Is the sweep speed of a vector network analyzer important? - Page 1
Forum section: electronics / testgear

author: yangyao
author_rank: Regular Contributor
timestamp: June 09, 2025, 09:55:22 am
content: Is the scanning speed of a vector network analyzer important? I have seen micro VNAs such as NanoVNA and TinyVNA, and their scanning speeds are extremely slow, while professional and expensive VNAs have very fast scanning speeds, reaching tens of fps. Is the scanning speed a parameter that is of concern?

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 10:34:44 am
content: Quote from: yangyao on June 09, 2025, 09:55:22 amIt appears that a better question would be "how much are you prepared to pay for a faster scanning speed?"Clearly the answer depends on specific use cases, and you are unlikely to find many high-end use cases on a forum.

author: tautech
author_rank: Super Contributor
timestamp: June 09, 2025, 10:41:40 am
content: Quote from: yangyao on June 09, 2025, 09:55:22 amWith more experience you will discover the sweep speed is related to the # of sample points and the span.Add averaging for a more precise result and the sweep speed is slower still.

author: KungFuJosh
author_rank: Super Contributor
timestamp: June 09, 2025, 02:47:09 pm
content: Quote from: yangyao on June 09, 2025, 09:55:22 amSome of those nanoVNAs are significantly faster than others. Some bench models aren't that fast either. Yes, it matters. How much it costs determineshow muchit matters.

author: nctnico
author_rank: Super Contributor
timestamp: June 09, 2025, 02:57:40 pm
content: Quote from: yangyao on June 09, 2025, 09:55:22 amThe scanning speed is typically depending on the number of points per decade and the bandwidth. Lower bandwidth typically translated to higher dynamic range.To me scanning speed is very important. Having to wait minutes for a single measurement is a no-go.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 03:11:23 pm
content: Quote from: nctnico on June 09, 2025, 02:57:40 pmYes, buthowimportant?The only way I've found of answering that common question is to decide what I would be prepared to give up in order to get X. For a hobbyist that principally means money, and in an industrial environment it additionally means time (a surrogate for molney).

author: nctnico
author_rank: Super Contributor
timestamp: June 09, 2025, 03:29:21 pm
content: Quote from: tggzzz on June 09, 2025, 03:11:23 pmNahh, you just have to be sensible. For most network analysis measurements having like 50dB of dynamic range is more than enough. So go from there.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 09, 2025, 04:50:57 pm
content: Is it so slow that the drift effects your measurement? Do you need to let it run for an hour just to get a 110dB dynamic range? Maybe it sweeps fast but you can't offload the data into the PC before the next sweep?When putting together that electron paramagnetic resonant spectrometer, the LiteVNAs frequency would drift a fair amount during the measurement. The magnetic field was the highest contributor and I ended up sort of chopping the signal to get it to work.I want 120dB dynamic range, 1k to 20G, leveled output, 4X receiver, 3-ports, 10G Ethernet to the PC, for under $200.

author: nctnico
author_rank: Super Contributor
timestamp: June 09, 2025, 05:30:39 pm
content: The frequency range is also an interesting question. For PDN (power distribution network) analysis, you'd like to start at 100Hz to a couple of hundred MHz. For tuning wifi/bluetooth antennas the 1GHz to 6GHz range is interesting. However, if you want to measure a bandstop filter for wifi/bluetooth, you are looking at needing at least 13GHz

author: Miek
author_rank: Regular Contributor
timestamp: June 10, 2025, 11:54:53 am
content: Quote from: yangyao on June 09, 2025, 09:55:22 amFor me, there are two main reasons why scanning speed is important:First, it allows you to tweak certain settings without the measurement becoming absurdly slow. The sweep speed of the pro VNAs may seem over the top in the default state but it means that they can still be reasonable once you need to increase the number of points, decrease the IF bandwidth, or enable a bunch of averaging, whereas a lot of hobby VNAs would slow to a crawl. If you're tuning something, it's not much fun having to wait minutes or more for a sweep each time you make a change.Second, if it's fast enough to be essentially real-time, now you can use the instrument in a completely different way - you can tweak your circuit as you watch the result live on screen. I find this incredibly useful for things like antenna or filter tuning, tracking down particular issues with TDR on a PCB, or just generally building intuition about how a circuit will respond to poking at different nodes.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 10, 2025, 12:48:18 pm
content: Quote from: Miek on June 10, 2025, 11:54:53 amA very good point. When making demonstrations using the low cost VNAs, at times I would give up IFBW and samples to get the refresh speeds fast enough to show users what was happening live. In many cases though, there was only so much you could do and I would resort to speeding up the video.One of the last changes that Dislord made to the firmware for me allowed me to sample the data using the PC at 5kHz. Having a fast screen refresh wasn't the goal. Rather it was an exorcise to see if it was possible to process audio.

