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Re: [Discuss-gnuradio] Loops in graphs? Do we need them?

From: Rick Parrish
Subject: Re: [Discuss-gnuradio] Loops in graphs? Do we need them?
Date: Mon, 07 Feb 2005 23:53:55 -0600
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Achilleas Anastasopoulos wrote:

For instance, a PLL is a non-linear feedback filter that tracks the phase of an input sinusoid (approximately). In a DSP implementation we can recover the phase of the complex IQ signal and operate on it using simple FIR or IIR filters.

A PLL can also refer to other forms of feedback. Some loops might be more properly called PID (proportional-integral-derivative). In the case of some code I use, the PLL is actually used for clock recovery by operating on a digital signal captured in a sample stream.

Which reminds me ... I need to throw together some code that does symbol and clock recovery for a fairly low bit rate signal - a 1200 baud FFSK signal for an MPT1327 data channel. I'd like to do it without resorting to such heavy fisted tactics as an FFT or FIR filter. Anyone have any suggestions? I have a half-a**'d solution now but I'd like something closer to 100%. I'm not crazy about multiply-accumulate correlator techniques either.


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