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| Siglent SDG1032X sine distortion at 1 kHz ? |
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| Martin72:
--- Quote ---So if someone ask/hope that Siglent implement automatic THD measurement.... please do not. Garbage in leads always to garbage out and this garbage we do not need --- End quote --- If you (or others) can figure out why the scope is outputting "wrong" harmonics (only in amplitude?), then the THD feature for the FFT function would be one of the most useful features ever. I know far too little about FFT, but my little layman's understanding finds it remarkable that the higher harmonics look almost mirrored. It would be interesting to see what our HDO6034A "makes" of the signal with its SA function. Unfortunately I am on holiday... 8) |
| rf-loop:
--- Quote from: Martin72 on December 27, 2022, 03:39:49 pm --- --- Quote ---So if someone ask/hope that Siglent implement automatic THD measurement.... please do not. Garbage in leads always to garbage out and this garbage we do not need --- End quote --- If you (or others) can figure out why the scope is outputting "wrong" harmonics (only in amplitude?), then the THD feature for the FFT function would be one of the most useful features ever. I know far too little about FFT, but my little layman's understanding finds it remarkable that the higher harmonics look almost mirrored. It would be interesting to see what our HDO6034A "makes" of the signal with its SA function. Unfortunately I am on holiday... 8) --- End quote --- Example in my last image FFT full span is 25MHz. Only over 25MHz signals are mirrored. Of course if there is (ref my image) 49.992 MHz signal it is then displayed as 8kHz and same if there is 50.008MHz signal and so on but using SA I believe these are produced mainly inside SDS unfortunately. With SA I can not find anything what explain these when I look SDG output. Because explanation is not there in SDG signal, then, imho, one possible guilty is oscilloscope. Do you think SDG generate these when it is set for 1kHz sine. With spectrum there can see one bit higher spur at 16.4MHz but even it is still inside FFT span and its level is around -85dBm and other spurs are more weak least up to 200MHz. |
| mawyatt:
--- Quote from: rf-loop on December 27, 2022, 02:35:28 pm --- Then other thing. SSA specs start 9Khz. Using SSA trace B, I have done some kind of "level correction" curve. Yes this is not now rocket science... only just for fun and make SDS FFT bit questionable for this purpose. Look these "harmonics" in SDS image specially after 7th . What generate these all peaks. It is sure they do not come from generator - least not even close this level. This requires further research. It also requires different methods and tools. --- End quote --- We must remember that the DSO FFT is created from data gathered from the ADC, be it 8, 10 or 12 bit core. Whereas the SA is from a swept type measurement. Recall most SA that use the swept mode also feature a log amp which has a large DR, more so than conventional linear amps, and possible input scaling after the passive LPF or BPF in the signal processing chain. Also, the FFT is not benefiting from the dynamic scaling like we see with the FRA/Bode modes of these DSOs, it just the preamp and ADC at a fixed scale factor, and thus limited by such since the "log" dB scale is just a computation from the ADC raw data and not "preprocessed" before ADC conversion like the Log Amps & Scaling in a conventional SA. I'm not surprised the FFT shows additional "artifacts" & various different harmonic levels over the conventional SA with it's swept capability. Agree, the THD may not be an attractive added feature for signals with low THD, likely limited to something on the order of the core ADC and input amplifier linearity, so maybe 40~50dB, and thus not very attractive for any low level distortion characterization. Like the use of the Trace B correction display to revel the error when the SA is operated below the lower frequency spec limit :-+ Edit: Should also add that these signals in question here originate from a 14 or 16 bit core DAC, whereas the DSO has a 8, 10 or 12 bit core ADC. In signal processing terms this is bass-ackwards (old engineering term to highlight a backwards condition ;D ), the measurement should have a higher effective resolution/precision than the signal of interest if one expects the results to be meaningfull regarding the "quality" of the original signal. Best |
| Martin72:
--- Quote ---Like the use of the Trace B correction display to revel the error when the SA is operated below the lower frequency spec limit --- End quote --- You could also choose a frequency that is in the range, 10khz for example. |
| mawyatt:
--- Quote from: Calvin on December 27, 2022, 02:42:41 pm ---Hi, just a number of quickn´dirty measurements of my SDG2042X with my QuantAsylum QA401 24Bit audio analyzer. Yellow traces are from the analyzer, red traces from the SDG2042X. Frequencies: 1kHz and 100Hz, Amplitude: 0dBV (note the analyzer´s ADC has its THD-minimum at -16dBV input level) It shows that the analyzer´s own generator creates a cleaner Signal and at lower noise due to much lower bandwidth. regards Calvin --- End quote --- Did some similar tests over here at 10KHz with Pico Scope which has a 16 bit ADC. https://www.eevblog.com/forum/testgear/comparison-between-siglent-sdg1000x-and-2000x/25/ Best, |
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