Spectrum Analyzer - Rigol DSA815 - Page 1
Forum section: electronics / testgear

author: olsenn
author_rank: Frequent Contributor
timestamp: January 26, 2012, 09:27:39 pm
content: Hello everybody,I was just wondering if anyone has any experience with the new Rigol DSA815 spectrum analyzer, and if not, if you can tell me by the specs (http://int.rigol.com/prodserv/DSA800/) whether or not it's any good. Keep in mind that it is only $1500 (tequipment) so it won't compare to the high end analyzers. I really wanted a 3.0GHz one as to measure 2.4GHz signals, but what the hell, the 1.5GHz will work for most of the stuff I would need it for.What is the optional tracking generator, EMI filter (I can guess at this one), quasi-peak detector, and VSWR measurement kit used for? Are these essential for the operation of a spectrum analyzer?Thanks

author: joelby
author_rank: Frequent Contributor
timestamp: January 26, 2012, 09:57:10 pm
content: A tracking generator generates a test signal at the same frequency as the spectrum analyser's input frequency - if you connect the generator directly to the spectrum analyser, you would theoretically get a straight line. They're useful for testing RF filters or amplifiers - you can see how their response varies with frequency.A VSWR bridge allows you to measure the signal being reflected out of the device under test's input, which makes it possible to calculate the degree of impedance mismatch.They're both pretty useful things, really!

author: ejeffrey
author_rank: Super Contributor
timestamp: January 26, 2012, 11:25:53 pm
content: EMI filter and quasi-peak detector are for doing EMC pre-compliance testing. Basically, they are a set of IF filter and detection options that match regulatory requirements on EMC, so that your measurements can be directly compared with the requirements. AFAIK, there is no need whatsoever for these features in a spectrum analyzer that won't be used for EMC pre-compliance testing.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 26, 2012, 11:30:47 pm
content: Oh, if it wasn't clear: The VSWR bridge is almost always used with the tracking generator. You would feed the TG to the input port, the output goes to your DUT, and the return port goes to your spectrum analyzer. It is possible to use it with a separate signal source, but generally you will use the tracking generator.

author: Fraser
author_rank: Super Contributor
timestamp: January 26, 2012, 11:49:32 pm
content: It looks a nice unit. Compact and well laid out.I am using 3.5GHz Advantest R4131D's as I love their design and build. But they did cost GBP15K new ! I would be tempted by the Rigol for portable work but I have some 1GHz units for that so can't justify the purchaseNow the bit that may not be so good. My R4131D's use a YIG oscillator for the 1st LO and these can sweep a broad frequency range at excellent speeds to provide very fast scans of the spectrum even at 0-3500MHz spans.Some cheaper and more portable spectrum analysers have gone down the path of swept VCO's instead of a YIG oscillator. The result can be very slow sweep update speeds due to the PLL lock limits and VCO settling times. Such spectrum analysers can be fine for static carriers but spread spectrum and frequency hopping can be a challenge for them. MAX hold will eventually build up an 'image' of the hopper but it can take a much longer time than a YIG equipped unit. Anything that used DSO type techniques involving FFT should be carefully scrutinised. A poor implementation of FFT on a cheap spectrum analyser would be awful to use.With regard to frequency coverage. You can always build a simple downconverter for a particular area of the microwave spectrum. To obtain true RF level readings you would need a calibrated signal generator operating in the same frequency range and use the comparative level method of level measurement. That's how people used to use older spectrum monitors that had no calibrated amplitude.I personally would not buy this unit without first seeing it in the flesh or reading a review from a trusted source that details its true performance rather than just quoting manufacturers specs.If you are interested in viewing the 2.4 GHz ISM band, I can highly recommend the Ubiquiti Airview2. I have a couple of them plus a cheaper Chinese version. These units use dedicated ISM band receivers that provide 300kHz RBW which is sufficient for Wi-Fi, Bluetooth, Wreless cameras, RF ISM eavesdroppers & data links etc. My Airview2 units cost me only GBP30 ($45!) + p&p from the USA. IMHO no techie interested in ISM band stuff should be without one of these or similar units from Metageek .... Wi-Spy (much more expensive). They are relatively cheap, easy to use and designed for the task of monitoring ISM band activity with good sensitivity and level indication.Web links for you to look at:http://www.ubnt.com/support/airviewhttp://www.ebay.com/itm/Ubiquiti-Airview2-2-4GHz-USB-Spectrum-Analyzer-without-External-Antenna-Mac-PC-/370567158568?pt=LH_DefaultDomain_0&hash=item5647861b28http://www.ebay.com/itm/Ubiquiti-Airview2-EXT-Antenna-2-4GHz-Spectrum-Analyzer-/140601287787?pt=LH_DefaultDomain_0&hash=item20bc7d646bhttp://www.ebay.com/itm/UBIQUITI-AirView2-2-399-2-485GHz-Spectrum-Analyzer-USB-AirView-2-/170747611215?pt=LH_DefaultDomain_0&hash=item27c159c84fJust my 2 Cents worth.Aurora

