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Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Capturing FM waveform on
Posted: Fri Nov 17, 2006 12:56 pm
Joined: Fri Apr 07,
2006 6:10 pm
There was an oscilloscope article written by
Steven B. Warntjes about sustained sample rate
in digital oscilloscopes. I wanted to get a
verification from the experienced users on this
group. Let's say I have an oscilloscope with
25000 sample memory depth and a real time
sampling of 1 gigaSamples / sec with 200 MHz
If I had an FM carrier
at 100 MHz with a 1000 Hz (1 mS period) test
signal modulating it, does that mean that a
digital oscilloscope with the specs above will
not be able to capture the waveform properly?
I was thinking that if the capture window
(in seconds unit) is equal to the memory depth
(in samples unit) divided by the sample rate (in
samples / sec unit), then the maximum capture
window that I can use and still maintain the
rated sampling rate would be 25 uS
So that means that if
my carrier signal is deviating between 100MHz
+/- 1kHz, then my capture window would at least
have to be 1ms/div to capture the deviation
properly (?). With a capture window of 1ms/div,
my sample rate would decrease to 25
mega-samples/sec, which is not enough to sample
the 100MHz carrier frequency.
I know that I can just use a
spectrum analyzer, but I wanted to capture the
waveform and duplicate the time-domain plot of
frequency modulation (amplitude vs. time) that
I've seen in the books.