On 04/04/2013 21:56, radams2000@gmail.com wrote:
[]
>> A couple of days ago I found an 'old' oscilloscope in the lab
>> which
>> 
>> reported a 1 GHz bandwidth, but when we looked up the specs it
>> reported
>> 
>> a 20 MS/s sampling rate.
[]
> Check out this link, under "sampling modes". With a repetitive
> waveform you can increase the effective sampling rate, but it doesn't
> work if you need single-shot capture.
> 
> http://www.ni.com/white-paper/4333/en

thanks a lot, I was not aware of such kind of sampling modes. Now is
much more clear why our signals didn't look at all what we expected!

On Thursday, April 4, 2013 3:36:39 PM UTC-4, alb wrote:
> Hi everyone,
> 
> 
> 
> I must say that this question may sound pretty silly, but I honestly
> 
> failed to find an answer.
> 
> 
> 
> A couple of days ago I found an 'old' oscilloscope in the lab which
> 
> reported a 1 GHz bandwidth, but when we looked up the specs it reported
> 
> a 20 MS/s sampling rate.
> 
> 
> 
> Now, my background is probably not supporting me much here, but a 1 GHz
> 
> bandwidth signal cannot be represented with such a low sampling rate
> 
> (Nyquist-Shannon sampling theorem). What am I missing here? (I guess a lot)
> 
> 
> 
> I started to look around in the labs and in catalogs and found that most
> 
> of the time oscilloscopes' sampling rates are - at least - twice as the
> 
> input bandwidth, which make perfect sense. Even in the case of
> 
> oversampling I may understand the reasoning behind (easier to make
> 
> anti-alias analog filter), but when sampling rate is below Nyquist
> 
> limit, how can the signal be reproduced correctly?
> 
> 
> 
> I am aware of the bandpass sampling technique for non-baseband signals,
> 
> but can an oscilloscope be targeted to such a particular case?
> 
> 
> 
> I'm sure there's a lot of literature on the topic but I must have missed
> 
> it in my searches.
> 
> 
> 
> Thanks,
> 
> 
> 
> Al
> 
> 
> 
> -- 
> 
> A: Because it fouls the order in which people normally read text.
> 
> Q: Why is top-posting such a bad thing?
> 
> A: Top-posting.
> 
> Q: What is the most annoying thing on usenet and in e-mail?


Check out this link, under "sampling modes". With a repetitive waveform you can increase the effective sampling rate, but it doesn't work if you need single-shot capture.

http://www.ni.com/white-paper/4333/en

Bob

Hi everyone,

I must say that this question may sound pretty silly, but I honestly
failed to find an answer.

A couple of days ago I found an 'old' oscilloscope in the lab which
reported a 1 GHz bandwidth, but when we looked up the specs it reported
a 20 MS/s sampling rate.

Now, my background is probably not supporting me much here, but a 1 GHz
bandwidth signal cannot be represented with such a low sampling rate
(Nyquist-Shannon sampling theorem). What am I missing here? (I guess a lot)

I started to look around in the labs and in catalogs and found that most
of the time oscilloscopes' sampling rates are - at least - twice as the
input bandwidth, which make perfect sense. Even in the case of
oversampling I may understand the reasoning behind (easier to make
anti-alias analog filter), but when sampling rate is below Nyquist
limit, how can the signal be reproduced correctly?

I am aware of the bandpass sampling technique for non-baseband signals,
but can an oscilloscope be targeted to such a particular case?

I'm sure there's a lot of literature on the topic but I must have missed
it in my searches.

Thanks,

Al

-- 
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?