🚀 go-pugleaf

In article <605.27c28109@zodiac.rutgers.edu> bittel@zodiac.rutgers.edu writes:
>I had a professor that loved to explain the sampling theory this way.
>It is not correct!!!  What does the bandwidth have to do with it???
>Say you have a signal with frequency components from 5000 to 5100 Hz.
>The bandwidth is 100 Hz.. Does that mean you can sample at 200 samp/sec and
>get the signal??? NO!!

YES!!  Your professor was right.  You have to sample for all time, of course,
but you can get the signal.

That's why you need anti-alias filters, so you get the band you want.  Without
a filter, all the 100Hz bands you can think of get aliased to the same place.
0-100 Hz, 5-5.1 KHz, 1-1.0000001 GHz.

How do you think digital sampling scopes work?  The HP54501A has a 100 MHz
bandwidth, but samples at only 10 Msamples/sec.  Yes, I know these instruments
do a lot more than simple sampling, but they do acquire signals faster than
their sampling rate.  And they do alias, if you're not careful then
what you see may not be what you got.

>Enough said.

Apparently not, but this thread goes into the kill file real soon now...


				- Frederick P. Herrmann
				  fritz@caf.mit.edu