R&S CMU200 as generic T&M equipment - Page 1
Forum section: electronics / testgear

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 16, 2018, 08:42:58 pm
content: Disclaimer: I bug T&M stuff, restore it and sell it. If I can, for a profit. I have a CMU200 for sale and I have two pallets more inbound (yes, 2 pallets). While my stakes in this are obvious, I tried to make the below as unbiased as possible. If you feel this is not the case feel free to propose changes.Some time ago, a member here was looking for a SG and I proposed the CMU I had for sale. While it is a unit conceived for testing cell phone communication of a previous generation, they often come with the optional SG. Same for the SA and power meter. As such, I consider it a good option for a general purpose unit. SG+SA+Power meter in a single package? What's not to like.Obviously, and as can be expected, some folks agreed, some others didn't. So I set out to compile a short comparison. The premises: you need a SG+SA and you need to choose between budget chinese units or an ageing but premium R&S unit. Specs first:Signal GeneratorThe CMU looses out on range. The 300MHz deficit in the upper range is perhaps defendable, too bad the lower limit is quite poor. Both are fairly evenly matched but the Rigol is a lot better as far as harmonic and non-harmonic is concerned.Spectrum AnalyserRange wise, the same story. The CMU can accept a *lot* more input power, which may prevent you blowing up the unit if you do something stupid (or if you have a very strong transmitter to measure). The CMU will accept 200W peak power. If you try that on the Rigol, make sure to have a camera runningThen again, the Rigol runs circles around the R&S as far as noise floor is concerned.Power MeterWell, it doesn't seem to be an option on the Rigol and I could not find a good candidate for a standalone unit. So, that's a win by default. Feel free to suggest a good sparing partner!Then again, a tracking gen is not an option on the R&S so perhaps we should call this even tooEase of useWell, only have the R&S so I can't comment on the Rigols. The R&S is made for 19" racks and is pretty bulky, the Rigols are most certainly smaller but there's also something to be said for not having three seperate units on your desk. In addition, the screen on the R&S is pretty good, a little bigger than the Rigol SA and a lot bigger than the SG. Even with the best of interfaces, I guess a 3-in-1 instrument will never be as easy to use as 3 dedicated instruments. Unfortunately, I wouldn't call the R&S interface as having 'the best of interfaces'. After some getting used to, I'd say it's fair but not much more than that. Keep in mind that the SA and SG are not the prime features of these things so "having an awesome interface for them" was probably very, very low on the priority list. Off course, I have some Rigol instruments as well and I wouldn't say they tick all the boxes eitherThe R&S has 2 in/out ports, 1 out port and 1 in port that can be flexibly configured, so it has that on the Rigols.ConclusionWell, in as far as I should be making a conclusion given my stake in this, here's my 0.02$. For both the SA and SG, there's something to be said for both but with all other things equal I'd have to choose I'd pick the Rigols.Then again, other things are *not* equal. I compared prices (without VAT, shipping and other cost) and I will probably be offering these CMU's for 1k€ or so (depending on options, perhaps, but for a unit with SG and SA) while you'd be out of 5k€ for a pair of Rigols. Which makes a CMU an interesting option, especially if you're just entering the game. You get a good unit and if you encounter its limits then at least you willknowwhy you will be spending a few €k more. And the R&S will probably hold its value a lot better than Rigols. Then again, if you already know the CMU won't be good enough you'll have to splash your money on something else.Let me know what you think. And if you want one, shoot me a PM

author: thm_w
author_rank: Super Contributor
timestamp: January 17, 2018, 10:41:58 pm
content: Was reading about the CMU200 recently. Can the options be hacked? There is also some audio analysis, that might be useful (20Hz - 20kHz or so).The killer for me is the lack of low end range (100kHz and 10MHz for SA) and lack of tracking generator.Great comparison though.

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 18, 2018, 07:19:36 am
content: Depends I suppose. If the unit does not have the HW module for the desired function you're obviously out of luck. But..https://www.eevblog.com/forum/testgear/enabling-options-for-rs-test-equipment/?topicseen

author: usagi
author_rank: Frequent Contributor
timestamp: January 18, 2018, 09:40:12 am
content: you can use the r&s software to emulate a tracking generator if you want to do things like characterize filters or antennas. it's not fast but it works very well and is basically an added feature for free.

