Products > Test Equipment
Rohde & Schwarz CMU200
_Wim_:
--- Quote from: RBBVNL9 on May 28, 2023, 02:01:35 pm ---(but if this is the way the user is supposed to work, it would have been better of R&S to prevent a crash if the user did something different).
--- End quote ---
Yes, the software could certainly be much more robustly implemented and be more intuitive in use! I also believed for a very long period the normalization was not working.
--- Quote from: RBBVNL9 on May 28, 2023, 02:01:35 pm ---
* Using ‘Level sweep’ (great for detecting linearity issues!), the program sometimes performs the measurement as expected; at other times, it does not execute the expected sweeps.
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When getting "min level error", this is sometimes caused by the user specifying a level outside of the limits of the selected output. But apart from that, I also have had many crashes I could not explain.
--- Quote from: RBBVNL9 on May 28, 2023, 02:01:35 pm ---
* “Power Measurement Error” appearing at random moments. Repeating the exact same measurement later usually results in no errors. (It might be the CMU itself, but this is hard to tell)
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My CMU does this to. Not sure what is causing this.
With good remote software the CMU could indeed be a even more useful, but the amount of effort is quite big. I once started writing my own software, but gave up after realizing how much work it would be to achieve the features I wanted.
Bicurico:
As the author of the "VMA Simple Spectrum Analyser Software" I would like to thank Rudi for his review.
The particular version of my software for the CMU200/CRTU has never been popular, only few people use it. I want to believe that the reasons for that are:
1) There are not that many owners of a CMU200 or CRTU
2) The ones owning such a device, don't have a Keysight USB GPIB interface (note: I have a clone from China, which cost under 100 Euro and works without any problem)
3) People don't know about my software
Anyway, the absence of many users has refrained me from correcting bugs and continuing the development beyond my personal needs.
Hopefully I can iron out some of the issues Rudi mentioned and implement Wim's tip about the Regional Settings - boy has this caused me trouble in the past and i did not know there was this simple fix. This should be presented by Visual Studio as a message box on each new project!
And yes, I do believe that any old spectrum analyser capable of outputting the swept samples in a fast way (GPIB or network) can get a new life by means of a PC software doing all the data processing. This is what I did with my software - it was not designed as a remote GUI for the device and it's particular functions but rather a new implementation of a spectrum analyser that only communicates with the hardware spectrum analyser to set fundamental parameters like START/STOP frequencies and then receives the samples.
Ideally such a software should be universal and use specific DLL's to deal with the hardware communication. I failed to build the software like this because I never expected to grow it to this state. It might be simple and a professional programmer might replicate this in a better way in little time, but it took me several years (about 7 years, if I am not mistaken) to get to the current state, where I have versions for the R&S CMU200/CRTU, HP/Agilent 859x Series, Siglent SSA/SVA, SMA/NWT/D6/LTDZ, TinySA/TinySA Ultra, Anrist SSA.
A final note about the R&S CMU200/CRTU: they are fine test equipment that offer a great spectrum analyser. However, they are still sold at a price that defies the purchase of a brand new Siglent SSA3021-P, which can be crossgraded to a SVA1032. Compared to that, the CMU200/CRTU offer a better resolution and higher sweep rates (IMHO), but they lack measurement functionality. The main concern, however, is that they suffer from several issues, which need to be named. First off, many might have a broken or out of spec RF frontend. As a consequence, the specific selftest will fail and measurements will be out of spec. This is the RF input board. But the RX/TX boards can be faulty, too. Finally the RX/TX boards come with 1x (CMU200) or 2x (CRTU) Digital Boards. These are small daughter boards. When they fail, you won't be able to repair them and they are really hard to find. Additional problems come from the PSU and the PC board. I own 5x such devices. 4 are fully working, albeit the selftest does not pass 100% on all of them. One is not fully working (bad RF input board), but usable as a SA. Then I have a case with just the main board, that has some bent pins from the previous owner. Was purchased to remove needed parts for the other 4. This is to say that I started with two broken ones to rebuild one and ended with all of these...
Kind regards,
Vitor
RBBVNL9:
_Wim_
--- Quote --- With good remote software the CMU could indeed be a even more useful, but the amount of effort is quite big. I once started writing my own software, but gave up after realizing how much work it would be to achieve the features I wanted.
--- End quote ---
I'm not a programmer myself, but I certainly believe writing such code, debugging, making sure it works in different environments, and maintain it over time is a significant effort. Especially for a single person doing that in his/her own time. Also for that reason, I applaud Vitor's VMA program, which is useful but also very stable.
Concerning FreRes: I'd like to believe (expect?) that a leading M&E equipment provider as R&S does have the knowledge, professionals and resources to write good software. (This program was squarely aimed at its core audience, and already in version 5.30...)
As for using the normalisation function: both my CMU and my cables are fairly flat, and to make sure the normalisation was doing what I would expect, I did a little joke: I took a bandpass filter, normalized on that, and then did a measurement with input and output simply connected. That way, I should get the _inverse_ of the bandpass filter.
So I got what I asked for ;-)
_Wim_:
--- Quote from: RBBVNL9 on May 29, 2023, 05:01:41 pm ---Also for that reason, I applaud Vitor's VMA program, which is useful but also very stable.
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Fully agree!
I do think one of the reasons it was not more adopted is the fact some payment was needed. We live an age where people (incorrectly) think software should be free, because they are used to that when installing apps on their phone. However, app developers typically have others ways of making revenue (typically selling your data to others), which is not viable for software like the VMA program.
This however has totally killed the market for selling software.
--- Quote from: RBBVNL9 on May 29, 2023, 05:01:41 pm ---Concerning FreRes: I'd like to believe (expect?) that a leading M&E equipment provider as R&S does have the knowledge, professionals and resources to write good software. (This program was squarely aimed at its core audience, and already in version 5.30...)
--- End quote ---
Fully agree here also. I guess because they offered it for free, they did not care as much as they do for their payed software. Maybe this was written & updated by thesis students? :-//
RBBVNL9:
I’m having a conversation with someone whether the CMU200 actually uses FFT for its Spectrum Analyzer functionality. If it uses FFT in a ‘hybrid’ mode you would expect that its LO would jump in discrete amounts, where the jump length would be around the FFT span used at each step. Now, the relevant boards in the CMU (RXTX in particular) are very well sealed and it may be hard to get a probe there that could test that.
However, looking at the block diagram (service manual, page 3.2 , can be found here https://gotroot.ca/cmu200/CMU_Service.pdf) I see that the RXTX board has three IF frequencies (IF1 = 843.085MHz /1816.115 MHz, IF2 = 486.515MHz and IF3 = 10.7MHz), but ALSO features a bypass switch via which the entire front-end frequency band (e.g., 10MHz to 2.7 GHz) is connected straight away to the A/D converter!
Any thoughts?
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