2008 9:36 AM
Subject: [Amps] tuning bandpass filters
> All, I am trying to tune bandpass filters. I have a network analyzer and
> can see both reflected and transmitted signal. My questions are:
>
> If the filter were tuned and terminate properly in the bandpass range is
> the reflected signal a minimum?
The termination should be a broadband one and a pure resistance. A perfect
filter will have no reflection. In the real world you want at least a 20db
return loss in the passband.
Im making an assumption here based upon no input info and the name of the
forum that you want to drive a grounded grid linear amp. If so the common
matching device is a 3 pole pi network which is a low pass filter and not a
bandpass.
>
> Should the reflected signal show the same shape as the transfered signal?
I dont understand that. You are looking at a single trace on the NA that
will show the shape of the filter. Set your markers for the desired start
and stop frequencies.
>
> What is the best way to tune these filters?
So they work. (; The input tuning is adjusted for a match to the
transmission line once you do your cal procedure.
The output tuning is adjusted for filter shape. Once you are in the ballpark
then filter L and both C's are fine tuned.
Use your filter design program to determine the expected shape. With a
typical Q of 2 it will be very broad.
Once installed in the amp it will require final tweaking.
Carl
KM1H
>
> Thanks, Dan
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