author: G0HZU
author_rank: Super Contributor
timestamp: June 10, 2025, 07:29:06 pm
content: Quote from: yangyao on June 09, 2025, 09:55:22 amThere's lots of reasons why it's important to have control of the sweep speed. This includes being able to slow it down, sometimes by a lot.With some lab VNAs, a slow sweep allows a (VNA controlled) power meter to be used to automatically calibrate/level the source for more accurate measurements. It can also allow the power of the source to be simply checked with a power meter.Also some devices under test will require a slower sweep speed. For example a narrow crystal filter will require a very slow sweep speed and often this will be slower than the default sweep speed for a given IFBW setting for the VNA.Where a slow sweep speed can become a major problem is when something like a 3 or 4 port VNA is in use after a full 3 or 4 port calibration across (say) 1601 sweep points with a narrow IFBW selected. This is where the modern lab VNAs can excel as they will have much faster hardware to handle all the processing involved when there are so many s-parameters being processed in order to produce each screen update. The older VNAs can be extremely sluggish when presented with tasks like this especially if the VNA is also doing some fixture simulation corrections as well.Having said all this, my old original NanovnaH generally does OK in terms of sweep speed but it only has 101 data points and it is just a TR VNA.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 10, 2025, 08:35:10 pm
content: Quote from: G0HZU on June 10, 2025, 07:29:06 pmJust an FYI, I think they bumped it to 401 in later firmware. Don't quote me on that.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: June 11, 2025, 02:19:49 am
content: Quote from: tggzzz on June 09, 2025, 03:11:23 pmit works like this:- when you have some thing you wanna check and it is stable in behaviour then sweep time does not matter cause result will be the same- if something is causing object that you are testing to change a bit (or a lot in characteristic) but for short period it will be like with oscilloscopes with smaller and larger dead time - you will catch that if lucky or will not see it and think it is OK... (but usually testing for this is taking place when there are money for it - other than that there is that added comfort as Nctnico and Miek mentioned and ease of making changes on the fly - but also at some cost of how many samples you are taking)Those very fast analyzers are usually not taking some huuuge number of measurement points - especially if you were looking at some older things that have more friendly pricing nowadays... There is always some trade in this - also you can purchase one able to catch lot of points and use it to sweep some band divided by subbands to have more accurate representation but then it will take "ages" to completeBut this is not always necessary and usually some cheap solution is totally OK but you need to know how this works to evaluate which is good for you (as for amateur I rather think it is a good idea to get some reasonable one and eventually pay a visit to friend having such "beast" of analyzer in case than to invest a lot and big, heavy 20-30 kg box on your desk and consuming not small amount of power, too - good if it will be used from time to time but do you need one on daily basis with such sophisticated analyzis speed?

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 09:23:20 am
content: Quote from: tggzzz on June 09, 2025, 03:11:23 pmImportant enough that it's one of the top selling features of our newest VNA, the ZNB3000https://www.rohde-schwarz.com/us/products/test-and-measurement/analyzers/network-analyzers/znb3000-launch_258011.html(It's not really a portable analyzer per se, but I did take mine golfing last week ..)Edit: hey, 1000 posts!

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 09:25:54 am
content: Quote from: nctnico on June 09, 2025, 03:29:21 pmThe biggest application where high dynamic range is important is filter measurements - it's easy to find filters with > 50 dB of rejection, and even > 100 dB is not uncommon.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 09:30:55 am
content: Quote from: G0HZU on June 10, 2025, 07:29:06 pmTrue, but I've never had someone complain that they couldn't slow down the sweep speed enoughQuote from: G0HZU on June 10, 2025, 07:29:06 pmMost mid- to upper-range VNAs will have a dedicated power calibration functionality (using a power meter, as you mentioned). I did a video on this a little while ago:Quote from: G0HZU on June 10, 2025, 07:29:06 pmThese are both excellent examples - thank you!

