Low frequency network analyzer recommendations? - Page 1
Forum section: electronics / testgear

author: hirada
author_rank: Regular Contributor
timestamp: October 23, 2020, 07:47:51 am
content: What options does one have when looking for an affordable NF (~1 - 1MHz)* network analyzer to display the frequency response of a circuit? So far I am aware of the Analog Discovery 2, but is there anything else that might be worth looking at? Let's say sub 6 - 700 quid? Used or new?PC based would be acceptable, since I already do own a low end picoscope, that is just unfortunately lacking the software, but stand alone would be preferred.Thanks* 1MHz probably does not really qualify as NF any more, but since most analyzers on ebay start only about a third of that and go up into the GHz rage, it is still acceptable. And if I do not reach quite that mark that could be ok as well, if the rest fits the bill.

author: uski
author_rank: Frequent Contributor
timestamp: October 23, 2020, 07:55:52 am
content: Take a look at the NanoVNA v2 Plus 4 :https://www.tindie.com/products/hcxqsgroup/4-nanovna-v2-plus4/$129 for 10kHz to 4 GHzMost VNAs will not go down to 1 Hz. For 1 Hz it is more in the domain of audio analyzers.Do you really need to go that low ?I used a Rohde & Schwarz UPL which does DC to 110 kHz but it is an expensive, discontinued and very specialized piece of equipment.The successor is a UPV and this is >$10k on the used market, not exactly cheap

author: hirada
author_rank: Regular Contributor
timestamp: October 23, 2020, 08:06:55 am
content: Wow, that was fast, thanks very much. Yes, I do need to go that low, as audio (no high end though) is a part of what I want to do, so 10kHz as a starting point is way to high, but I would like to have some headroom for the higher frequencies and I do not need those ultra tight specifications that audio analysers usually offer - in trade off for range.But I do have the QA401 on my radar, probably rather than the Digilent, as latter duplicates to much of my picoscope functionality and I am not too fond of its hardware with the BNC daughterboard hanging out in the wild. But it does offer a wider frequency range and is cheaper. And maybe there are alternatives.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 23, 2020, 08:10:06 am
content: Quote from: hirada on October 23, 2020, 07:47:51 amwhat application do you need such low frequency network analyzer? i think you can make setup from FG and your existing scope. do you really need S11? or we talking only S21?Quote from: uski on October 23, 2020, 07:55:52 amthose GHz VNA are not trustable at very low freq, i'm guessing below 10MHz, if we talk about S11. some limitation on directional bridge, but i havent checked closely the wheatstone bridge they are using.

author: uski
author_rank: Frequent Contributor
timestamp: October 23, 2020, 08:44:30 am
content: You could get an audio analyzer for the very low frequencies, and a VNA from Siglent (for instance SVA1015+) that goes 9kHz+ to 1.5GHzThe QA401 stops at a few hundred kHz from what I see in its product brief.Alternatively, some oscilloscopes from Siglent and Rigol have an integrated signal generator and offer an automatic bode plot function, which could possibly cover your entire frequency range. But I never used these features myself and I am not sure if they are good or suit your needs. If they do however, you could get away with a very cheap solution. Worth taking a look at it.

author: hirada
author_rank: Regular Contributor
timestamp: October 23, 2020, 09:03:44 am
content: Hello Mechatrommer,thanks for your reply, I would like to answer your question, but I am afraid, I have no idea what the practical meaning of FG, S11 or S12 are - besides being some form of specialized measurement after a quick online search.Well, being still a beginner, basically all I am looking for, as far as I have understood so far, is a bode plot. Just feed a device a frequency or amplitude sweep and display the response over that range. Nothing too special or fancy, I believe.What would be great, though, is to being able to have phase information as well. How does the phase of two signals in relation to each other change over frequency.

author: ch_scr
author_rank: Frequent Contributor
timestamp: October 23, 2020, 09:12:56 am
content: If all you need is a Bode plot (that includes by definition amplitude and phase information) an oscilloscope that with frequency generator (FG) and the necessary software to display it is your best bet for the give frequency range.As the signal will go through the thing you are testing (from it's "port 1" to it's "port 2") when measuring, it might be called a S21 measurement.I believe Keysight, Rohde&Schwarz and Siglent make applicable scopes.