author: RCMR
author_rank: Frequent Contributor
timestamp: January 27, 2012, 01:03:31 am
content: Review of the WiSpy unit here:http://www.rcmodelreviews.com/wispy24i.shtmlNot exactly a piece of lab-grade gear but a reasonable amount of bang for the buck.

author: sonicj
author_rank: Frequent Contributor
timestamp: January 27, 2012, 06:06:34 am
content: Quote from: Aurora on January 26, 2012, 11:49:32 pmdo you have any suggested reading on this topic? im borrowing a older hp analyzer that tops out at 1GHz and would like to look at 2.4.Quote from: Aurora on January 26, 2012, 11:49:32 pmdiscontinued mac supportwhats the cheap chinese version?-sj

author: Fraser
author_rank: Super Contributor
timestamp: January 27, 2012, 10:18:13 pm
content: Hi Sonicj,If you need to downconvert 2.4GHz to a sub 1GHz frequency, I recommend you consider adapting a ready built device rather than trying to build one as it is quicker and simpler especially if you don't have a 3GHz spectrum analyserI have modified MMDS downconverters for such a task. Take a look herehttp://www.qsl.net/g0ory/2.3g/lo2398/lo2398.html(this is similar to my units)http://www.qsl.net/n9zia/31732/index.htmlhttp://www.qsl.net/n9zia/wc0y/index.htmlhttp://www.amsat.org.ar/lu7dsu/mmdsconv.htmlhttp://www.ne.jp/asahi/m-arai/gkz/sband/convmode.htmhttp://www.scribd.com/anon-849269/d/40213396-Converter-for-Monitoring-2-4-GHz-Cordless-Phoneshttp://www.qsl.net/n9zia/wireless/2.4rxconv-pics.htmlhttp://www.qsl.net/n9zia/wireless/appendixF.htmlhttp://www.g3wdg.free-online.co.uk/modes.htmhttp://homepages.ihug.co.nz/~jpsl/downconverters_for_mode_s.htmhttp://www.markfossum.com/pdf/norsat.pdfCommercial units are well built, low noise and stable. Its a great way to improve a spectrum analysers frequency coverage but you do lose any calibrated amplitudes as the MMDS converter has masses of gainThe models I use were designed to fit a dish so had a dipole feed attached. Perfect for some 2.4GHz monitoringMine is UK sourced and was only GBP19 !!!! Great VFM. Try building a decent down converter for that sort of money....you'll be hard pressed to do so. The MMDS system was used in Ireland and the USA for certain so you should be able to find a supplier via ebay or a Google search.Have funAurora

author: NukerDoggie
author_rank: Contributor
timestamp: April 09, 2012, 05:10:26 pm
content: Someone here says the max scan rate for the Rigol DSA815 is 10ms. Not exactly sure what that means. Does it mean 10ms to scan the entire 9kz to 1.5ghz range?How would this SA stack up to the challenge mentioned here regarding seeing freq. hopping, etc? I'm seriously considering a purchase of this unit but don't want to get stuck with an instrument that is too limited or too slow.I REALLY hope someone here can do a review and teardown real soon!

author: nctnico
author_rank: Super Contributor
timestamp: April 09, 2012, 08:54:56 pm
content: Some professionals are very enthousiastic about this one:http://www.signalhound.com/The 4.4 GHz version is well withing your budget.

author: olsenn
author_rank: Frequent Contributor
timestamp: April 09, 2012, 09:06:29 pm
content: QuoteI'm not sure how much I would trust that one, but it does certainly look promising

author: echu
author_rank: Newbie
timestamp: April 09, 2012, 11:28:52 pm
content: I am close to ordering signalhound for work. There are several reports on this (mostly by ham radio operators) that are impressive. Consider this is a USB instrument that is achieving -150 dBm sensitivity, which means roughly it is able to resolve ~picovolt level signals. If I get one, I will report back.

