Siglent SDG1032X - Sweep does steps of frequency - Page 1
Forum section: electronics / testgear

author: eTobey
author_rank: Super Contributor
timestamp: June 02, 2024, 07:37:50 am
content: On the picture, you can see, that in the beginning, the frequency is constant for about 1s. (notice the constant artefacts, that show a constant frequency from '-1s' to '0s')It is a 3s sweep from 100Hz to 30MHz.Is this a normal behaviour of such devices? I would have expected the frequency to rise without steps.(Yes, i know, its a noobish question, but i accidently posted it in the wrong section, and cant delete it.)

author: 2N3055
author_rank: Super Contributor
timestamp: June 02, 2024, 08:49:37 am
content: Quote from: eTobey on June 02, 2024, 07:37:50 amI have an advice for you.Every time you have a problem like this, ask yourself what did you expect to happen. And how would you do it if you were to make a such device.Let's turn the thing upside down. From 100Hz to 30MHz in 3 seconds....Is it log or linear sweep?If linear, that is roughly 10MHz/s sweep.At time:zero +1s you are at 10MHz (100ns period)zero +100ms you are at 1MHz (1µs period)zero +10ms you are at 100Khz....Wait...At zero+10ms you are still at first period of 100Hz .... hm...How can it beeee... Maybe we cannot ask AWG to generate mathematically/physically impossible frequencies....

author: eTobey
author_rank: Super Contributor
timestamp: June 02, 2024, 09:32:02 am
content: Its a log sweep.I dont understand what you try to explain. I can not imagine impossible frequencys, apart from 0 or negative ones.

author: nctnico
author_rank: Super Contributor
timestamp: June 02, 2024, 09:38:10 am
content: Quote from: eTobey on June 02, 2024, 09:32:02 amLog sweeps are typically implemented as a series of steps on AWGs and thus skipping frequencies. This can lead to rather odd results like partial sine waves at low frequencies. But still, I would expect the image to show a more constant amplitude. Did you turn peak-detect on on the scope and use a BNC cable?

author: 2N3055
author_rank: Super Contributor
timestamp: June 02, 2024, 09:45:07 am
content: Quote from: eTobey on June 02, 2024, 09:32:02 amAre you one of those people that think that if you can write something in a mathematical formula then it has to exist in physical world?Please create me 100Hz signal that lasts 100ns.

author: nctnico
author_rank: Super Contributor
timestamp: June 02, 2024, 09:57:59 am
content: Quote from: 2N3055 on June 02, 2024, 09:45:07 amYou are wrong here. You can easely create part of a 100Hz sine wave which lasts 100ns. You just won't get a full cycle (as math dictates). And that is exactly what an AWG will do when instructed to make a sweep. During linear sweep, the frequency will be varied continuously (resulting in creating only small fractions of sine waves at low frequencies; but still mathematically correct). Log sweeps are more difficult to implement on an AWG and many will output frequency bursts (containing partial waves for low frequencies) to step through the frequencies and thus skipping frequencies.

author: Joe1vm
author_rank: Newbie
timestamp: June 02, 2024, 03:11:57 pm
content: Hi.It looks familiar.....https://www.eevblog.com/forum/testgear/siglent-sdg1000x-waveform-generators/msg5288380/#msg5288380But I still can not understand such amplitude variation across frequency range....

author: eTobey
author_rank: Super Contributor
timestamp: June 02, 2024, 03:34:48 pm
content: Quote from: 2N3055 on June 02, 2024, 09:45:07 amThought about just creating it for you, but then thought, na, you are not worth it...Quote from: Joe1vm on June 02, 2024, 03:11:57 pmThis variation is coming from a little circuit, but thats of no relevance.

author: KungFuJosh
author_rank: Super Contributor
timestamp: June 02, 2024, 04:06:44 pm
content: In case you don't know, this is the thread for that AWG where all the topics actually belong:https://www.eevblog.com/forum/testgear/siglent-sdg1000x-waveform-generators/

author: 2N3055
author_rank: Super Contributor
timestamp: June 02, 2024, 05:57:21 pm
content: Quote from: eTobey on June 02, 2024, 03:34:48 pmFamiliar ??Again both Nico and you didn't understand a single thing, but it never stopped you (or him) from being wrong...

