Which Spectrum Analyzer Measures Very Low Frequencies? - Page 1
Forum section: electronics / beginners

author: TinyMirrors
author_rank: Contributor
timestamp: June 22, 2018, 09:26:36 pm
content: I've been looking at spectrum analyzers, but the problem I'm having is finding equipment that measures in the range of 0.1 to 100khz. The interesting areas for me are between 0.1 and maybe 1-4khz. What device might give me better information for lower frequencies like this. The more modern equipment seem like it's looking at very high frequencies, so I'm stuck trying to find a list of old equipment that could do the job.Thanks!

author: tautech
author_rank: Super Contributor
timestamp: June 22, 2018, 09:47:34 pm
content: Welcome to the forum.Others are in a similar pickle as most stop at ~10 KHz.There's a recent thread that might give you some guidance:https://www.eevblog.com/forum/testgear/looking-for-a-dynamic-signal-analyzer-with-extended-bandwidth/

author: innkeeper
author_rank: Unknown
timestamp: June 23, 2018, 02:15:25 am
content: What your looking for is more likely a DSA.Dynamic Signal AnalyzerI have an older unit, hp 3652ait is purpose-built for exactly that 64uHz -100khz range.happy hunting

author: w2aew
author_rank: Super Contributor
timestamp: June 23, 2018, 02:16:42 am
content: Quote from: TinyMirrors on June 22, 2018, 09:26:36 pmMost spectrum analyzers are AC coupled and start at 9kHz or higher. There are exceptions that go down to a few Hz. Most are pricey though. The Tek RSA5100 series effectively goes below 1Hz, but again, pricey for the hobbyist.Another option is a Dynamic Signal Analyzer. Still a bit pricey, but this a better fit for your application.You might be better off using a digital scope with an FFT function. With such a low frequency requirement, you can take advantages of it's hi-res (in-situ boxcar averaging) mode if it has it, to gain some resolution and dynamic range.

author: innkeeper
author_rank: Unknown
timestamp: June 23, 2018, 03:04:05 am
content: Tiny, could you tell us a bit more about what you are going to use it for? What kind of measurements you need, do you need tracking generation, will you be doing distortion analysis etc.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 23, 2018, 05:06:49 am
content: The SRS760/770 is another "audio spectrum analyzer" that can go from sub Hz to 100 kHz.If you can relax the 100 kHz requirement, a PC sound card may be the cheapest solution and can have quite high performance.If you need up to 100 kHz but don't want to spend for even a used audio spectrum analyzer / DSA, then you can look for a multi-function DAQ card like the ones from national instruments. You should be able to find one with a ~1 MS/s ADC, which will be good for up to a few hundred kHz no problem.

author: rstofer
author_rank: Super Contributor
timestamp: June 23, 2018, 05:37:47 pm
content: If by 0.1 you mean 0.1 kHz (seems reasonable from context) then the Analog Discovery II might be worth considering.Download the free software and play with the DEMO Spectrum gadget. If you want 0.1 kHz to be a major division, the maximum scale will be 1 kHz. If you can accept it being just 1 tick then 10 kHz. This isn't really a resolution problem, it is a scaling problem. If the Stop frequency is higher, ticks are worth more and more and there are only 100 ticks - by definition.https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/https://store.digilentinc.com/waveforms-previously-waveforms-2015/

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 23, 2018, 05:48:04 pm
content: HP 3577A, 3589A, 3588A, 3561, 3562, 35660A, 3585Anritsu MS4630 and others im not aware

author: TinyMirrors
author_rank: Contributor
timestamp: June 23, 2018, 09:18:21 pm
content: Hi innkeeper,We're moving an electro-static mirror. It's really small and delicate. Simply put, it works by applying a voltage across two terminals and the mirror moves accordingly. Since the mirror is so sensitive to voltage changes we are trying to find sources of noise in our electronics that may be causing the mirror to move or vibrate. We want to be able to set a voltage and stay at that exact angle for long periods of time. But if a specific frequency of noise is present the mirror can respond and may oscillate. We've tried using a cheaper scope to look at the fft for noise, but it's just not giving us useful information since each bin is 10hz and it's difficult to see what the frequencies are in the noise. We're looking for noise from the power supply or from other sources that may show up in the signal. We have found a sawtooth wave at a bad frequency for the mirror using the scope, but we're wondering what else we could find with better equipment. We have access to a keithley voltage and current source which can measure the voltage from our power supply as well, but the stability of the voltage is great according to that device.Thanks for the advice!