author: nctnico
author_rank: Super Contributor
timestamp: April 10, 2012, 12:24:51 am
content: Quote from: olsenn on April 09, 2012, 09:06:29 pmI more or less regret spending my money on an old Advantest R3261Someone on an electronics newsgroup uses the Signalhound for some serious EMC work.

author: rf-loop
author_rank: Super Contributor
timestamp: April 10, 2012, 09:13:02 am
content: Quote from: echu on April 09, 2012, 11:28:52 pmQuote from: echu on April 09, 2012, 11:28:52 pm-150dBm in 50ohm system means that voltage rms is around 7.071nV (7071pV)dBm is power related to 1mW (this m is for mW)With 100Hz RBW it is (if -150dBm/Hz) around -130dBm (dependent also littlebit RBW filter shape specs)It need really understand what mean this noise level. (DANL)dBm/Hz !!! And even more, what really this average mean in practice working.(DPNL is raw and hard... they (manufacturers) do not want use it)(yes manufacturers do not always clearly tell this dBm/Hz... it is very fun example if minimum RBW is 1kHz or even more and manufacturer use dBmHz but talk dBm. Sometimes it is noted in one place with small letters and then they use without any worry just dBm. It is not clear lie becouse it really can find there if read all carefully. Some manufactures show it more clear some maybe forget whole thing.What it means?If it is -150dBm/Hz what if band width (RBW) is 100Hz. It is -130dBmWhat is displayed noise level in practice if RBW is 1kHz or 100kHz.It is good to know and realize so disappointment is then not so big.What span it is practical to use 100Hz RBW. How long time it take if set span example 100MHz and use 100Hz or 1kHz or example 10kHz RBW. (with 100kHzfilter it takes around one second! So it is really amazing slow! Old (very old) andslowR&S take same 40ms. With 100MHz span and RBW 100kHz and input attenuator 0dB. With this setting noise peak level is around -100dBm compared to this dogbox -65dBm. (oh well 35dB difference, not so big... more than 1000:1 in power )And this: "Frequency Sweepsup to140 MHz per second"There was one example picture in rewiew, 100MHz span, 100kHz RBW sweep time nearly 1 secondand noise peak floor seems be around -65dBm and maybe under -70dBm level can not detect anything. It is realistic. (with these used settings)Then this people who make rewiev and he look dislpayed average noise level... he use 100Hz RBW and then he adjust (normalize) numbers to dBm/Hz (dBm/1Hz) this is natural becouse also manufaturer use this, but it need remember what is dBm/Hz. Minimum RBW in this box is 100Hz.Residual spurious in input connector! Level is -- more bad than terrible. After reading this, if I see any serious lab work made with this box... I classify it as "garbage".But then, price! In this price: not bad for many kind of use where is not so critical for perfomance and accuracy.In manufacturer AD they tell it is high perfomance spectrum analyzer. ()If this is High Perfomance spectrum analyzer I'm caesar of China.It is low perfomance or entry level/hobby level spectrum analyzer but maybe not toy level.

author: Fraser
author_rank: Super Contributor
timestamp: April 10, 2012, 11:39:35 am
content: RF-Loop,Thanks for this insight into spectrum analyser specifications and how they may confuse buyers.With regard to teh OP's question.....Over the years I have learnt that, where spectrum analysers are concerned, you definitely get what you pay for. My Advantest R4131D cost around GBP15000 new and was considered an average performer by lab technicians. DDS, FFT and high speed ADC's are not the magic wand that makes a GBP15000 performance available for less than GBP2000. The Anritsu and R&S portable spectrum analysers had some pretty awful performance issues and they were 'state of the art' only a few years ago. The Anritsu ADC tram lined very easily indeed. These units still cost many thousands of pounds but were compromised by the need for compactness and use of new but embryonic DDS & FFT technologies.If your needs are hobby grade, there is no harm in buying a cheaper spectrum analyser, provided you accept the compromises that are necessary to attain the low production price. If you want performance on a budget, I recommend you buy a used brand name bench format spectrum analyser from manufacturers like R&S, Hewlett Packard, Advantest or Anritsu to name a few. They ARE better built and DO perform as specified.Remember, Spectrum Analysers have a sweep rate and the capture of a frequency agile signal like Wi-Fi isn't a simple task for such a unit. Each sweep will 'see' one or more signal peaks but MAX hold is the simple way to see the shape of the transmission and its related bandwidth and amplitude etc. As I have already stated, dedicated Wi-Fi tools are a good option and I just bought a n 'as-new' WiSpy 2.4x for GBP 80. The WiSpy is a well designed and very affordable solution to viewing Wi-Fi activity in an area.... more so than your average spectrum analyser...try lugging one of those onto a roof or antenna mast !Just my thoughts on the matterAurora

