Why R&S name some models Signal and Spectrum Analyzer - Page 1
Forum section: electronics / testgear

author: 2X
author_rank: Frequent Contributor
timestamp: June 04, 2024, 09:49:09 pm
content: Hello,why R&S name some models Signal and Spectrum Analyzer and some others just Spectrum Analyzer. As I know a Signal Analyzer (cost more) show more things over a Spectrum Analyzer. I read the below post but I couldn't find any big difference except what "Dago" say on his post. Do you have any idea about this distinction in naming... maybe the spectrum analyzer have some other advantages over a signal analyzer where R&S want to point out?Differences between Signal Analyser & Spectrum Analyser?https://www.eevblog.com/forum/beginners/differences-between-signal-analyser-spectrum-analyser/The Rohde & Schwarz signal and spectrum analyzer portfoliohttps://www.rohde-schwarz.com/products/test-and-measurement/signal-and-spectrum-analyzers_63665.htmlI am thinking to buy the below for my bench:https://www.rohde-schwarz.com/products/test-and-measurement/benchtop-analyzers/rs-fpc-spectrum-analyzer_63493-542324.html

author: DaJMasta
author_rank: Super Contributor
timestamp: June 04, 2024, 09:57:06 pm
content: Signal analyzers are meant for analysis of the baseband extracted from the RF carrier, so they have additional hardware/software to have this functionality. Often spectrum analyzers will have a limited demodulation capability (like AM/FM/PSK as audio output) and some will have an IF output for external analysis, but a signal analyzers will be able to decode more signals with more bandwidth and will give you more measurements of the modulation used.Of course, there's a lot of variety on both sides, but generally, a signal analyzer is a spectrum analyzers with additional capability for analyzing the modulation used in the incoming signal.

author: tv84
author_rank: Super Contributor
timestamp: June 04, 2024, 10:00:45 pm
content: Quote from: 2X on June 04, 2024, 09:49:09 pmPrecisely in that page, R&S describes the characteristics of both.

author: G0HZU
author_rank: Super Contributor
timestamp: June 04, 2024, 10:59:53 pm
content: There's probably a bit more to the signal analyser definition than the VSA capability it offers.I think that to fully qualify as a spectrum analyser, the instrument should have the design integrity to always achieve a certain amount of spurious free dynamic range (SFDR) no matter how it is configured with its various options. This makes it fit for the purpose of 'spurious free spectrum analysis'. The SFDR includes spurious responses such as IF and image responses.I don't think a signal analyser has to meet this global SFDR requirement. A signal analyser can be arranged to significantly compromise its spurious free dynamic range (eg it can compromise its IF and image rejection) in order to achieve a wider analysis bandwidth.Once the SFDR is heavily compromised in favour of the analysis bandwidth, I don't think the instrument can qualify as a valid spectrum analyser because it can also be prone to displaying lots of misleading spurious responses from out of band signals. A signal analyser is usually at its very best analysing signals that fall within its analysis bandwidth. It probably won't be very good at rejecting signals that fall well outside its analysis bandwidth when it is set to its widest analysis bandwidth.The other category is RTSA or real time spectrum analyser. Tektronix produced a series of RTSAs about 15 years ago including the RSA3408A (36MHz real time BW) and RSA6114A (110MHz real time bandwidth). These instruments could achieve quite good SFDR and so, in my opinion, they can still be classified as a spectrum analyser.The Agilent/Keysight PXA, MXA and EXA signal analysers can't always achieve a decent SFDR when set to the widest analysis bandwidth. So one could argue they no longer meet the basic SFDR requirement for a spectrum analyser when set to the widest analysis bandwidth.Obviously, the manufacturer will not be keen to draw attention to this SFDR limitation of a wideband signal analyser when it is compared to a spectrum analyser. So you are unlikely to find this stuff described in the marketing literature. You would have to study the datasheet and work it out for yourself...