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 18, 2018, 10:48:38 am
content: I think you are refering to this:https://www.rohde-schwarz.com/us/applications/freres-program-for-frequency-response-measurements-application-note_56280-15551.html

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 18, 2018, 07:25:09 pm
content: Hmmm... Found this:http://www.mwrf.com/test-amp-measurement/optimize-settings-improved-analyzer-sensitivityNoise Floor = DANL + Atten + 10log(RBW) (3)So, if DANL for the CMU is -100dB with a 1kHz RBW and -127 for the Rigol with 10Hz RBW then they would be 20dB closer for the same RBW? Any specialists here?

author: _Wim_
author_rank: Super Contributor
timestamp: January 18, 2018, 07:43:38 pm
content: Quote from: thm_w on January 17, 2018, 10:41:58 pm"Software" options can indeed be "added", but the most useful options are hardware options (audio, IQ-inout, 2nde generator...).

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 15, 2018, 09:40:41 pm
content: - Because... stuff. And reasons- Also, if you want one, I just... *might*, you know, have one for you...- Also: apparently, people think displays are an awesome place for stickers. They are not. And those people need to be shot.

author: Bicurico
author_rank: Super Contributor
timestamp: February 15, 2018, 10:23:31 pm
content: Holly cow!I want one...On a serious note, the stickers are glued on the screen on purpose. It is a way of convincing the bean counters that the device has been made unusable, aka broken, for fiscal reasons. You might actually thank the gyy that came up withe sticker idea.Much better than using a hammer.Regards,Vitor

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 15, 2018, 10:30:31 pm
content: Quote from: Bicurico on February 15, 2018, 10:23:31 pmGood!QuoteOh, you were not seriousQuoteWell, not in this case. The stickers were not applied by the original owners but by the auctioneers to identify the lots.

author: Bicurico
author_rank: Super Contributor
timestamp: February 15, 2018, 10:31:33 pm
content: In that case, shoot them!

author: thm_w
author_rank: Super Contributor
timestamp: February 15, 2018, 10:38:03 pm
content: Quote from: Ice-Tea on February 15, 2018, 09:40:41 pmHave you looked at what sort of options they have?

author: kamran
author_rank: Newbie
timestamp: February 15, 2018, 10:46:50 pm
content: Wow!And I thought I had a problem

author: technogeeky
author_rank: Frequent Contributor
timestamp: February 15, 2018, 10:48:18 pm
content: Man, I would love to get one of those. Unfortunately, you're in Belgium and the shipping costs alone would be more than I could afford to spend.Do you already have a handle on which internal components are worth selling after you make as many working and tested units as you can?

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 16, 2018, 09:01:01 am
content: Quote from: technogeeky on February 15, 2018, 10:48:18 pmWell, in case anyone is wondering:Shipping to Germany, France, Netherlands, UK: 40€Rest of EU: 80€Albanië, Algerije, Andorra, Bosnië-Herzegovina,Canarische Eilanden, Ceuta, Egypte, Eiland Man, Faeröer, Georgië, Gibraltar, Guernsey, IJsland, Israël, Jersey,Jordanië, Liechtenstein, Macedonië, Marokko, Melilla, Moldavië, Montenegro, Noorwegen, Oekraïne, Rusland,Servië, Sint-Maarten, Syrië, Tunesië, Turkije, Vaticaanstad, Wit-Rusland, Zwitserland enUSA: 100€QuoteEh, all of them? In case I can no longer frankenstein a working unit out of the bad ones, I'll break the remaining units up in pieces, check the parts against a working units and toss 'm on eBay.

author: babysitter
author_rank: Frequent Contributor
timestamp: February 16, 2018, 09:41:21 am
content: Consider a cleaner based on orange oil (not just smelling like orange) for sticker removal.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 16, 2018, 09:48:11 am
content: ...Orange oil? Eh, well, I'll take anything to shave off some of the time needed to clean them up

author: _Wim_
author_rank: Super Contributor
timestamp: February 16, 2018, 04:17:47 pm
content: I really like this stuff to remove old labels:http://uk.farnell.com/kontakt-chemie/label-off-50-200ml/label-off-50-200ml/dp/2142397

author: dcarr
author_rank: Regular Contributor
timestamp: February 16, 2018, 05:05:57 pm
content: I don't have time to make a measurement at the moment, but the CMU200 DANL is *way* better than that. You're mis-interpreting the spec sheet.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 16, 2018, 05:16:03 pm
content: Quote from: _Wim_ on February 16, 2018, 04:17:47 pmI had something like that before. Problem is it sometimes desolves or at least fades plastic. No problem at all for metal, very nasty for plastic screen films

