Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!hplabs!hpl-opus!jewett
From: jewett@hpl-opus.hpl.hp.com (Bob Jewett)
Newsgroups: sci.electronics
Subject: Re: A question about the Nyquist theorm
Message-ID: <65200009@hpl-opus.hpl.hp.com>
Date: 19 Feb 91 21:44:23 GMT
References: <91046.095459F0O@psuvm.psu.edu>
Organization: HP Labs, High Speed Electronics Dept., Palo Alto, CA
Lines: 14

> > Just to nit-pick, it should be "GREATER then twice the bandwidth of the 
> > signal", not twice the highest frequency.
> 
> Wow, that's great! So I only need to sample my 10 Hz bandwidth signal
> which is centered at 1 MHz at 20 Hz!

Yes, that's almost true.  You also have to worry about how quickly the
sidebands and unwanted signals roll off, and about folding the
components of the signal of interest on top of each other.  The same
considerations apply to standard IF mixers as well.  A practical sampled
system with margins might be:  center of IF = 1MHz+50Hz, sampling rate =
200Hz.  This could be done with crystal filters.

Bob