If only the baseband frequency is sampled at 6kHz then
information is missing to recreate the original 100kHz
and the sampling information is insufficient to
recreate the original signal.


This is analogous to saying the number 1234 can be
represented by
(1234-234) / 1000 = 1

If I supply the number 1.0 you can regenerate the
number 1234 from it? Not true, without the rest of the
sampling information. The sample is incomplete.

Bandwidth sampling only cannot recreate the original
signal.

"Me" wrote in message
...
In article
,
"daestrom"
wrote:

"Spehro Pefhany"
wrote in message
...
On Fri, 23 Dec 2005 18:46:49 GMT, the renowned
"daestrom"
wrote:


wrote in message
...
Joel Kolstad
wrote:

(I can't tell you how many times I've seen
people stating something
like,
'The Nyquist theorem requires sampling at at
least twice the highest
frequency present in the signal," when of
course it says no such thing.)

What do you think it means?


Nyquist figured out that higher frequency
components of the input signal
will 'alias' and you will lose the ability to
tell them from lower
frequency
components. In order to avoid 'losing
information' and not being able to
tell whether a particular sample stream was from
a low or high frequency
component, Nyquist's theorem states you must
sample at least twice as fast
as the highest component present.
snip

More than twice the bandwidth.



So, if I have a signal with a 1000 hz carrier, with
a bandwidth of 50 hz,
you think I can sample it at just 150 hz and get
accurate reproduction?
That's just wrong.

It is the maximum frequency component in the signal
that is important. The
bandwidth is not related unless the lower edge of
the band is at 0 hz
(whereupon the upper side of the band is equal to
the max frequency).

daestrom



You are getting your terms confused here guys.
Nyquist requires that
you input both the Center Frequency, and Bandwidth
when determining
the Sampling Rate. If the sampling is done at
BaseBand then only the
Bandwidth is relevent. If the sampling is not done
at baseband, then
the Center Frequency, and Bandwidth are required to
determine samling
rate. Example, if the Bandwith of the signal is 3Kc
and the sampling is
done at BaseBand then sample rate needed would 6Kc.
If the sampling is
done at 100 Mhz with the same 3Kc bandwidth, then a
200.006 Mhz sampling
rate would be required.

It is much easyier to do DSP at baseBand, than at IF
Frequencies, and if
you do DSP at IF Frequencies, the lower the IF
Frequency, the easyier it
is to do, and the slower the DSP has to run.

Me