This filter is shown in the LF Experimenters Handbook on page 25, as part of
the outline design for a narrow bandwidth LF receiver. The frequency
response I measured is given on page 26
If you view the output on a scope and hit it with a signal generator, as you
tune over the passband, the response first appears as a bouncing trace which
grows to its maximum over a few seconds. A step change causes it to ring
for a few cycles - but bear in mind that all filters (except Gaussian
designs) will ring. This just happens to be so narrow that the ringing is
clearly visible on a scope - it is a rather surreal experience actually
seeing the transmient response of a crystal filter in real time !
See you spotted the deliberate mistake on the spec, 50kHz impedance
Quite correct, it should of course read 50 k ohm
Andy G4JNT
----- Original Message -----
From: Ashlock,William <[email protected]>
To: <[email protected]>
Sent: Friday, September 27, 2002 3:04 PM
Subject: LF: RE: Re: Re: RE: Narrow CW filter using 32kHz clock crstals?
Hello Andy, Hugh, and all filter lovers,
I'm concerned about the transient response since this is the REAL measure
of
a good filter. How does it respond to a step input? It could ring for
minutes!
Hugh, please post the results of the spectrum test when you complete it.
Thanks,
Bill A
>Hello Andy
>I think I've answered my own question here.
>I built the filter and it doesn't work with 50 ohm input/output
impedance,
>but it DOES work with 50k ohms. Narrow isn't it ! I can just about hit
the
right frequency with >a signal generator and see some sine wave on the
scope. I haven't had a chance to put it on the >spectrum analyser yet.
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