[hpsdr] sampling

[Jason A. Beens]

You would get no information in the case you mentioned, but strictly
speaking the Nyquist theorem is violated because the sampling frequency
is equal to 2x, instead of greater than 2x the bandwidth of interest.
Sampling at exactly 2x would cause an alias to DC.  In this case the DC
value would be zero because we are sampling on zero crossings.    

I think, but am not certain, that the 192 kHz rate is simply being used
to over sample the audio frequency range (20-20,000 Hz).  I don't think
the high sample rate is being used to reproduce audio up to 86 kHz,
because dogs can't even hear that.  :) 

The over sampling provides extra dynamic range.  If you wanted the
performance a 192 kHz sample rate gives you but you only wished to
sample at the CD sample rate of 44 kHz, then you would have to sample
the audio data with a higher resolution ADC.  There is a limitation on
the practical bit-width of ADC's, and one solution is to sample with
less resolution more often.  

Hopefully someone knows definitively why the 192 kHz rate was chosen,
and then speak up on the list.  You have me curious now... I will have
to goo do some research.

Jason Beens
KB0CDN

-----Original Message-----
From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf
Of FRANCIS CARCIA
Sent: Saturday, April 21, 2007 8:08 PM
To: hpsdr at hpsdr.org
Subject: [hpsdr] sampling

***** High Performance Software Defined Radio Discussion List *****

Say you sample 30 mhz at 60 mhz rate and you just happen to convert on
the zero cross at 0 and 180 degrees. What information will you get? I
would think you would need to sample at least 4 times to catch real
information. Heck we sample audio at 192 khz these days so why ? That is
at least 10 samples per highest audio frequency. Frank and other
grasshoppers???


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