Jan-Erik Soderholm wrote:
> Twice the highest freq that you want to be able to
> reproduce from the original signal. Bandwidth has nothing
> to do with it, IMHO.

Yes it does, but you have to know the target frequency range when
reconstructing the orignal signal from the samples.  Think about it this
way: Each frequency band with width of 1/2 the sampling frequency is aliased
accross the complete baseband 1/2 sampling frequency spread.  This is
usually bad because there is no way to know which original band a baseband
signal came from, and information is therefore lost.  However, if only one
such band was known to be present in the first place, then no information is
lost and it is possible to reconstruct the original signal.  In other words,
each baseband frequency maps to one and only one input frequency allowing
the input to be reconstructed.

It works like a sampling oscilloscope.  A 1Ghz signal may be sampled every
1.01 cycles to yield a look-alike signal at 10MHz.  This can't be
distinguished from a true 10MHz signal by looking at the samples, but if you
know that 10MHz and other frequencies that would cause the same alias are
not present except 1GHz, then you have an unambigous true picture of the
original signal.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist