The first thing I noted was the seemingly random usage of window functions. Hanning and Gaussian are not comparable and for a meaningful test we should stick with the Flattop window on both instruments.
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I was aware about that but the focus was on spurious so I spent very little time on that so I chose the window type on the base of the peak shape well knowing to be in "uncal" condition, but to be honest ... i do not know how to select flattop on SA ... you sure it's possible with my model ? (SSA3021X)
I understand. Flattop is the default window on every general purpose SA, because amplitude accuracy and dynamic range (side lobe suppression) are the most important criteria. Most have some additional window (Gaussian, Nutall) and a few have even more to choose from. But for continuous signal analysis, where we can acquire plenty of data, the Flattop window is the obvious choice.
Watched Dave's recent Rigol DHO800 review, the connector SNAFU and the oops retraction. Part of this video he is comparing with a low end Siglent off and on. Puts it in a bad light but I assume that was because he was beating the price drum.
Yeah, some time ago I’ve analysed the FFT part and thoroughly disproved any unwarranted claims about the inferiority of the old little Siglent (reply #200):
https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/200/Channel 1 & 2 fed with a 1MHz 0dBm sinewave. Math used to add both channels. FFT then ran on the math channel. This is about the limit of the old LeCroy. It can display the separate peaks but the readouts will only display a single peak. Again, wrong tool for the job but I am curious how well your scopes can resolve two peaks like this. Feel free to use an external combiner rather than the math.
I assume you meant two sine waves with close to 1 MHz frequency. Using the math channel for adding the two signals is a great way to simplify the cabling and avoid the 6 dB insertion loss.
The SDS9824X HD does a reasonable job; its Marker Table doesn’t have the necessary frequency resolution and accuracy is generally poor because of the cheap 25 ppm quartz timebase (and it shows), but here you go:
SDS824X HD_FFT_1MHz_Span500Hz_d5Hz
In the above screenshot, a 999995 Hz sine was combined with a 1 MHz sine, hence the difference between the two signals is 5 Hz. The two signals are just distinguishable on the screen, and peaks search had to be configured for 12 dB excursion (instead of the 20 dB default) in order to find the two separate peaks. As mentioned before, Frequency resolution is insufficient, but at least the level accuracy is nothing to complain about.
An SA would be better suited for such extreme use cases, but if it has to be a DSO, then why do I even try to compete with an upper midrange instrument from LeCroy by using a low-end entry-level device like the SDS800X HD? (Answer: because this is a thread about the SDS800X HD)
The vintage of a LeCroy isn’t really important in this context. The extreme applications demonstrated here certainly exceed the capabilities of many other expensive scopes – but not for a midrange LeCroy, no matter how old it is.
With all that said, I pull out a worthy contender for a change:
SDS7404A H12_FFT_1MHz_Span100Hz_d0.5Hz
In the above screenshot, a 999999.5 Hz sine was combined with a 1.0000000 MHz sine, hence the difference between the two signals is 0.5 Hz or 0.5 ppm. The two peaks are just distinguishable on the screen, and excursion for peaks search could be more than 50 dB. Displayed frequency resolution is sufficient here, but the actual resolution is not, as the 0.5 Hz is displayed as 0.79 Hz. Frequency accuracy is in the realm of 1 ppm and amplitude accuracy better than 0.15 dB in this scenario.