author: gf
author_rank: Super Contributor
timestamp: June 02, 2024, 06:44:05 pm
content: Quote from: nctnico on June 02, 2024, 06:41:04 pmExactly. For details, see alsohttps://en.wikipedia.org/wiki/Chirp

author: 2N3055
author_rank: Super Contributor
timestamp: June 02, 2024, 06:45:07 pm
content: Quote from: nctnico on June 02, 2024, 06:41:04 pmCreate that chirp (it is not a sweep) and feed it into scope, do a FFT and tell me what you see?There is a reason when we do sweep that we actually specify dwell time at frequency to enable time for equipment to detect the frequency in full amplitude.Frequency chirp are usefull but for other things like radars...

author: eTobey
author_rank: Super Contributor
timestamp: June 02, 2024, 07:48:37 pm
content: I asked a question here, that you did not really answer. Your answer was more offending than satisfying.Quote from: 2N3055 on June 02, 2024, 06:45:07 pmI see no contribution here from you, so you can either contribute bygiving explanations or answers in a useful and understandable way, or just dont write anything at all.

author: gf
author_rank: Super Contributor
timestamp: June 02, 2024, 07:53:34 pm
content: Quote from: 2N3055 on June 02, 2024, 06:45:07 pmA traditional continuous Glide-Sweep is basically the same as a Chirp.However, many modern spectrum analyzers do a Step-Sweep, measuring a finite number of discrete frequency points.Since you cannot configure the number of discrete frequency points, I would expect that the SDG1000X generates a continuous Glide-Sweep. And where can you configure a dwell time in the SDG1000X? I could not find anything in the manual. IMO that's only relevant for a step-sweeping SA + TG (or for a NA). If you do a Bode Plot, then I do not think that the scope configures the SDG to sweep, but more likely it tunes the SDG to each frequency point individually.If you manage to fit the whole interval of the chirp exactly into the FFT window then you should see aChirp Spectrum. Although the waveform has a constant peak amplitude in the time domain, the spectrum is not flat in the frequency domain, but shows Fresnel ripples.EDIT: If you would do a STFT instead, then you could see the frequency as a function of time in the spectrogram.

author: gf
author_rank: Super Contributor
timestamp: June 02, 2024, 08:26:56 pm
content: Quote from: eTobey on June 02, 2024, 07:37:50 am1) You sweep up to 30 Mhz and use a sample rate of only 20 MSa/s? The signal is undersampled.2) Don't expect the math function Freq() to give reliable results with a chirp/sweep. My understanding is that it does not measureinstantaneous frequency, but it attempts to find full periods in the time domain and reports 1/duration_of_period.

author: 2N3055
author_rank: Super Contributor
timestamp: June 02, 2024, 09:13:06 pm
content: Quote from: gf on June 02, 2024, 07:53:34 pm1000X cannot do dwell.Fast continuous glide sweep will create linear chirp.In Bode Plot there are discrete frequencies stepping, you are right.IF you manage to fit whole chirp exactly into window you WILL get Chirp spectrum.You will not get same result as people expect to see with slow sweep and FFT in peak hold mode.That is why I said not to confuse chirp burst with frequency sweep. I wanted to point out that our equipment need time to detect frequency with sufficient amplitude to be actually detected, and to have enough time to achieve full amplitude for us to be able to verify the right amplitude. Which is what you do when you sweep. So it is either dwell or slow enough so window can grab enough energy in its bin to do the good job. That is if you use FFT. You can simply use long capture and look at it in time domain. Where also you need at least one full period in all frequencies in question to be able to see what was it's P-P amplitude at that frequency.And yes, on 3000xHD and 7000A by using Gated Acquisition you can traverse chirp and see how frequency changes.You can also see frequency change with track plot, but you need to sample properly...