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First picture on EEVblog of the new R&S MXO4 series oscilloscope :)

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Domitronic:

--- Quote from: goaty on September 29, 2022, 08:35:42 am ---I got the RTB2004-COM4 promo, so why not wait for the MXO4-COM4 package....

--- End quote ---

Well, looking at my budget i would need to wait for a MXO2-COM4 package  :D

Messtechniker:
Just downloaded the 574 page manual.  :scared:
Will keep me out of trouble over the next few days. :popcorn:

jjoonathan:
I am still trying to figure out the FFT architecture. From this video:


https://youtu.be/acE3d4TpiW4?t=46


it looks like changing the FFT settings also changes the time domain acquisition settings. Reducing the RBW 500Hz -> 400Hz -> 300Hz also reduces the sample rate from 1000 -> 833 -> 417 MS/s, which is what I would expect if the FFT were dependent on acquisition data (lower RBW => longer FFT window => longer acquisition) but not what I would expect from an independent FFT pathway.


The ability to have an independent FFT acquisition path would be very helpful for applications that require low-bandwidth-high-res time domain and low-bandwidth-high-frequency RF, e.g. looking at a power rail, spi bus, or VCO control at the same time as a corresponding 900MHz RF burst. On my bench, this is a very common situation. If the FFT must be calculated off acquisition data, the high fundamental frequency of the RF burst demands a high sample rate even though "morally" it has a lower information requirement driven by RBW+span. If the FFT and time domain have separate acquisition paths, these requirements are not in conflict, because the FPGA can send an efficient low-bandwidth-high-res time-domain trace alongside a low-bandwidth-high-frequency spectrogram, rather than a big high-bandwidth block of full-rate samples suitable for calculating both of them.


I want to believe that the MXO resolves this conflict with independent measurement pathways, but the video makes it look like the MXO has independent FFT in the more limited sense as the older R&S scopes, where you can trade off RBW against the number of stacked/overlapped FFTs, but you cannot have low-bandwidth-high-res time domain at the same time as low-bandwidth-high-frequency spectra unless you fill your acquisition memory with high-bandwidth samples. Could you clarify which definition of "independent" is in play here? Thanks. (EDIT: I made & pulled this same post yesterday, not wanting to cause out-of-hours work, but I was too slow and got an answer by PM anyway. Apologies.)

Rich@RohdeScopesUSA:

--- Quote from: jjoonathan on September 29, 2022, 02:22:44 pm ---I am still trying to figure out the FFT architecture. From this video:


https://youtu.be/acE3d4TpiW4?t=46


it looks like changing the FFT settings also changes the time domain acquisition settings. Reducing the RBW 500Hz -> 400Hz -> 300Hz also reduces the sample rate from 1000 -> 833 -> 417 MS/s, which is what I would expect if the FFT were dependent on acquisition data (lower RBW => longer FFT window => longer acquisition) but not what I would expect from an independent FFT pathway.


The ability to have an independent FFT acquisition path would be very helpful for applications that require a low time-domain sample rate but a high RF sample rate, e.g. looking at a low frequency power rail, spi bus, or VCO control at the same time as a corresponding 900MHz RF burst. On my bench, this is a very common situation. If the FFT must be calculated off acquisition data, the high fundamental frequency of the RF burst demands a high sample rate even though "morally" it has a lower information requirement driven by RBW+span. If the FFT and time domain have separate acquisition paths, these requirements are not in conflict, because the FPGA can send an efficient lowpassed time-domain trace alongside an efficient spectrogram, rather than a big inefficient block of full-rate samples suitable for calculating both of them. To the user, memory efficiency is visible as the maximum acquisition time when RF+DC pathways are active. If they are dependent, max acquisition time is milliseconds, but if they are independent, it can be many seconds.


I want to believe that the MXO resolves this conflict with independent measurement pathways, but the video makes it look like the MXO has independent FFT in the more limited sense as the older R&S scopes, where you can trade off RBW against the number of stacked/overlapped FFTs, but you cannot have low-sample-rate time domain signals at the same time as high-sample-rate FFTs. Could you clarify which definition of "independent" is in play here? Thanks. (EDIT: I made & pulled this same post yesterday, not wanting to cause out-of-hours work, but I was too slow and got an answer by PM anyway. Apologies.)

--- End quote ---
Good question - and I appreciate you not wanting to cause out-of-hours work  :)  I PM'd our planner to get an answer - here's what they replied:

Historically, oscilloscope FFTs have had dependencies between frequency domain settings (CF, span, RBW) and time domain settings (RL, timebase).  If you changed the RL or timebase in the time domain this would cause a change to the FFT RBW and the converse was also true.  For the MXO 4 we removed these dependencies.  So you can set the timebase as you want and set CF/Span and RBW independently.  With that said, you are correct that adequate sample rate is still a requirement for bandwidth in either the time domain or frequency domain.  Nyquist still rules.  For MXO 4 the sample rate determines a common maximum bandwidth value for both time and frequency domain.

-Rich

jjoonathan:
Ok, so it sounds like the FFT settings are independent but constraints still propagate to acquisition settings (low RBW -> long acquisition, high frequency -> high sample rate). That's still a very useful capability -- I certainly appreciate it on my RTO -- but it still leaves the tradeoff where if I simultaneously want two low-bandwidth things (say, 1MHz of DC and a 1MHz sliver of RF) I still have to fill my acquisition memory with full-bandwidth samples (2.5GS/s rather than, say, 1*5MS/s + 1*5MS/s).

Even so, the new capabilities are beautiful and I look forward to the day when the platform refresh works up to MXO6 tier  :)

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