Being back home now (actually been back most of the week, but was busy with other stuff), I decided to check out some more things on the ZT-703S
I still have the original 1.0.9 firmware on mine.
When running in "High" mode, the frequencies output by the generator accessed from the menu (Menu -> left -> F4) are WRONG other than the 1khz probe compensation signal, which is actually correct. In any other output mode though, the frequencies are wrong.
5.0 kHz => is actually 7.0 kHz
2.0 kHz => is actually 2.8 kHz
1.0 kHz => is actually 1.4 kHz
etc etc (same scaling factor of 1.4 is present at all frequencies).
Oddly, using the "other apps -> Gen", the frequencies are correct
But in Sine output mode, it doesn't meet the 2.5Vpp claim at all (more like 2.0Vpp) and above 400kHz, the waveform is very triangular, not sinusoidal. Same can be said for any of the "partial sinusoidal" waveforms - they get very triangular and aren't very sinusoidal.
Going the other way and looking at a signal from an external generator, I see some peculiar aliasing too:
Feed in a 20Mhz sine wave, at 10, 25, and 50ns/div, things look pretty good and the frequency reads correctly. At 100ns/div, the frequency measurement is wrong (probably due to the overall bug at 100ns/div). From 250ns/div through 200us/div things look ok-ish - what you'd expect, the waveform getting more and more "solid" as the timebase is too slow to see any detail in the signal. At some timebases, there is some overall AM-ish distortion of the overall envelope though - definitely some kind of periodic noise, or some kind of aliasing showing up. Then suddenly at 500uS/div, it looks like a pure sinewave again, perfectly triggered and stable, at a much lower frequency, but the frequency measurement shows 0 as it can't measure anything. Definitely misleading if you're looking at an unknown signal and manually moving through timebases to have such an aliased signal appearing.
Comparing the same signal on the Owon HDS2202S, you get none of that at any timebase with the same 20MHz sine signal being fed in - there are some "sinusoidal-ish" aliased signals at very slow timebases on the Owon (5ms/div), but they're not triggered and stable, but rolling, giving a good indication that that's not the true signal, and just an aliasing / sampling artifact.
On an Agilent DSO-X 2024, there is no hint of aliasing or any waveform that resembles a "slower sine" at any timebase right up to and beyond 1S/div.
If you compare sampling rate at timebases, the Agilent scope is using a far higher sampling rate at every timebase compared to the Owon. The ZT-703S doesn't seem to indicate sampling rate vs timebase at all, so it's really hard to know what it's doing.
With the cheap price of the Zoyi, or even the Owon HDS series, and it being potentially many people's "first scopes", they definitely leave a lot of "traps for young players" as Dave would say...
I'm not sure if there's anything else anyone wants me to measure before I upgrade the firmware - turns out I don't currently have a working function generator above 20Mhz, except for potentially with an SDR, or with a VNA not sweeping, but set to a fixed frequency. The wavegen in the DSO-X 2024 only goes to 20Mhz, and my proper RF sig gen needs repairs.