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

[Rick Parrish]

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.

-rick