Spectrum Analyzer, Scope and FFT looking at Signals
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- Опубликовано: 28 сен 2024
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In this video I explain how a spectrum analyser (Tektronix MDO3000) can be used to view signals in the frequency domain vs an oscilloscope's time domain.
I give an overview of the logarithmic scale and its benefits vs a linear scale.
I explain how compound wave forms like square and triangle are made up of harmonics.
I do a practical demonstration of how the spectrum analyser works with some example signals. I then show how this can also be done on an oscilloscope using the FFT (fast Fourier transform) maths function.
* how to use a spectrum analyzer
#136: What is a dB, dBm, dBu, dBc, etc. on a Spectrum Analyzer? by Alan / w2aew
• #136: What is a dB, dB...
Video on the basics of RBW: • #119: Basics of Resolu... Here's my video on the basics of using the FFT function on a scope: • #65: Basics of using F...
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This guy really knows how to break down technical information into simple understandable words and scenarios. I really appreciate your videos sir. I have a much better understanding of how to use my oscilloscope now. Thank you.
Agree, a clear and easy to understand explanation and description of FFT.
The RBW setting will dominate the update rate on the spectrum analyzer. A benefit of reducing the Reference Level to be closer to the signal level is that the lower input attenuation will result in a lower noise floor - thus uncovering the lower level spurs and harmonics. The "spike" at the input is known as the DC Spur, or more accurately known as LO Feedthrough. It exists on all spectrum analyzers at the lowest end of the frequency range. You can add more "automatic" markers by lowering the threshold on the marker menu. You can have up to 11 automatic markers in addition to the two manual markers you showed. You can also have a look a the FFT function on the MDO3000 analog channel.
FFT resolution is similar to RBW - and is proportional to the waveform record duration in time. This is explained in my FFT video (linked below).
FYI - here's my video on the basics of RBW:
ruclips.net/video/Ffhs9Ny03lM/видео.html
Here's my video on the basics of using the FFT function on a scope:
ruclips.net/video/oRf-IpG6XAw/видео.html
***** Thanks Alan, I knew I would have some handy feedback from you. Thanks for posting your additional links, I'll add those to the other one in the video detail.I'll demo the FFT on the MDO3000 in the follow-up video with the other scopes.Cheers,Martin.
Wow, w2aew you're so awesome, love your videos.
I am hoping you keep up on your comments because I have something I'd like to ask you? I worked for Hughes Aircraft EDD (Electron Dynamics Division) back in the 80s and We used to use an oscilloscopes to tune the inputs and outputs of TWTs but I can't recall exactly how we did it. They where probably HP scopes and I think they had some B&C on the back. I am also sure that we used an SWR meter and we could also plot them out with different calibration lines, I think by varying the SWR meter?
Could something like that be done using these newer digital scopes?
Or is it something just those older analog scopes could do?
And is that something you might now how it could be done?
The reason I am asking is because I want to try something like that with coils.
I want to sweep different frequencies across them and I want to have a way of capturing that data for analysis.
I have come across something using a Wave on a string app that should work with a bifilar pancake coil. You may be ably to follow this, the center tap is dead center of the antinode when driving the coil at half a wave length of the wavelength of the length of wire used to make the coil.
I hope you see this, would love to know if you could help me.
Excellent video, Sir. Probably beyond the experience of most viewers. I did some harmonic measurement, analysis and mitigation on azimuth and elevation (DC) motors for WSMR illumination radar installations while working for Lockheed Martin back in the late '90's where we had high levels of even order harmonics causing a primary UPS to drop offline (half-wave rectification of the DC that drives the motors). The solution was a zero-sequence harmonic filter. I was able to duplicate the condition with PSpice. I loved that time of my career. I know I am grandstanding for a moment but I think you did an excellent job of addressing so many facets of modern instrument analysis. I am watching your video (and Alan's videos) because I am new to the FFT devices. All of my real-world work experience was with analog equipment. From my perspective, it is interesting that the computer driven (FFT) devices vs vintage analog devices, actually require a higher level of understanding to present a usable display. I am learning and I am enjoying. Really enjoyed your presentation.
Very good tutorial not only on how to use a spectrum analyzer, but why one would want to do so in the first place. Kudos, Martin! I especially liked the explanation of resolution bandwidth and how you put two signals side by side to illustrate it.
Nice Job. You explain things in a clear and concise manner that makes it easy to understand.
Thanks for doing this. Very well explained and has helped me understand a few things I had been struggling with for a long time! Good work, thanks again.