author: TinyMirrors
author_rank: Contributor
timestamp: June 23, 2018, 09:29:28 pm
content: I'm terrible at using forums, but thanks everyone for your replies!

author: innkeeper
author_rank: Unknown
timestamp: June 24, 2018, 01:44:18 am
content: that is certainly a job suited for a DSA.I saw MasterTech posted a nice list of DSA's but search DSA or Dynamic Signal Analyzer, and you will find many.spend some time reading the manuals for them.HP has a nice application guides and notes too for DSA's that can help you with your specific application, search for those as well.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 24, 2018, 03:07:22 am
content: Why not get an inexpensive ADC and then write some code? I use Python with the Numpy numerical library (all free) and its FFT is insanely fast. For the frequency range you want you can easily achieve real-time processing and the Matplotlib graphics library is very capable. With that combination of software and a tremendous online following, you can achieve great results with just a handful of code. You'll need an ADC with Python support. Mine is fromhttps://www.mccdaq.com/data-acquisition/low-cost-daq- they provide a great Python library. You can capture, FFT and plot in less than a dozen lines.FYI, a problem with solutions using a PC soundcard is that there's usually a low frequency cutoff at 10-20Hz which may be an issue.

author: 2N3055
author_rank: Super Contributor
timestamp: June 24, 2018, 08:46:39 am
content: PicoScope 4262.You can do FFT up to 1 Mpoints in provided software, and also have API to write your stuff (Visual studio, Python, Matlab).Top notch instrument for what you need.Regards,Sinisa

author: Lee Leduc
author_rank: Regular Contributor
timestamp: June 24, 2018, 03:22:00 pm
content: Take a look at the Digilent Analog Discovery 2.https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/Has a spectrum analyzer that may fit your needs.https://reference.digilentinc.com/learn/instrumentation/tutorials/ad2-spectrum-analyzer/startI use it in the lab for teaching Analog Op Amps. Very nice little tool for the price.

author: innkeeper
author_rank: Unknown
timestamp: June 24, 2018, 06:25:39 pm
content: It really depends if he is looking to do more experimentation with stuff, and roll his own, or play with various gear that might work or be writing his own custom code and debugging that OR if he is looking for a new tool that will give him the data he needs to do the task at hand. This dosnt seem like an application where someone wants to deal in maybe'sIt seems to me he is looking for the latter. Cost wise, yea some of the options could be cheaper in capital outlay, but once you factor in your time, probably not so cheap.In my own personal experience, I was able to acquire a nice OLD 2 channel DSA with a GPIB port, and an NI GPIB to USB adapter pretty cheap, and frankly has paid for itself 10 times over in time savings. It has its place.The other thing is that if you investigate other documented issues and testing of such issues, they will most likely be talking about DSA functions, analysis and results. Past research for such things was most likely done with DSA'sa DSA with 2+ channels is really the way I would go for all the above reasons, and if you need to go cheap, get one off ebay that's backed by someone reputable.again, not that you cant get away with doing it other ways, but, you will always be fighting the equipment to get it to do what a DSA does out of the box..

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 24, 2018, 06:59:12 pm
content: I don't know what the budget is but if you can find an HP3582A, it will do nicely. I used one extensively many moons ago. It's 2-channel digital 0.02Hz-25.6kHz.

author: tecman
author_rank: Frequent Contributor
timestamp: July 03, 2018, 03:26:23 pm
content: My Advantest R9211C covers 0.01 Hz to 100 KHzpaul

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 03, 2018, 06:43:15 pm
content: The latest Siglent oscilloscopes seem to have a pretty impressive FFT capability, and the scope's go down to DC. FFT is much better than you would expect from an 8 bit ADC.The FFT of my Rigol DS1052E is no more than a toy.Alternatively you might look into seismic equipment, or PC software such as Octave or Matlab.

