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The quite limited frequency response in the 100 V and 1000 V ranges is a bit disappointing. Especially the low cut of for 100 V is odd, as there is the same divider and just the amplifier in x 10 mode instead of x 1. This corresponds to the 1 V and 10 V ranges, that seem to be fine to much higher frequency.
For 1 MSPS sampling the Nyquist limit is at 500 kHz - so there should be large drop in this range. If looking at more than just the pure RMS or peak to peak values, there should be signs of aliasing. So how does the waveform look for something like a 550 kHz signal, when measured at 1 MSPS.
It looks like there is no anti aliasing filter, not even a fixed one (e.g. 400 kHz) for 1 MSPS sampling.
Yes the 100V and 1kV ranges have bandwidth limited by the huge 10Meg divider. Internal changes when going from 100V and 1kV can make those differ a bit as well. The divider wasn't AC balanced because most of the user base doesn't do high voltage at high frequency generally.
There is an internal signal path difference based on selection 10M or Auto.
Measured the cutoff frequency in DigiV mode....For the 100V range, the cutoff frequency is 7.5 kHz.For 1000V, the cutoff frequency is 17.5 kHz.
Generally, the AUTO setting changes the input path with different amplifiers which is why you will always see noise differences and bandwidth differences.
I can say this behavior is planed to change on next hardware revision.
Would you consider posting your findings on the Tek forum or engage an applications engineer (Im not one - sorry) ?You might find you can get quicker / better answers by doing so. Just a thought to try and help you out.