[TenTec] Pegasus DSP Project

[Mark Erbaugh]

Is there anyone out there who is a DSP guru who could help me learn DSP?

I'm working on a project where I take the same Recv IF that is fed to the
Pegasus ADC and feed that to a computer soundcard line input. From there, I
demodulate the IF signal using custom built DSP software running on a
Windows XP computer.  I have been able to successfully demodulate AM and SSB
signals using some code I adapted from something I found on the web from
JI3GAB.  However, I need to learn how to design FIR filters with and without
Hilbert phase shifting.  Most of the resources that I've found seem to
assume that I will be using a commercial filter design program and that
those features will be in that program. What I'd really like to do is
include the filter design code in the DSP program so that the user can
custom design a filter on-the-fly rather than having to choose from a preset
list.

I'm currently using the Intel signal processing library (SPL). That library
has a routine that does a nice job of designing FIR filters with a zero
phase shift, but there doesn't seem to be a way to make it design a filter
with the 90 degree phase shift I need.  It there a simple technique for
changing the phase shift of an FIR filter?

I found some code on the web that will design FIR filters using the
Parks-McClellan method, but the code seems unstable when I try to design
more than 350 taps or so. I'd really like to try something like 2000 taps
(that should give me some 1.05 filter skirts).

Mark