January 12th 06, 08:02 PM
posted to rec.radio.shortwave
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Measuring filter shape factor
How exactly does one see 60db down?
Brian Denley wrote:
Michael Thorpe wrote:
Amongst all these political propaganda posts, I wonder if there is a
little room for a technical question related to radio please?
If so, here goes:
How does one measure the IF filter shape factor in a shortwave radio?
I am technically minded and do have a signal generator, etc., but I am
not sure of the exact procedure. Do I get the audio level at the peak
frequency, then detune both sides off the peak for -3dB of the
demodulated audio, note down the width between these points, then
detune to obtain for -50dB of the demodulated audio, get the width at
these points, and then the ratio of the two widths is the filter shape
factor?
I would appreciate a link to the exact procedure if there is one
(don't seem to be able to find this in Google) or an expert advice
please.
I would also appreciate advice as to what actual values of filter
shape are considered poor, good, excellent, etc...
Thanks in advance,
Michael
Michael:
If you don't have a spectrum analyzer, you can use an oscope (setup for
x-y) while driving the filter (and x ) with a sweep function generator.
Remember that if you look at the IF output prior to the detector, you will
get a curve going positive and negative. If you look at the response after
the detector, it will look more like the IF filter shape that you expect.
--
Brian Denley
http://home.comcast.net/~b.denley/index.html
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