Can a VNA replace a tracking generator on a SA? [Sloved] - Page 1
Forum section: electronics / testgear

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 17, 2024, 03:57:05 am
content: Hello,From what I have read, the tracking gen on a spectrum analyzer allows the SA to perform measurement S21. Is that all? Like, given the choice of using a SA or VNA wouldn't you just go with the VNA? Am I missing something? Is there some feature that the SA+TG can do that a VNA cannot?Thanks!

author: shabaz
author_rank: Frequent Contributor
timestamp: July 17, 2024, 04:07:55 am
content: An SA can do things a VNA cannot (and vice-versa). An SA can operate without internally generated stimulus from a tracking generator; i.e., an SA will show what's present solely from its input channel. A VNA requires a locally generated stimulus signal for it to operate.I suspect you're confusing the term "VNA" with "Spectrum Analyzer with Integrated VNA". Some basic spectrum analyzers come with built-in VNA.

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2024, 04:09:54 am
content: Quote from: ballsystemlord on July 17, 2024, 03:57:05 amS21 actually. Typo ?QuoteWithout a RLB, yes.QuoteA few years back and not too long after getting my first SA to explore the black magic field of RF I was in a similar dilemma and all my wishes were answered with the release of the SVA1000X range. SA and VNA in one unit !I've had 2 of these,1.5 and 3.2 GHz and SVA1032X remains one of my all time fav instruments.

author: moerm
author_rank: Regular Contributor
timestamp: July 17, 2024, 11:36:42 am
content: Let me put it like this:There are SAs, often in the form of a base station analyzer or somesuch, who mayseemto also have VNA functionality, e.g. by showing a Smith diagram, but very few actually really do.And there are SAs with a TG who can also serve as a network analyzer - but ascalarnetwork analyzer, not avectornetwork analyzer. The major difference: the latter also do phase.If you are in a tight spot and a crude and/or cumbersome measurement is good enough then a VNA may serve as a (somewhat "crippled") SA too. But nowadays with most (halfway modern) scopes doing FFTs, so does a scope.Hth

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 17, 2024, 01:02:27 pm
content: Quote from: shabaz on July 17, 2024, 04:07:55 amI knew that. I was asking so that I could determine if it was best to buy a SA with a TG, or if the VNA I also intend to get would do the job just fine.The architectures of the 2 instruments are different. So I was asking because, for all I know, the SA could do stuff with a TG, that a VNA wouldn't otherwise be able to do.

author: shabaz
author_rank: Frequent Contributor
timestamp: July 17, 2024, 01:59:52 pm
content: Quote from: ballsystemlord on July 17, 2024, 01:02:27 pmI cannot read your mind to determine what you already know (and others clearly cannot either from the responses). We simply answered based as best as we could.You didn't mention (in the original post) if the decision was between either an SA+TG, or both SA+TGanda VNA.I now think you meant to say something something along the lines of:"If I intend to purchase both a spectrum analyzer instrument and a VNA instrument, should I, in addition, purchase a tracking generator feature? Why would anyone use the SA's TG feature if they also happen to own a VNA?"If that's what you meant, then there are circumstances where one might prefer to use the SA+TG instead of VNA. For one, unless you've got a very high-end VNA, the dynamic range of the SA is higher. Also with SA+TG you'll be able to see measurements that otherwise might be buried in noise. But they won't be vector measurements. Also, less (and simpler) measurement calibration to do. Plus, some additional features may only be available with the SA and not with the VNA, and there may be differences in sweep speed. Plus with SA+TG, you can apply an offset between the TG frequency and the measurement frequency, which is useful when testing receivers. An offset is not possible with a VNA.

author: Bud
author_rank: Super Contributor
timestamp: July 17, 2024, 02:05:22 pm
content: Quote from: tautech on July 17, 2024, 04:09:54 amMagnitude |S21| actually. Typo?

author: tszaboo
author_rank: Super Contributor
timestamp: July 17, 2024, 04:53:14 pm
content: You need a TG+SA or a VNA if you are only interested in magnitude of linear systems.You need a VNA if you want to know the phase as well.You need a Signal generator, and a SA if you are interested in active components that will produce harmonics for example. But a high end VNA, with frequency offset can do that as well.So buy the equipment that measures what you want to measure. If you are interested in the frequency content of signals, then buy a SA. If you are interested in S parameters of linear systems, buy a VNA. Even though you might be able to measure S11 with a SA+TG and an external directional coupler, It's not something you want to set up daily.

author: pdenisowski
author_rank: Super Contributor
timestamp: July 18, 2024, 12:02:28 am
content: I would have phrased the question the other way around: Can a spec an with a tracking generator replace a VNA?The short answer is : it dependsFor very basic reflection (S11) and transmission (S21) measurements, a spec an with a tracking generator and a VSWR bridge is often comparable to a VNA is terms of functionality and results.I just (like, two weeks ago) finished a series of videos on our ZPH handheld VNA and our FPC1500 spec an, which has a tracking gen and internal bridge. I was using them both to (a) make basic antenna (S11) measurements, (b) measure cable loss, (c) perform distance to fault tests, and (d) measure filters. Quite honestly, the results for these particular tests were very comparable. [Videos are on the R&S TMF Playlist - link at bottom of post]Now, there are many, many, many differences between spec ans and VNAs and what they can/cannot do (well or at all). But for very basic measurements, it's often possible to use either one.Edit: here's a picture of an older HAMEG VSWR bridge - some modern spec ans with tracking generators have an internal VSWR bridge (this includes all R&S spec ans with TGs)

author: pdenisowski
author_rank: Super Contributor
timestamp: July 18, 2024, 12:15:43 am
content: Quote from: ballsystemlord on July 17, 2024, 01:02:27 pmIn terms of VNA-type measurements (S11, S21), I can't think of a single example of where I would need or prefer a SpecAn+TG over a VNA.Now, if I regularly made non-VNA-type measurements (e.g. IP3, channel power, occupied bandwidth, etc.) with a spec an and occasionally needed VNA functionality (measuring cables, filters, etc.), then I would want SpecAn + TG.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 18, 2024, 06:15:37 pm
content: Quote from: shabaz on July 17, 2024, 01:59:52 pmThanks, I sometimes find it difficult to phrase exactly what I trying to say/ask in a way that everyone understands.