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From: Luns.Tee@f646.n250.z1.fidonet.org (Luns Tee)
Newsgroups: sci.electronics
Subject: Re: Re: A question about Nyquist theorm
Message-ID: <362.27CF6007@egsgate.fidonet.org>
Date: 1 Mar 91 20:04:11 GMT
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 b> I had a professor that loved to explain the sampling theory this way.
 b> It is not correct!!!  What does the bandwidth have to do with it???
 b> Say you have a signal with frequency components from 5000 to 5100 Hz.
 b> The bandwidth is 100 Hz.. Does that mean you can sample at 200 
 b> samp/sec and
 b> get the signal??? NO!! 
 
   I haven't formally studied any of this stuff, but I'm tempted to agree 
that the sampling rate being freater than twice the bandwidth is enough
to capture all information. What you sample may not necessarily be in a 
form from which you can reconstruct the original signal easily, but all 
th information is there to do so. My original way of thinking was that if 
you were to feed your signal through a frequency converter down to DC, 
your original bandwidth becomes your highest frequency. Sample this. 
Reconstruct it, and frequency convert it back to where it came from and 
you have your 5000 to 5100hz signal. You'd need some pretty good 
antialiasing however.
 
   But then again, if you take 200 samples/sec of your 5000 to 5100hz 
signal, provided there's nothing outside of that frequency range, 
everything in that signal will be intentionally aliased into 0-200 hz, 
without any overlapping. All the information is there, just getting it 
out is a little difficult.