author: innkeeper
author_rank: Unknown
timestamp: July 03, 2018, 09:50:11 pm
content: I have both an hp3562 DSA and a silent sds1104x-e (hacked to 200mhz) and there is absolutely no comparison, the fft function on the sds1104x-e doesn't even come close to what the HP DSA can do.. i mean not even worthy of being in the shadow of the DSA its that far different.I suppose if you got nothing is its something, but, frankly from a usability standpoint and doing real readings and analysis... it is a toy compared to the DSA.

author: coppice
author_rank: Super Contributor
timestamp: July 03, 2018, 10:14:35 pm
content: Quote from: w2aew on June 23, 2018, 02:16:42 amWhat is special about 9kHz that makes it the lower bound for so many spectrum analyzers?

author: innkeeper
author_rank: Unknown
timestamp: July 03, 2018, 10:43:31 pm
content: the first thing I noticed in my hp dsa schematic is the whole front end up to the DAC is DC coupled.there is a lot of balanced circuitry in there, and although there are a lot of opamps there are some dual fets that are internally matched and will track from a temperature standpoint.a lot of care is taken for LF noise entering the system.its a purpose-built system for dc-100khzgrab a schematic for a hp3562 or a 3561 and look at the front end... its interesting.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: July 05, 2018, 01:26:11 am
content: The applicable EMC standards require 9 KHz as a lower measurement limit.regards, Gerhard

author: coppice
author_rank: Super Contributor
timestamp: July 05, 2018, 01:44:46 am
content: Quote from: Gerhard_dk4xp on July 05, 2018, 01:26:11 amSpectrum analyzers were starting at 9kHz before things like ITU K.76 and CISPR 16 were around.

author: JS
author_rank: Frequent Contributor
timestamp: July 05, 2018, 04:19:25 am
content: The scope option isn't the best but you probably need an scope or already have one and might cut it for your requirements. Analyzing data in the PC is a great tool. Big memory depth would be your biggest friend for fft to be usable. Capturing a sample from the scope to the PC and running a script is quite easy and doable, I use my Rigol ds1054z and capture directly from matlab or octave via usb or network. I wouldn't even think using a pen drive, I did that in the university where I needed to take the samples hone to play around but doesn't make sense at home.Now you are just limited by your programming skills (and the 8 bits, but that's quite a lot with 24M of memory, as long fft gets things well under 1LSB)I think capturing data directly from the computer with an scope is a very very very useful tool for data analysis, the scope is a great tool for a lot of things as stand-alone, but post processing opens a whole different universe, given math functions of the scope are mostly toys. I think THE thing missing from scopes is the lack of user script addons as math functions! Maybe some have but I haven't came across them and I even less know the features and limitations they would have.JS

author: joeqsmith
author_rank: Super Contributor
timestamp: July 05, 2018, 03:50:06 pm
content: My old HP3589A is spec'ed down to 10Hz. Shown with a 0.5Hz signal using the high resolution narrow band. It is VERY slow. Many years ago, I was using an old HP3582 that was designed for this kind of work. It had two channels and I think it even had GPIB.Personally, for the 0.1 to 4KHz you are asking about, I would buy a data acquisition board and use the student version of Labview on a PC. Then you could do what ever you want.

author: Ice-Tea
author_rank: Super Contributor
timestamp: July 05, 2018, 03:56:25 pm
content: Just got a Marconi 2383 to work. Supposed to be between 100Hz and 4.2GHz. With trackking gen

author: billfernandez
author_rank: Regular Contributor
timestamp: July 07, 2018, 11:47:10 am
content: If 1.6Hz to 90KHz is an acceptable range, look at the Quant Asylum QA401:https://quantasylum.com/collections/frontpage/products/qa401-audio-analyzer

author: precaud
author_rank: Frequent Contributor
timestamp: July 07, 2018, 01:19:20 pm
content: You don't really need a DSA for this task. DSA's have two discrete measurement channels phase-locked to the generator for transfer function analysis/FRA. With their added complexity, these units tend to be large, heavy, and loud (fans).Any of the single-channel FFT analyzers from the 80's on that have selectable DC-coupled input will do the trick.Ono Sokki made some reasonably-sized ones and were well-built. Size-wise the HP 3561A isn't too bad. There were some smaller units from Nicolet, Spectral Dynamics, AND aka A&D aka Zonic, and others, often marketed as "mini-FFT", "personal-FFT", and the like.