Old video, but thanks for pointing it out the advantage of FFT on a scope for some lower freq. vs. the RF work on a typical SA. Both have their place obviously. At this point there are real-time SA but still quite expensive. The most are still the sweep type with some DSP for the filtering. One more alternative these days would be SDR like RSP1A, with free SA open source software.
Excellent Martin. Love your easy-to-follow explanations.
Sir, you are really a wonderful teacher...thank you for this wonderful educational video.
A Spectrum is almost a must if you are going to be doing a lot of repairs on a full range of freqs. I had the Marconi back in the late 90's. when I owned a repair shop.
Love the way these topics are presented.
Thofus Thanks!
Excellent Explanation, Martin! Thank you very much for your time and efforts.
Thank you for such a detail informational video! I'm thinking of purchasing one..
Regarding 49:00 When using FFT on the scope, you want to view the waveform and make sure it's not clipping. As you adjust the scope settings or change the input signal, you risk the waveform being clipped off and this shows in the FFT as factitious spurs. I can't say that's definitely what's causing this effect in this example, but since you have 2 large 10Vpp signals and the first signal spur amplitude appears to decrease as you increase the second signal amplitude that's my guess. It's only a guess though, I'm pretty new to FFT myself as I have never had a spectrum analyser and only switched from analog to digital scopes recently.
What I have found on my Rigol DS1074Z is that as I adjust the timebase, I get lots of factitious spurs, almost like aliasing products. It looks like a comb filter. They change in frequency as the timebase is changed. There's only a narrow range of 2 or 3 timebases around 5-10 waveform cycles on screen in YT mode where I get a flat baseline on the FFT. I wonder if anyone can tell me where I'm going wrong there. I have recently updated the firmware and I haven't looked at an FFT since.
I also think the low frequency spur in the spectrum analyser is from the IF/LO. The 9kHz minimum bandwidth I think is to do with the downconversion but my limited knowledge of how spectrum analysers work predates it all being done in DSP. I could be completely wrong.
I see w2aew has commented on this subject, so I wouldn't even bother reading my last paragraph. I think I'm on the right lines, but he actually knows his stuff. :)
KX36 Thanks, I still appreciate your input. I'm trying to understand where the spurs come from and after a lot of reading (and still a lot more to do...) you realise the sources could be numerous. I will try cover that as well in the follow up video with the caveat that I may still be left with many questions myself...which I'm sure Alan will be able to assist with.
I wouldn't compare the reference power level on a SA to a volume control, as some actually have a volume and a speaker on them. It may confuse some that wish to obtain and operate one.
My HP SA has a volume control and speaker where I can find a local radio station, and actually listen to it. Likewise, it acts like a very wideband receiver where you can listen to every signal, especially an AM with a tone, from an RF generator.
Think of an SA as a large wideband sweeping scanner, with a video output, that logs signals based on their power as spurs.
Love your channel and your explanation
Loved the video so much. It cleared some doubts I had from college.
Thank you very much :)
Boby Robert Thanks for the post Boby.
As always nice job. I enjoy and learn from your videos. Thanks
this man knows what he is talking about.
Hello.
Many, Many thanks for your knowledge sharing and for so clear concepts exposition.
Just a question from my side: I am working in an EMC lab and the endless fight is always related to the RBW settings: the lower you set it you will gain in
-in signal resolution (of course :-) )
-in ground noise lowering/cleaning;
-but, of course you will need an higher time to measure the same span. So time=money, so the RBW must be kept high and the output curves moves from something absolutely nice and clean to a kind of confused noise disorder with some peaks that we suppose to be the real signal we were looking for. :-(
I also noticed that the more you reduce RBW settings, the more it could bring down also the interesting signals measurement themselfs. And, for a certification Lab, this is the worst nightmare.
If the RBW is not always set to the lower level as possible, there should be a reason.
Could you please explain where the thread-off limit is about RBW. In which relation is it with measurement points setup.
What are the parameters which tells you when to stop to decrease RBW?
Thanks a lot.
I'm looking forward to see the FFT performance of the Siglent SDS2072!
Nice videos! One question: Why does the Agilent sample at 2 GHz when it only has 70 MHz of analog bandwidth? Doesn't the Nyquist theorem tell us that the sample rate needs to be double the highest frequency you want to capture? I understand that the 70 MHz ain't no "hard limit", but the point where it starts attenuating the signal, however, this is more than 14 (!!) times the sampling rate than what would be needed if it were to capture up to 70 MHz. What's the reason behind that?
