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Date: Tue, 12 Dec 2006 17:52:45 +0100
From: Johan Bodin <jbodin@tele2.se>
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Subject: Re: LF: RE: SAQ Receiver for Window$
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Talbot Andrew wrote:

 > Would be possible to include 100Hz bandwidth option as well?

Yes, but SAQrx uses a complex FIR filter for the main
selectivity so it will take some CPU power if you want:

1. narrow passband width AND...
2. small ripple in the passband AND...
3. steep skirts AND...
4. large stopband attenuation

i.e. a "brickwall" response.

A complex FIR with, for example:

   Passband width = 100 Hz
   Passband ripple <= 0.1 dB
   Stopband width = 150 Hz
   Stopband attenuation = 80 dB (either side of +/-75 Hz)

designed with Parks-McClellan requires 2 * 1526 = 3052 taps.
The main filter in SAQrx is run at Fs = 11025 Hz.
I think ~3000 taps would work OK on a fast machine although
I haven't checked it. The existing 1000Hz filter has 2*206 taps.

You will have to choose a passband shift frequency (CW pitch).
Maybe 700 Hz is OK?

73
Johan SM6LKM