author: olsenn
author_rank: Frequent Contributor
timestamp: April 10, 2012, 12:59:24 pm
content: Anyone care to compare the specs of the SignalHound SA to the Rigol one (DSA815)? The scan rate on the former sounds to be very slow???

author: NukerDoggie
author_rank: Contributor
timestamp: April 10, 2012, 01:24:53 pm
content: Yes - Please! Compare the Dog Box and the Rigol DSA815.

author: olsenn
author_rank: Frequent Contributor
timestamp: April 10, 2012, 01:40:19 pm
content: QuoteYes, the 10ms refers to the scan rate throughout the entire displayed frequency range; so it scans from ~0Hz (displayed amplitude accuracy is just not guarenteed below 9KHz) to1.5GHz, 100 times per second. Of course you can manually decrease the scan rate (for example to 50ms).

author: NukerDoggie
author_rank: Contributor
timestamp: April 10, 2012, 02:11:11 pm
content: That would appear to me to be not that bad a scan rate. Certainly not up in the clouds with the $45,000 lab-quality units, but far above hobby and toy levels.

author: rf-loop
author_rank: Super Contributor
timestamp: April 10, 2012, 02:17:49 pm
content: Quote from: olsenn on April 10, 2012, 01:40:19 pmUsing what RBW? (if use speed where measurements are valid)Is it possible it can do it with 100kHz or 1MHz RBW?What is speed if span is 1.5GHz and RBW is 10kHz?In one picture it show:Span 5kHz RBW 100Hz sweep time 500msSo it IS not slow (but yes it is posible with today DSP).Old "state of art" R&S is 3 times slower in this case... (but beats Rigol of course in many accuracy related things and example noise floor etc etc)But 500ms for 5kHz with 100Hz RBW. Good in this class!(I do not know how this DSP technology etc affect but normal fundamental thumb rule is RBW/10 means scan time x 100.)------------------------other things ("dogbox spectrum analyzer")In 50 ohm system displayed average noise level (DANL).If manufacturer tell that displayed noise level DANL is (example) -150dBm/Hz(Note: sometimes they forget this /Hz)In theory (reference:http://literature.agilent.com/litweb/pdf/5965-7920E.pdf(Spectrum Analyzer Basics)):DANLRBW 1Hz -150dBmRBW 10Hz -140dBmRBW 100Hz -130dBmRBW 1kHz -120dBmRBW 10kHz -110dBmRBW 100kHz -100dBmRBW 1MHz -90dBmAlso this is just as old R&S workhorse show exept that it is of course better, and same for very very old work horse HP8568B what is even more better.Then I look:http://www.signalhound.com/Signal%20Hound%20RADCOM%20Review.pdfmanufacturer claim DANL 100MHz preamp off: -148dBm and preamp on: -161dBmThen I look review picture 1.Measurement start 100MHz stop 200MHz RBW 100kHz ATT 10dBWhat is wrong?Personally I do not believe this review (exept this picture 1) and I do not believe manufacturer specifications.There is 20-30dB somewhere missing. I understand some dB mistake and lie but if I tell I sell 100 ball to you do you accept you get 1 ball.So, what is trutht about this dogbox noise or do I understand something badly wrong?If set RBW to 100Hz and scan 100MHz, how long time it takes with dogbox?(very old R&S need 1980s) (with 100kHz RBW it use 40ms)In its price class it looks not bad at all, (on the paper). With 100Hz RBW and long averaging noise floor really looks like it is around -135dBm (50MHz) using preamp(!) if this manufacturer picture can trust. Also it is not slow. This machine in its price class can take seriously. It is not high end precision equipment but well better what I think before read more about it with my some experience.