Nyquist theorem is minimum for voice sampling and reproduction, but for signal analysis is better to sample as much as possible regardless of analog BW
wow503 . Think of a strobe flashing at 10hz on a disc rotating at 10 times a second. A stripe on the disc will always appear at the same place. But it will also look the same at 20 rotations a second no way to tell the difference. If you double the strobe (sampling rate) and see two stripes 180 degree apart you can now descriminate. A square wave is composed of a bunch of harmonics to look at all square you have to sample fast enough to capture those higher frequencies. The 2gig sample rate might also be divided across multiple scope inputs. There's also the analog front end bandwidth on each scope channel to consider before the adc does its sampling. I think the fft slowing down as you ask for more resolution is driven by having to wait to capture more samples then crunch the numbers.
Hi. Would you know why is the time domain signal "wiggle-and-jiggle" on your Agilent oscilloscope? I have seen the same behavior on the cheapest units, probably due to lack of sample frequency and poor interpolation, but this one likes to have plenty with it's 2GS/s. Quite annoying I would say.
...oh I see, the signal is quite small, mV range 👍
Good topic, now how do I hook up my scope with FFT to an antenna ;) to see when stations come up on HF? I wonder if this is possible, maybe need a wide band preamplifier? Thinking, thinking ... oh it hurts ... thinking ;)
I would guess that the spike at the start of the spectrum is due to a tiny DC offset from the incoming signal.
Strange -in 13:05 it shows that the span starts at -70MHz what doen -frecuency means? Is it 180 degrees fase shift?
If you can find a better teacher on this subject, anywhere, I will give you a beer.
I assume I will keep the beer for myself.
Ingvar Nilsen, Norway (professional programmer, electronics hobbyist)
After viewing a handful of view on FFT basics, I found yours to be the most thorough and easy to follow.
I work as a Jr. bench tech for an aerospace Co. that builds and repairs inverters for aircraft. This information may help me bring an extra tool to our benches to narrow down harmonic distortions in the equipment. We mostly use simple distortion analyzers, but this FFT math mode may help to actually SEE the frequencies of the harmonics we must eliminate via a tuned trap. Thanks!
Thanks Martin.
doc... harmonics or other sines,,, added on,,,, seems we look at many sines,,, edge on.. 90 degrees from normal view,, huh
great video and hes pretty cool
Thanks a lot man
Thanks for that very helpfull
easy setup
do you have a facebook account or another social media, so that I can ask more something to you about spectrum analyzer?
I need your help
💐💐💐
Explain to your followers what FFT means.....
🙏🙏🌹🌹
maybe you should videolink or paste that follow up video.?
or people shall go on your channel and search for what "FFT on different scopes" and then try to conclude a somewhat date?
Go no idea what this video is that you keep talking about, where you would compare different FFT on different scopes..??
if you never made that video, then put a god dang notice.
Stay off the drugs, you will be okay, trust me.
Thank you Very much sir. It was very helpful for FFT Analysis.
Refresher Course for me! Thank you for the refresh course. KC5WS old 81 yr. old engineer!
Thank you very much for your teaching efforts. Great motivation for me!
Bad explanation...👎
Is there a cheap spectrum analyzer for audio frequencies?
why is DB like talking in a foreign language?
Great! Than you! What software do you recommend for analog audio signals up to 18, 20 Khz?
Kindly gave to you. Must be nice.
Very informative Martin.. I just bought the SDS1102CML from Siglent and want to get the most from its FFT performance. I will be watching your follow up video.
I work on a drilling rig. I'm having some issues offshore in profibus networks & believe it's due to harmonics created from IGBT gate drives, somehow propagating to the comms network. Your explanation is excellent & im looking forward to more!
This video is awesome..very nicely explained. Can you please also illustrate FFT Phase using Agilent scopes, I'm really looking for how to analyze Phase FFT using Agilent oscilloscope.
Are you sure about this statement at 7:30 that -80dB is 10^-9 and -100dB is 10^-11. In my understanding it should be 10^-8 and 10^-10 instead. Am I wrong?
Thanks for your video between you and Alan I have a lot better understanding of my Scope/FFT and my Spectrum analyzer.
which spectrum analyzer is recommended for identifying chemical elements of a material (by optical, by thermal, ...)?
Just Perfection, I have learned how to use a spectrum analyser within around 1 hour. No more commend, thank you very much.
thank u very much !! lots of information theoretically and best part practically.
thank you, very informative.
Mj, when will there be a follow up, if not already done. I can't seem to find it....
awesome !! thanks .. looking forward to this series !!
you are making my day a awsome ... 🖒😆