I thought the RMS measurement issue was fixed in last (pulled) FW. Also, transient response, I thought you made the comment about an MSO1074Z measurement we saw on youtube. I did not see a problem when trying to test mine.
The RMS thing is a different problem we ran across in a recent discussion where we tried to test the analog versus DSO noise difference. I think what is going on is that the processing to produce the display record alters the standard deviation of the signal, which is not surprising, but it was a confirmation to me that measurements are made on the display record which I did not want to believe before. If you use RMS to measure noise on this DSO, it returns the wrong value; it is not even close.
For the transient response, I said the test was ambiguous in the Youtube video because we do not know the state of the feedthrough termination which was not used on any other oscilloscope. Later I was doing some transient response measurements and it occurred to me that transient response anomalies are limited by the vertical bandwidth; you cannot create nonlinearities which would add high frequency content with transient response misadjustments. Ok, that makes sense. But the results from the video do not seem to show that. If the feedthrough attenuator was bad, it should not produce that weird slant in the signal edge. What that waveform *does* look like is nonlinear distortion caused by an amplifier driven into cutoff or saturation or distortion during overload recovery.
Now Dave identified the transistors in the first differential stage of the DS1000Z as MMBT3904s and Rigol had to use emitter networks to boost the high frequency gain. That makes sense in comparison to much older 100 MHz oscilloscope vertical amplifier designs which had the 2N3904 available but did not use them. They either used faster transistors or they graded the 2N3904s for low base transit time (how is this done?) which suggests to me that those transistors are just not fast enough. That weird cross coupled differential cascode looks suspicious to me but maybe the differential tail current is low. Why is the differential tail current even adjustable?
So why didn't this show up in your test? Maybe Rigol grades these oscilloscopes like 2N3904s were graded in vertical amplifiers; if this is the case, the behavior would not show up in stock 100 MHz units. Or maybe your test signal was not fast enough to produce the behavior.
So the transient response thing might not be a flaw, but it sure looks like one based on the performance and the design unless it only shows up in Rigol's hacked for higher bandwidth.
I do not care if other DSOs do it or not; if they do, then they are broken as well. Them being broken does not fix the Rigol and my criteria for working properly does not include everybody else's product is broken also.
That's like saying that a Ford Fiesta is broken if it can't do 200mph and the fact that none of its competitors can do 200mph either isn't an excuse.
I do not *expect* automobiles to do 200mph unless I specifically bought them for that application. 200mph automobiles are rare.
I also do not expect the Rigol or any analog oscilloscope or DSO to have the fast overload recovery of a digital storage sampling oscilloscope or any sampling oscilloscope so that fact that its overload recovery is horrible is irrelevant. Analog and digital sampling oscilloscopes are rare.
If I had to pick two things wrong with the Rigol right now,
Out of curiosity, how many things can you pick that are right with it?
I can simplify the answer to it is better than an even worse DSO. I do not see it as a general purpose DSO because of its limitations. I came to the same conclusion about Rigol's earlier DSOs.
I have got a question though. Does making measurements on the display record mean that the Rigol actually has a record length of (checks manual, 600x800 display) 12 horizontal divisions * 50 points/division (estimated) = 600? Is the long record length only available when acquisitions are stopped? Wouldn't that make it like the early Tektronix DPOs?