author: NukerDoggie
author_rank: Contributor
timestamp: April 10, 2012, 06:25:47 pm
content: Today I've contacted Rigol-USA tech support and asked them to please provide more detail on the DSA815 Sweep Time specs.I asked them what the fastest sweep time and DANL would be for the 'worst-case' scenario of an RBW=100Hz and Sweep Frequency Span=9Khz to 1.5Ghz. I also asked them for same in other, less severe scenarios (those with a wider RBW and/or narrower sweep range).I told them it was impossible for me to make a buy decision without the additional information I requested, and that many other potential buyers would feel the same way. The instrument and its price look very attractive, but the low price raises more uncertainty, which needs to be dispelled (if possible) by more detailed information such as that I have requested.As soon as I hear back from them I will post the response here.

author: jahonen
author_rank: Super Contributor
timestamp: April 10, 2012, 08:43:35 pm
content: I wouldn't worry about such worst-case sweep speeds, in practice you won't use them. In fact, the sweep speed limitation comes mostly from RBW/video filter settling time which can't be circumvented, it is something like law of nature (narrower the spectrum, longer the settling time response and vice versa). Even if the sweep speed wouldn't be a problem, it is nicer that signals show up initially as reasonably wide peaks, then you can zoom into interesting ones. Also, phase noise and other FM instabilities of the local oscillator may prevent using very narrow RBW's.It is worthwhile to initially look at relatively wide spectrum and then verify that you are measuring what you think you are measuring. Strong out of screen signals can screw up your measurement or even damage the analyzer if you are not careful. This is because the first mixer sees every frequency component of your input signal, whether it is on screen or not.For comparison, R&S FSV7 sweeps 9 kHz to 1.5 GHz in about 5.7 seconds (as indicated on screen) in FFT mode (automagically selected) and 15000 seconds(!) on sweep mode with 100 Hz RBW. More practical example is a EMI measurement setup, which I use regularly, with logarithmic sweep from 30 MHz to 1 GHz with 120 kHz RBW, that sweep takes 674 ms (again as indicated). Or that 9 kHz to 1.5 GHz linear sweep with 100 kHz RBW, it takes 15 ms.Regards,Janne

author: NukerDoggie
author_rank: Contributor
timestamp: April 10, 2012, 10:18:58 pm
content: jahonen,You make some excellent points. Much appreciated!

author: NukerDoggie
author_rank: Contributor
timestamp: April 11, 2012, 08:57:58 pm
content: Well, here's the response from Rigol on the DSA815:See attached pdf from Rigol.Looks pretty decent to me - what do the rest of you think?

author: olsenn
author_rank: Frequent Contributor
timestamp: April 11, 2012, 09:53:36 pm
content: QuoteI'm quite surprised that Rigol not only got back to you, but also went to the trouble of putting together a document with screen captures and highlighted information. That being said, there are a few mistakes and other points worth mentioning. I own one of these units, and I have checked the results on my SA against the results reported in this document.First of all, all of the screenshots are obviosly correct, so there's no mistakes there; however, for the RBW of 100KHz (no screenshot provided) the sweep time is automatically adjusted to 150ms, not 50ms as stated in the document. Secondly, the 1500s listed for a RBW of 100Hz is kind of misleading; that is the correct value in terms of what the system recommends for that RBW over the full 1.5GHz range, but that is only because 1500s is the maximum sweep time supported by the device. As you will see below, it would take 150,000s to achieve the same fidelity at this setting.If you set the frequency to go from 0Hz to 150MHz, or 1GHz to 1.15GHz (or any 150MHz range) the values given are:RBW=100Hz, Time=1500s (Highest possible -- should be 15000s)RBW=1KHz, Time=150sRBW=10KHz, Time=1.5sRBW=100KHz, Time=15msRBW=1MHz, Time=10ms (Lowest possible -- only needs 5ms)As you can see everything gets scaled down proportionately; this makes sense since it will take 1/10th the time to sweep 1/10th the range while moving at the same rate. I'm not sure why it isn't linear based on RBW, but I guess that doesn't matter too much... you can easily tell just how much of a sweep time you need by increasing it and seeing if it changes the output at all (if it doesn't, then you're lower speed is good enough)Also, if you're wondering, setting the Auto SWT mode from Normal to Accy (High Accuracy) seems to tripple the sweep time. I don't notice any difference between the two outputs, so I'm assuming that's just Rigol's way of saying this way there's no chance in hell the time chosen isn't enough.