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 09:33:18 am
content: One thing to note is that mid- to upper-range VNAs often also have a "segmented sweep" functionality that allows the overall sweep to be broken up into sub-ranges, each with different parameters. This can speed up the overall sweep by using fewer points / wider IF bandwidths in the "less important" parts of the sweep.I have a video on this coming out today (I think) - will post a link when it's live

author: tggzzz
author_rank: Super Contributor
timestamp: June 11, 2025, 09:45:41 am
content: Quote from: pdenisowski on June 11, 2025, 09:23:20 amI have no reason to doubt thatBut that doesn't quite answer the full question, of course.If you indicated the list price, perhaps we and the OP could makeourdetermination

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 10:24:17 am
content: Quote from: tggzzz on June 11, 2025, 09:45:41 amTouchéThe short answer I would give is that sweep speed is not terribly important for many hobbyist applications, but most of my (non-hobbyist) VNA customers would say that speed is one of their more important considerations, especially in a manufacturing or production application.The NanoVNA sweep speed has never been a problem for me when I'm wearing my hobbyist / ham radio hat. If someone made a NanoVNA with a 10X faster sweep speed but at 5X the price, I wouldn't feel the "extra" performance justified the extra cost (again, as a hobbyist who is simply sweeping antennas or measuring a LPF, etc.)A brighter NanoVNA screen that I could read in full sunlight? That's something I absolutely would pay for

author: Fungus
author_rank: Super Contributor
timestamp: June 11, 2025, 10:33:11 am
content: So as usual it depends on what you're doing.If it's what you do all day long then yes, it's extremely important.If it's something you do once a month or so? Not so much.

author: tggzzz
author_rank: Super Contributor
timestamp: June 11, 2025, 10:37:22 am
content: Quote from: pdenisowski on June 11, 2025, 10:24:17 amSimilarly, I'd pay more for a NanoVNA that retained calibration when powered off. Or for one that didn't drop the calibration when a trivial change was made to the setup. Maybe other VNAs are better, or maybe there's updated firmware for my VNA. That indicates how much it is (not) worth to meBTW congrats on achieving a ton of posts

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2025, 11:44:44 am
content: Quote from: pdenisowski on June 11, 2025, 09:23:20 amI don't understand what golf has to do with a VNA? I have never played golf myself. The few times I have watched it, it seems the very opposite of fast. What does the photo try to convey? Does R&S give out green jackets with each purchase? I don't work in sales or marketing, and just don't get it.Reading the spec sheet:Measurement speed from 800 MHz to 1 GHz, at 500 kHz IFBW 1.3ms for 201 pointsDynamic range at 4GHz, 10Hz IFBW typical 150dBIf the focus really is speed, why not provide more data points? Better, provide the equations on how to calculate it based on the settings. Does marketing feel engineers primary focus is golf and making such a calculation is far beyond their skills? Why not provide 300 kHz to 4 GHz, 10 Hz IFBW, 16001 points?Makers of the LiteVNA could state, 1MHz center, 4kHz IFBW, 30 points can off load data to the PC at 200us. And it can do this for under $200.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2025, 11:49:42 am
content: Quote from: tggzzz on June 11, 2025, 10:37:22 amEven my first NanoVNA from 2019 could store the coefficients. I never run them stand alone but doubt they would have remove this.I wouldn't be surprised if they now include interpolation with reduced performance. Again, I don't run them standalone and such things are trivial on the PC.

author: tggzzz
author_rank: Super Contributor
timestamp: June 11, 2025, 12:13:21 pm
content: Quote from: joeqsmith on June 11, 2025, 11:49:42 amOh, that surprised me too. I can "store" them, but the stored values disappear when I power off.I've guessed it is EPROM missing or not working, but as I say, I haven't bothered to investigate.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2025, 12:33:10 pm
content: "Drives like a putter"

