There is no scope (including ones from Rigol) that say it is 200 MHz scope and will drop sampling below Nyquist, not mention well below BW frequency....
Solution is to call it 70 MHz scope and say it has 100/200 MHz limited mode... And limit BW when it breaks basic sampling theorem..
And Nico's GW Instek was never released that way, it was after unofficial hack. GW Instek was honest there.
What is wrong with you? DHO900 is a bad design. Why don't you want Rigol to fix it? Why do you want that your fellow Rigol users to buy badly designed scope... You're not helping Rigol..
"bad" design is based on your definition. a good scope must not alias? i think you didnt catch my reply to Howardlong. you cant avoid aliasing. you can feed your pure 70MHz to it and set the time scale large enough so the sample rate will reduced badly, and you get aliasing from your 70MHz. trying to add auto attenuation, will probably complicate the front end or FPGA logic cells hence increase cost... and it would not avoid confusion anyway... for the rest of us, we would like Rigol to fully open the front end BW to 1.25GSa/s divide 2.5X = 500MHz (or maybe 250MHz for 2 channels probing at 625MSa/s) like the old high end Tek/HP DSO... and later limit it ourself internally or external circuit if we need to. real circuit is not just viewing pure sine wave, there are other things like verifying risetime, gate capacitance and signal integrity on digital signal, that will not cause aliasing. if Rigol fullfill your theoritical utopia desire, then we will call it bad/crippled design, they wont be able to satisfy everybody. because this is subjective, as people call it horses for courses.
It is BAD design. It is only scope that cannot satisfy (and by factor 3x less than needed) Nyquist including Hanteks, UNI-T, Owon and all other scopes that are even cheaper.
I will repeat:
If you enable all channels (which is why you bought 4 ch scope) it cannot satisfy Nyquist at ANY timebase..
If you enable MSO too, then sampling rate drops below 1/3rd of needed sample rate.. At any timebase.
I even provided images what happens with signal when you feed 1 and 16MHz squarewave with quite slow edges (2ns edges) that is slower than Atmel MCU in Arduino by factor of 2-3...
In that case scope is USELESS. Because it will show garbage on the screen. It will be much worse than DS1000Z or DHO800 or and number of scopes that are very cheap and considered toys by many..
It is not about aliasing is not possible to happen with other scopes.
Problem is that on DHO900 you
cannot make it do anything else but alias all the time, if you use 4ch or MSO or God forbid be completely useless if you use both.. There is no setting that will NOT alias if you enable more than 2 ch and/or MSO.
So if you cannot use 4 ch or MSO, just buy DHO800 if you want to buy cheap 12 bit Rigol. That one works much better and is cheaper..