author: pdenisowski
author_rank: Super Contributor
timestamp: June 05, 2024, 01:33:16 am
content: To be honest, I refer to them all as "spectrum analyzers" (well, actually just "spec ans") and pretty much every person I work with on that team also just calls them "spectrum analyzers"The FAQ on our webpage is how I would make distinction if I had to, but we have several instruments (FPL, FSVR) that can analyze and demodulate vector signals (cellular, Wi-Fi, etc.) but still have "spectrum analyzer" on the label. And our flagship analyzer, the FSW, has "SignalandSpectrum Analyzer" on the frontSo if we use the definition in the FAQ, the FPC would be a spectrum analyzer because it doesn't analyze or demodulate vector signals. That's pretty much all there is to the name.Incidentally, I have an FPC in my office right now, so please also feel free to ask me any questions you might have. I've already made about a half dozen videos on the FPC (see the R&S YouTube channel) and am working on some new videos this week showing how to use the FPC1500 for network analysis (that model has an integrated tracking generator and VSWR bridge).

author: pdenisowski
author_rank: Super Contributor
timestamp: June 05, 2024, 01:55:40 am
content: Quote from: G0HZU on June 04, 2024, 10:59:53 pmThe SFDR within the analysis bandwidth is actually the third "key fact" in our FSW marketing brochure (see attached)https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/pdm/cl_brochures_and_datasheets/product_brochure/5215_6749_12/FSW_bro_en_5215-6749-12_v1600.pdfI made an entire video explaining dynamic range (and SFDR) in spectrum analyzers because we absolutely want people to understand this specification

author: G0HZU
author_rank: Super Contributor
timestamp: June 05, 2024, 07:30:12 am
content: Quote from: pdenisowski on June 05, 2024, 01:55:40 amThanks. If you now apply your SFDR definition in the video at 6:45 to your signal analysers, what SFDR do they achieve when set to their widest analysis bandwidth option when used on the upper bands of the analyser? That is the point I’m trying to make.This is when the analyser downconverts to a low first IF rather than upconverts to a high IF.When a wide analysis bandwidth is selected, many signal analysers have to turn off the narrow YIG preselection in this usage case and this destroys the SFDR. Usually, the manufacturer buries this SFDR limitation in the datasheet and they don’t make it obvious that the SFDR collapses without the YIG preselector. It’s up to the reader of the datasheet to understand the implication that the SFDR collapses when the widest analysis bandwidths are selected.The true SFDR of an analyser includes all spurious responses including image responses and IF responses.

author: G0HZU
author_rank: Super Contributor
timestamp: June 05, 2024, 07:56:40 am
content: Another way to look at it is that a typical ‘wide IF’ signal analyser often loses its integrity as a spectrum analyser when set to its full analysis bandwidth. Once the YIG filter is deselected, you may find the image rejection collapses to almost nothing and the IF rejection might only be 30dB.The bandwidth of the YIG filter is typically less than the analysis bandwidth so it has to be deselected.Manufacturers of signal analysers tend to make this information as obscure as possible, often only describing the SFDR when the YIG is selected. It’s up to the reader of the datasheet to understand that the SFDR collapses without the YIG preselection. The YIG filter is quite narrow and it also introduces group delay and so it often has to be deselected by the operator as it can mess up the performance when analysing modern wideband digital signals for things like EVM.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 05, 2024, 09:09:37 am
content: Quote from: G0HZU on June 05, 2024, 07:30:12 amAnd it is an excellent pointYou're absolutely right about the challenges involved with SFDR in the scenarios you describe.Quote from: G0HZU on June 05, 2024, 07:30:12 amAnd yes, EVM performance has become one of, if not the, key performance parameters on the high-end for spectrum analyzers. We put together an entire webinar series on EVM because it's such an important measurement these days (5G NR, newer "flavors" of 802.11, etc.)https://tinyurl.com/mr3htv58I'll ping our EVM expert today and ask him about how we spec SFDR at different BWs, frequencies, etc.Note to@2X: sorry for the digression - none of this applies to the FPC since it doesn't do vector analysis

author: 2X
author_rank: Frequent Contributor
timestamp: June 05, 2024, 08:10:07 pm
content: Many thanks to all fo you for your replies. Indeed in R&S channel there is plenty of good videos.