author: hirada
author_rank: Regular Contributor
timestamp: October 23, 2020, 09:25:50 am
content: @uski: Thanks, I do believe, the sigilent is way above my budget and I still have hopes, I can get along with a single device, as I do not have that high demands. As of yet?But it looks like an audio analyzer is the way to go. Either a QA401 or by building a frontend to a soundcard like the one from Pete Millett, as I already do own a pretty decent one.At least to start with. I would not have expected for Digilent to have a de facto monopoly for general, non audio specialized bode plots, that still go low down (and somewhat up).@ch_scrQuoteThat seems to be the sole problem. The software needs to play with the hardware. My el cheapo picoscope could do all this, it just lacks that one option in the software. For a reason, I suppose. Unless I am missing something and if there is a generic software, I am all for it.I sure would not mind some slightly higher specs, somewhere in the middle between the pico and a full fledged audio analyzer, but I seems so far I am the only one and it would make at least for a good start.

author: Someone
author_rank: Super Contributor
timestamp: October 23, 2020, 09:36:18 am
content: Quote from: hirada on October 23, 2020, 07:47:51 amYeah, nah:https://bitbucket.org/hexamer/fra4picoscope/wiki/Home

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 23, 2020, 09:40:09 am
content: Quote from: hirada on October 23, 2020, 09:03:44 amahh. this is "Test Equipment" section btw. i asked because i wonder if there is ee discipline i'm missing. FG = function generator. S11, S21 is specific term for "network analyzer" i'm guessing what you are after (esp you mentioned audio) isspectrumanalyzer, notnetworkanalyzer. audio analyzer is one kind of spectrum analyzer with special purpose for audio and unusually lower noise floor and jitter compared to normal joe spectrum analyzer. these are to see your device's output purity or any distortion. otoh S11 is return/reflection loss coefficient, i havent heard this is a concern in audio industry, if one doesnt know this, it means its not his business. S21 is the forward gain/loss, this is most interest in many areas, that is Bode plot is one of it. you want to see what effect of output compared to input (magnitude or phase or both).so if you are interested in output purity alone, what you are after is spectrum/audio/signal analyzer, but if you care about signal amplification or attenuation, ie output with respect to input (S21), you are looking for spectrum analyzer (SA) with tracking generator (TG), or DSO with FG (function generator) that can give you bode plot, or a VNA (network analyzer). VNA can give you bode plot magnitude and phase, somewhat low noise floor, but only work at higher frequency than you requested. SA+TG usually can show magnitude only, but low noise floor, normal SA wont cut your 1Hz requirement, even the mentioned audio analyzer by uski only can go 10Hz and expensive due to audiophool nasty requirement (low noise). DSO+FG can give you nice bode plot, but not very low noise floor (limited dynamic range). so, what was your specification is?

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 23, 2020, 10:01:37 am
content: Quote from: hirada on October 23, 2020, 09:25:50 ami built a PC bode plotter/impedance analyzer sometime ago (snapshot attached) but only works for my DSO (DS1052E) and FG DDS3x25, but if you dont have programming skill, you may look around (google) Picoscope seems to have some writing maybe applicable to you?https://www.picotech.com/library/picoapp/frequency-response-analyzer-with-bode-plotshttps://bitbucket.org/hexamer/fra4picoscope/wiki/Homeif you want cheap/audio spectrum analyzer, some forum members swore by PC softwares that utilize your sound card with better dynamic range than a scope. you can google as well "pc/computer/windows spectrum analyzer" ymmv.

author: hirada
author_rank: Regular Contributor
timestamp: October 23, 2020, 11:18:05 am
content: Edit: The tool is still under active developement, I have just read the wrong copyright message.@someone:You made my day! Have of course not dug deeper into it yet, but by its requirements at first glance it may eventually even be able to run on linux! Of course developement has halted, but one never knows wether it does not get picked up again one day. And by upgrading to a slightly higher spec'd picoscope, it also may grow along.@MechatrommerThanks again for your time and in depth explanations.I indeed have wondered, wether I should ask in Beginners or here. But since we are talking about my quest for new test equipment, I threw a coin and went here.But I am not looking for a spectrum analyzer, I already do have this one my picoscope. So S21, if I understand your explanation correctly, is exactly what I am looking for. S11 is way above my head, but I suspect it is, what draws those nice wormholes on the screen.To jump right to your last sentence, DSO+FG are perfectly fine, I do not need an ultra low noise floor, I am not in the high end business at all, but I do need a FG/DSO combination with a software, that supports creating this report. Or rather a standalone device, that has been my hope.While there seems not to be such a hardware device,someonehas found the software! And you as well. Needs a test and a deeper peek at the thread over at picoscope, as it seem out of developement, but at least a very promising start.And in case I still have a XP VM with a passed though USB Card, that'll do the trick as a fallback, if the software should become incompatible with a new SDK.QuoteAnd somebody even has made a frontend for this method:http://www.pmillett.com/ATEST.htmAnd as mentioned before, I do own a pretty decent soundcard, somehow I just feel uncomfortable in using it as a mesuring device. Gotta really hate psychology. And software like mataa for Gnu Octave or Matlab seem to be quite powerfull, but come in at a rather steep learning curve.However, there are some interesting discussions about this soundcard solution vs. the QA401, but generally, they are all way above my humble requirements. May change in future.So for now I'll give the Fra4Picoscope software a go and see from there, where I will eventually be heading.Thanks again all for your input! Big help

