What they are trying to state is the Nyquist criterion; where a frequency can be represented by at least 2 points on the wave. So, 40 mega samples can actually capture a frequency of 20MHz max; with a caveat - the frequencies must be in sync or you will see aliasing. And no matter what, you cannot *fill in the gaps* if you have only 2 samples in one cycle.BitScope manages to pull off measuring one shot events @ 20MHz with only 40M samples. See; http://www.bitscope.com/design/
So, I guess this is ultimately my question; how do they do it? How in the world can a complex waveform be captured at 20MHz with only 40M samples?
I would reckon that the bitscope could capture with reasonable faithfulness an aperiodic wave @40Ms/sec uptil about 40/8 = 5MHz. Obviously, it will be better to have more samples to fill the gaps; thats where the sub-sampling term comes in - this is suitable only for periodic waveforms. The nearest possibility without sub-sampling is B-spline interpolation for single shot data.
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