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Re: [linrad] RE: Detecting phase modulation with undersampling

This seems like a fully digital RF lock-in amplifier, of which I have not seen an off-the-self model.

Disclaimer: I'm a Software Developer and amateur EE.

How about this?

R = real reference signal sampled at 65MHz
S = real signal of interest sampled at 65MHz

Down-convert R and S separately to two low bandwidth/sample rate complex signals, possibly with a 
CIC[1] filter but there is probably a better method, since CIC is well suited for FPGAs and ASICs.

At this point you could divide S by R (since the sample rate will be relatively low on the order of 
5KS/s the c6701 may be able to handle it). The resulting complex signal could be filtered some more 
to reduce the noise. At which point you could send the data up to the PC for storage, display, and 
further analysis.

You may also want to replace the R signal after down-converting with a PLL reference, but that sort 
of analysis is beyond me.

ref 1: http://www.dspguru.com/info/tutor/cic.htm

Dr. David Kirkby wrote:

Krzysztof Kamieniecki