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 16, 2018, 05:18:26 pm
content: Quote from: dcarr on February 16, 2018, 05:05:57 pmI suspect you are right (I actually more or less referred to it above) but I fully admit I don't understand it well enough to be sure. So I play it safe so no one can say it's untruthful advertising

author: _Wim_
author_rank: Super Contributor
timestamp: February 16, 2018, 07:12:10 pm
content: Quote from: Ice-Tea on February 16, 2018, 05:16:03 pmThanks for the warning. So far I did not have to you clear plastics yet, but did not see any discoloration on opaque plastics

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 16, 2018, 08:34:38 pm
content: I've had plastics turn to goo and others fade (the Tektronixs blue, in case you care)... HG sticker remover.

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 19, 2018, 07:48:41 pm
content: Dusting of a CRTU-RU. Pretty much like a CMU200, except for the 50W input (which is rare on CMUs) and the power coupler. Anyone suggestions for a good test for the power coupler (preferably using the unit itself)...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: March 19, 2018, 08:51:56 pm
content: So a CMU has a swept SA? I thought it was like most of the GSM etc. anaylizers, and had a fixed, FFT based spectrum analyzer. Damn, if I had known I would have bid more on one a few months ago.

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 19, 2018, 09:20:14 pm
content: Hehehe... feel free to shoot me a PM of you are interested in any way

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 22, 2018, 06:52:44 pm
content: Quote from: Ice-Tea on March 19, 2018, 07:48:41 pmOK figured it out. Used a CMU as second RF source. No settings, nothing. Learned some more RF stuff today

author: usagi
author_rank: Frequent Contributor
timestamp: March 23, 2018, 08:03:16 pm
content: Quote from: TheUnnamedNewbie on March 19, 2018, 08:51:56 pmit can be had cheaply on ebay because it has SA functionality but isn't sold as one. it's amazing value for the $.

author: corn11
author_rank: Regular Contributor
timestamp: March 24, 2018, 12:21:10 pm
content: Quote from: TheUnnamedNewbie on March 19, 2018, 08:51:56 pmIt has a (VSA)/FFT basedtopology. I've attached a cutout of the block diagram from the CMU service manual.*corrected s. below

author: tmbinc
author_rank: Frequent Contributor
timestamp: March 25, 2018, 07:23:56 am
content: It is a swept SA, at least for the spectrum analyzer mode. The RBW is implemented digitally on the DSP (and on their DDC ASIC). If you look at the files of the OPSW, you can find the DSP programs associated with the various RBW settings.It does _not_ have an FFT SA mode. But it can do other DSP-based measurements like Power, Freuqency, Power-over-time etc.; and then for the communication analyzer functions the baseband processing happens on the dedicated link units.

author: Bicurico
author_rank: Super Contributor
timestamp: March 25, 2018, 11:34:28 am
content: Tracking Generator implementation:https://youtu.be/qoHIg93_G9ERegards,Vitor

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 25, 2018, 08:07:23 pm
content: As an FYI: the ones with the audio option are now gone, at least the ones from units with little or no issues. Perhaps some of my "problem children" will turn out to have it once they are nursed back to health but right now no more audio units

author: corn11
author_rank: Regular Contributor
timestamp: March 26, 2018, 08:58:51 pm
content: Quote from: tmbinc on March 25, 2018, 07:23:56 amOk thanks for the correction my assumption was mainly based on the architecture which is of course identical if you use just some digital filters for the RBW but I asumed they would have gone the other way

author: Ice-Tea
author_rank: Super Contributor
timestamp: April 18, 2018, 11:05:41 am
content: One CRTU-RU gone. One remaining.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 18, 2018, 07:50:35 am
content: Second CRTU-RU gone.