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2025, 12:41:08 pm
content: Quote from: tggzzz on June 11, 2025, 12:13:21 pmI assume you have what you stated, a NanoVNA and not one of the several other low cost VNAs. The schematics for it are available (attached). Note, it is minimal without an external E^2. Are you sure you actually selected save? I don't remember that being a problem, but I wasn't aware that slot 0 was loaded at boot time until later.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 02:54:44 pm
content: Quote from: joeqsmith on June 11, 2025, 11:44:44 amIt's not an "official" product photoWe were doing a customer appreciation event at a local driving range last week and I decided to take some "fun" pictures during setup.How is this related to golf? When I was in engineering school I was told that learning to play golf would help my career, so I took a golf class. Started as the worst golfer in the class, and ended as the worst golfer in the class. It would have been better for me career-wise to have spent that time learning how to use a VNAhttps://www.linkedin.com/posts/pauldenisowski_couldnt-decide-which-one-would-be-better-activity-7336203335810621441-CTUp?utm_source=share&utm_medium=member_desktop&rcm=ACoAAAAepm4BTn6t3KU9HHcL8iFKiS-v5j1E5hk

author: pdenisowski
author_rank: Super Contributor
timestamp: June 11, 2025, 02:57:31 pm
content: Quote from: pdenisowski on June 11, 2025, 09:33:18 amVideo on segmented sweep now live on the R&S YouTube channel:

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2025, 03:34:08 pm
content: Quote from: pdenisowski on June 11, 2025, 02:54:44 pmNow that you have covered the golf, how about some of the more VNA related questions?Quote from: joeqsmith on June 11, 2025, 11:44:44 am

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2025, 03:59:09 pm
content: QuoteMy wife's work also required her to golf. In my own career, it has never came up. My wife was much higher up the food chain.One day I came across her clubs and started hitting some balls out into a field. She took me to a driving range where they gave me a bucket of balls. They had some old cars parked out in a field. Wife was bitching about my holding the club like a baseball bat. I gave her the old, nobody cares. I was easily lobbing the balls into the cars. My wife was both ashamed of my display or improper technique and impressed with my range and accuracy. So she takes me to one of those children's putt putt courses. While I didn't kill or injure anyone. Rather than having any finesse it was more like watching an old pin ball machine in action. My wife showed me who's who and mopped up the floor with me.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: June 11, 2025, 04:27:13 pm
content: Quote from: joeqsmith on June 11, 2025, 03:59:09 pmpoint is to make you relaxed - so whatever works for you

author: mawyatt
author_rank: Super Contributor
timestamp: June 11, 2025, 05:43:42 pm
content: Like the idea of Paul's Segmented Sweep, been thinking about something similar to implement in the crude LCR Meter plotting routines we've created. This came up when we were plotting some Quartz Crystal Impedance plots awhile back and wanted higher resolution near the Crystal Series and Parallel Resonances but not suffer the long measurement time with the smaller frequency steps in areas of less interest.Anyway, thinking about what's going on during a sweep it seems the frequency must be stable long enough for the acquisition related to the "Effective Measurement Bandwidth" which is dictated by the composite IF Effective Bandwidth. If some signal processing like Averaging or other Digital Processing is taking place, then the frequency must remain stable during that period when the raw data is being captured. With this and the total number of frequency points captured seems to place a limit on the measurement speed. Having the ability to specify multiple parameters is the segmented sweep mode as Paul mentioned would allow the user to optimize the overall measurement time for a specific DUT without degrading the important DUT parameters while still achieving signifiant measurement speed improvement.Best

author: gf
author_rank: Super Contributor
timestamp: June 12, 2025, 07:40:56 am
content: Quote from: mawyatt on June 11, 2025, 05:43:42 pmAs the IFBW decreases, the measurement time becomes an increasingly dominant factor. For example, a selective synchronous detector with a simple rectangular window (sinc frequency response with low-selectivity, but zeros at harmonics) and a -3dB bandwidth of 10 Hz (as asked by Joe) requires a measurement window of~89 ms, rounded up to the next integer multiple of the IF period. If higher selectivity and higher stop-band rejection are desired (e.g. to block foreign interference signals), an even longer measurement window of around 200–250 ms becomes necessary.Having multiple receivers is helpful, as it enables multiple channels (reference, reflection, transmission) to be measured simultaneously. In contrast, single-receiver VNAs (such as the NanoVNA V2 and its derivatives; I think the LiteVNA also falls into this category) require multiple measurements per frequency point, with additional dwell time after each receiver switch.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 12, 2025, 01:42:03 pm
content: Quote from: gf on June 12, 2025, 07:40:56 amI wanted the 4 x receiver architecture to improve the calibration.One of the later features Dislord added was to allow me to turn off measurement. When I made that 5kHz audio test, I turned off S11. If I am only measuring S11, I can turn off S21. Saves a bit of time.