author: radiogeek381
author_rank: Regular Contributor
timestamp: July 09, 2018, 10:33:01 pm
content: Just saw this thread.If the problem is low-level signals that are below (> 40dB) some other wanted signal in-band, you probably want a real-live spectrum analyzer. DSO's and FFT digitizers might do the trick, but the former is going to have limited dynamic range and soundcard versions of the latter might be just the trick, or burdened with spurious responses and noise sources of their own.Several posters have suggested various choices (R&S, and such) My choice would be an HP 3580A, principally because there's one on the bench. It doesn't get you down to mHz, but the specs cover 5 Hz to 50kHz, resolution bandwidths down to 1Hz. Dynamic range is a carp shoot, but the advertised "sensitivity" (whatever that means) is 30nV.I wouldn't pay a lot for one (for some reason there are a bunch on eBay for wayyyy too much money) I got mine > 10 years ago at a swap meet for about $100 (US).

author: bson
author_rank: Unknown
timestamp: July 10, 2018, 01:21:19 am
content: For low frequencies like < 10Hz I use my 34465A DMM with DIGI+MEM options and capture to a USB stick. Then decimate and FFT the capture. (A basic boxcar filter works fine for decimation prior to the FFT to get meaningful bin sizes.) Because of the high resolution capture it doesn't need a particularly long data set.

author: innkeeper
author_rank: Unknown
timestamp: July 15, 2018, 02:37:09 am
content: Tiny, what did you end up doing?

author: TinyMirrors
author_rank: Contributor
timestamp: December 14, 2018, 03:52:37 am
content: Hey! Just a quick update. I ended up borrowing a LabOne Spectrum Analyzer made by Zurich Instruments from another company. I ended up finding out all sorts of neat things about my circuits that I didn't realize. For instance, the cutoff frequency for a basic rc filter changes when biasing at different voltages such as 5V vs 100V. I didn't realize the ceramic capacitors could change so much. I feel like I'm learning a lot more than I expected.Thanks for the great advice guys! I'm still watching ebay for an HP3562. Hopefully budge and available line up just right one day.

author: cdev
author_rank: Super Contributor
timestamp: December 14, 2018, 01:24:15 pm
content: Have you seen the free "Spectrum Lab" software?https://www.qsl.net/dl4yhf/spectra1.html#downloadThe reason I ask is because many audio cards would qualify as capture devices at low frequencies, especially if coupling capacitors were removed or increased in value.It also runs under Wine on a modern Linux OS (just verified)https://www.qsl.net/dl4yhf/spectra1.htmlAnother similar program is Baudline.

author: sgilson99
author_rank: Newbie
timestamp: May 25, 2025, 01:11:28 pm
content: I finally found this one for around $50, doesn't quite go as low as you want but it might help you.https://ebay.us/m/Ou4iV6

author: MariuszD
author_rank: Regular Contributor
timestamp: May 26, 2025, 06:28:49 am
content: Quote from: TinyMirrors on June 23, 2018, 09:18:21 pmFor low frequency you can use USB audio card and make FFT on PC. Good quality card has great SNR.I had been using cheap scope with input amplifier to capture weak signals. Waveforms from scope was copied to PC. FFT was made on PC. Long buffer gives narrow bins. But only stable frequency sources can be found this way.Some noise sources don't have stable frequency, sometimes waveform analysis is more useful than FFT.Measure noise sources waveforms (switching mode converters, motors) in your circuit and search for it in actuator signal.

author: BennoG
author_rank: Frequent Contributor
timestamp: May 26, 2025, 08:18:44 pm
content: Today I tested with a pico scope to see if it was possible, and yes down to less then 0.1 Hz even lower if you use long sample time.I sampled about 1 minute of data and got way below 0.1 Hz with 1M buckets (the max you can set in picoscope)Benno

author: radiolistener
author_rank: Super Contributor
timestamp: May 26, 2025, 09:33:47 pm
content: You can use good sound card input as such spectrum analyzer.With good sound card you can get pretty nice dynamic range up to 120-130 dB.And even cheap one can give you 80-90 dB.

author: TimFox
author_rank: Super Contributor
timestamp: May 26, 2025, 11:38:46 pm
content: Quote from: sgilson99 on May 25, 2025, 01:11:28 pmDoes anyone have experience with this unit, or a list of specifications?