Not specific to the SA function per se but the use of the memory slots in from allow you to personalise the CMU200 to store stuff and setups. This I find very useful when using the SA. You just need a simple adapter card to compact flash. Thanks for the videos. Cheers.
Hi, nice video! I think it uses an FFT. As it would be the faster/cheaper way of creating all RBWs available on the analyzer. A way to check this may be taking a look at the internal LOs used, seeing if it jumps in discrete amounts (this jump length would be around the FFT span used at each step).
Yes, I had similar thoughts about checking whether the LO changes continuously or in steps. It would be nice to measure these LO signals, but the RXTX module is all encapsulated (with a thousand screws ;-), and I don't think the LO signals come out at some point. But perhaps there are people who know more (or already have done this ;-)
I'm actually very curious for this. Looking at the block diagram (service manual, page 3.2 , can be found here 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!
@@rudiselectronicslab861 Hummm, very interesting! I think this path may be used for low frequencies or for calibration at the factory.. If the AD was used as a dowconverter sampler, it would need a YIG preselector, I think.. Looking at the diagram, some different ideas came to mind. May it be running a sweep algorithm on the DDC block? Almost virtualizing the functioning of an analog sweep analyzer?
I took a bit different route to find this out… First, I examined an SA that utilises FFT to achieve faster performance at low RBW settings: an R&S FPC1500. Results are here: github.com/RudisElectronicsLab/RTB_SDS_DSOX_review/blob/main/Sweep_time-FPC1500.png. You can nicely see how, at some point, the FFT gets way, way faster than the classic sweep (note the log scales). Then I added the CMU200 results, see github.com/RudisElectronicsLab/RTB_SDS_DSOX_review/blob/main/Sweep_time-FPC1500_vs_CMU200.png. They really look like the FPC on swept mode only. With the RBW value getting smaller, the ‘sweep’ times get longer and longer, and we seem to see no point where FFT comes in to make them faster. So, this seems to suggest that, contrary to expectations, the CMU200 does not use FFT…
almost all R&S SA use FFT after down conversion to implement narrowest RBW filters digitally (eg 1Hz-10Khz or so). The wider RBWs are only analog filters. That speeds up the sweep quite a bit when you go down to those narrow bandwidths compared to having them in analog circuit
Regarding the markers on CMU it is actually possible to change the step size, you do this by pushing the left/right arrows in the frequency setting. Then it will move the cursor, i found it yesterday after bein frustrated regarding this for a couple of years :)
Thank you for taking the time to produce this video, it is very interesting and helpful.
Not specific to the SA function per se but the use of the memory slots in from allow you to personalise the CMU200 to store stuff and setups. This I find very useful when using the SA. You just need a simple adapter card to compact flash.
Thanks for the videos.
Cheers.
Thanks for that suggestion, did not think of it. Do have such a memory card, however, used it for firmware updates.
Hi, nice video! I think it uses an FFT. As it would be the faster/cheaper way of creating all RBWs available on the analyzer. A way to check this may be taking a look at the internal LOs used, seeing if it jumps in discrete amounts (this jump length would be around the FFT span used at each step).
Yes, I had similar thoughts about checking whether the LO changes continuously or in steps. It would be nice to measure these LO signals, but the RXTX module is all encapsulated (with a thousand screws ;-), and I don't think the LO signals come out at some point. But perhaps there are people who know more (or already have done this ;-)
I'm actually very curious for this. Looking at the block diagram (service manual, page 3.2 , can be found here 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!
@@rudiselectronicslab861 Hummm, very interesting! I think this path may be used for low frequencies or for calibration at the factory..
If the AD was used as a dowconverter sampler, it would need a YIG preselector, I think..
Looking at the diagram, some different ideas came to mind. May it be running a sweep algorithm on the DDC block? Almost virtualizing the functioning of an analog sweep analyzer?
I took a bit different route to find this out… First, I examined an SA that utilises FFT to achieve faster performance at low RBW settings: an R&S FPC1500. Results are here: github.com/RudisElectronicsLab/RTB_SDS_DSOX_review/blob/main/Sweep_time-FPC1500.png. You can nicely see how, at some point, the FFT gets way, way faster than the classic sweep (note the log scales). Then I added the CMU200 results, see github.com/RudisElectronicsLab/RTB_SDS_DSOX_review/blob/main/Sweep_time-FPC1500_vs_CMU200.png. They really look like the FPC on swept mode only. With the RBW value getting smaller, the ‘sweep’ times get longer and longer, and we seem to see no point where FFT comes in to make them faster. So, this seems to suggest that, contrary to expectations, the CMU200 does not use FFT…
@@rudiselectronicslab861 Very interesting investigation! Thanks!! We should make a video colab someday =]
almost all R&S SA use FFT after down conversion to implement narrowest RBW filters digitally (eg 1Hz-10Khz or so). The wider RBWs are only analog filters. That speeds up the sweep quite a bit when you go down to those narrow bandwidths compared to having them in analog circuit
I tried to find a way to find this out… Please see my reply to @AllElectronicsChannel below...
das ist toll unit
Regarding the markers on CMU it is actually possible to change the step size, you do this by pushing the left/right arrows in the frequency setting. Then it will move the cursor, i found it yesterday after bein frustrated regarding this for a couple of years :)
There are so many more things to find out... ;-)
CMU is obviously not a VNA. It has no SWR bridge....you must have meant Vector Signal Analyzer. Totally different thing than VNA
You are right... I knew this but nevertheless wrote it wrongly. I added an errata to the video at the points I mentioned this.