28-09-2017, 08:11 AM
(28-09-2017, 02:06 AM)Nick Wrote: Bandwidth is never 10MHz - that's the sample rate.
With basic Nyquist the bandwidth would be 5MHz but more realistically is likely to be around 2.5MHz.
Yet my Fluke PM3380A Combiscope has a 100MHz bandwidth, despite only being 100MS/s?
That's because of Equivalent-time sampling:
Quote:When a DSO uses equivalent-time sampling, it can acquire any signal up to the analog bandwidth of the scope regardless of the sample rate. In this mode, the scope gathers the necessary number of samples across several triggers. The input signal must be repetitive to generate the multiple triggers needed for equivalent-time sampling. In equivalent-time, a slower, lower-cost digitizer provides the same accuracy on repetitive waveforms as a higher cost DSO with a faster sampler. For example, the TDS 460 offers a 350 MHz bandwidth with only a 100 MS/s sampling rate on each of its four channels.
I can't comment on this unit specifically yet, but as it's quite possible it has equivalent-time sampling, I wouldn't jump to any conclusions until I've tested it. And even if the unit as supplied doesn't support equivalent-time sampling, it's possible that someone will add it to the software in the future.
Equivalent-time sampling obviously can't be used for single-shot mode - that's when the sample rate becomes a relevant. In other words, the sample rate is not a measure of bandwidth in the conventional Nyquist sense; rather it's a measure of signal fidelity when using real-time sampling mode.
