Products > Test Equipment
Siglent SDG1032X - Sweep does steps of frequency
gf:
--- Quote from: nctnico on June 02, 2024, 06:41:04 pm ---No, it really is you who is wrong all the time.
A sweep is a simple formula: output = amplitude * sin (f * t * ω)
t is incremented for each sample interval as a fraction of ω, f is incremented for each sample interval to create the sweep from the start to end frequency. If you look carefully at the formula, you'll notice that you won't get a full cycle for any of the freqencies at all when f is not constant.
--- End quote ---
Exactly. For details, see also https://en.wikipedia.org/wiki/Chirp
2N3055:
--- Quote from: nctnico on June 02, 2024, 06:41:04 pm ---No, it really is you who is wrong all the time.
A sweep is a simple formula: output = amplitude * sin (f * t * ω)
t is incremented for each sample interval as a fraction of ω, f is incremented for each sample interval to create the sweep from the start to end frequency. If you look carefully at the formula, you'll notice that you won't get a full cycle for any of the freqencies at all when f is not constant.
--- End quote ---
Create 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...
eTobey:
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 pm ---Create 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.
--- End quote ---
I see no contribution here from you, so you can either contribute by giving explanations or answers in a useful and understandable way, or just dont write anything at all.
gf:
--- Quote from: 2N3055 on June 02, 2024, 06:45:07 pm ---Create 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.
--- End quote ---
A 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 a Chirp 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.
gf:
--- Quote from: eTobey on June 02, 2024, 07:37:50 am ---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.)
--- End quote ---
1) 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 measure instantaneous frequency, but it attempts to find full periods in the time domain and reports 1/duration_of_period.
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