author: Kibabalu
author_rank: Regular Contributor
timestamp: October 23, 2020, 02:58:15 pm
content: Quote from: uski on October 23, 2020, 08:44:30 amJust the spectrum analysis mode starts at 9 kHz. In network analysis mode the lower limit is 5 MHz, because of the Tracking generator

author: precaud
author_rank: Frequent Contributor
timestamp: October 23, 2020, 03:10:32 pm
content: Hard to beat the ol' HP 3577A for price/performance. I also wins the kg/$ race tooLow-frequency network analysis is often referred to as "Frequency Response Analysis" aka FRA. Keep an eye out for used units from Omicron, AP Instruments, and others. These require a PC to control them, though.

author: Kibabalu
author_rank: Regular Contributor
timestamp: October 23, 2020, 06:03:17 pm
content: Some scopes also have this function. E. g. the Keysight DSO-X 1000 and 3000 series. For some reason not the 2000 series. Unfortunately i have one of those :-(

author: switchabl
author_rank: Frequent Contributor
timestamp: October 23, 2020, 07:11:46 pm
content: There is also the ADALM2000, which is similar to the Analog Discovery with somewhat lower specs and a lower price. The software (Scopy) doesn't look quite as nice as Waveforms but it should do what you want.Both seem to be backordered in most places right now and the Analog Discovery has apparently become quite expensive. Although I see that amazon.de appears to have a few Analog Discovery 2 in stock for ~215€, which would be a pretty good deal. It's a really versatile little tool, especially with the 14bit ADC. May not be as intersting for you, depending on what Picoscope you have.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 23, 2020, 09:56:15 pm
content: Of course, don't forget that the Digilent Waveforms software (for the Analog Discovery) is free to download - and it works great with a regular PC sound card, using audio type frequencies obviously!There is no better way to get started than 100% free, right?

author: meteo
author_rank: Contributor
timestamp: July 28, 2025, 08:56:14 am
content: Quote from: Mechatrommer on October 23, 2020, 09:40:09 amThank you for your system answer. It was very helpful.I need to measure the "working range" of the capacitor, choke, LC filter frequencies. That is, the high impedance range where they will filter interference well.We are talking about the common mode and differential mode interference filter from 0 Hz to 1-3 GHz.What equipment is better to use here? If I understand correctly, I need S22. Is S22 similar to Bode in this case?VNA works at least from 9 kHz. And probably at minimum frequencies the data may not be entirely correct.If we talk about an economical solution.1. NanoVNA 9 kHz (70 dB) - 1.5 GHz (40 dB) HW 3.1. We measure S22 (impedance or decibels / frequency);2. DSO + FG (0-25 MHz) - we measure Bode up to 25 MHz (decibels / frequency).And in practice, to understand where the oscilloscope is better, and where the VNA in the range of 9 kHz - 25 MHz.What are the strengths and weaknesses of such a solution, can it change anything? We are not talking about precise measurements. The task is to roughly determine the operating range of the filter. Dynamic range / inherent noise / number of measurement points... for for these measuring devices.

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 02:11:29 pm
content: Quote from: meteo on July 28, 2025, 08:56:14 amFor high impedances at lower frequencies the DSO/AWG Bode Function or the Analog Discovery are your better instruments.Best

author: meteo
author_rank: Contributor
timestamp: July 28, 2025, 04:15:35 pm
content: I have R&S RTB2004 with Bode and internal waveform generator 25 MHz max. >80 dB. Is this an analogue of S22 at low frequencies? I think this should be enough at low frequencies.But frequencies up to 2-3 GHz are also needed. Should NanoVNA, S22 be used for these tasks? Let's say 1 MHz - 1.5 GHz.