Hi Aldo,
Thanks for the reply and information.
From your screenshots, the small signal response looks fine to me. Small jitter in the signal is to be expected.
That clears out any internal constrains concerning the bandwidth upper limit on small signals.
Excellent!
I would say that we would need to spend way more to get better results.
So the 5 MHz limitation is only related to the probes included in the package.
The nominal 6 MHz LPB at X1 of similar probes is close enough to the specified 5 MHz for the scope on X1 seen in the user guide.
Looking closer to published pictures of the older PCB versions (where there is no soldered metal shield over the vertical input section), I have a rough idea on what they have designed.
Initially I assumed that a dedicated small signal amplifier was in use to handle the mV range, but after your test results I do not think they did it in that way (still it is used in more elaborated and expensive devices).
In fact it seems they did better than that for this product price range, despite the average/poor input sensitivity of 10mV/div that in fact points to the probable design choice in use.
More likely the vertical amplifier/attenuator is a single circuit handling all the vertical sensitivity levels, kind of a PGA (programmable gain amplifier), managed by the MCU (F1C100S AllWinner Tech SoC ARM926EJ-S) IC that controls one 3-to-8 decoder (SM74HC595D) IC per vertical channel. These SM74HC595D decoders seems to be acting as control lines actuating on the PGA section level selectors.
Unfortunately the Chinese plant decided to keep three crucial IC's identification a secret, by erasing the silkscreen labels of them.
Two of these IC's (16-pin) are used in the vertical PGA section (one per channel) and these make sense to be analog PGA devices.
The 3rd one being the ADC IC (48-pin) that other members have mentioned above as likely being an AD9288 or compatible device.
As others commented above, marketing the scope as running at 500 MSPS is strange to say the least, as a single AD9288 is able to run at 100 MSPS per ADC channel with a total of 200 MSPS.
200 MSPS would be the absolut minimum to reconstruct a sinusoide at 100 MHz in one vertical channel as clamed by the manufacturer.
Using both vertical channels leaves just 100 MSPS per channel and this would allow to read up to 50 MHz at most.
This is not far from what the scope manufacturer specifies.
Either the ADC IC is a custom Chinese IC able to run at 500 MSPS (based on AD9288 or not) and the claim is correct, or else if it is a genuine/cloned AD9288, then it looks highly improbable, even with overclocking, to run the IC at the claimed rates.
I will dismantle my unit after it arrives to have a more detailed look and try some sort of reverse engineering, as I usually do for all my acquired devices, specially when the manufacturer do not release service documentation.
Unrelated talk:
I have used professional scopes since my days in school in the 70's and have worked professionally in electronics as used in several lab environments including medicine investigation, telecommunications (RACAL, STORNO, FURUNO, DECCA, REDIFON, RCA, and a few other brands), and later doing computer hardware maintenance in the 80's, so I am familiar with a few generations of scopes, most of them from Tektronix and HP, well before the DSO generation.
Then I moved to computer software and forgot my electronics background for a while, but kept my radio and calculator collector hobby.
Currently I have a couple of scopes for my private usage, one being a CENTRAD from the 70's (100% analog, CRT, transistorized with a few TTL chips), and more recently I acquired a Owon SDS1102 DSO and a FeelElec FY6900 signal generator.
In order to check, align and repair my collection of radios, mainly classic analog and a few DSP based as well, I use a vintage HEATHKIT IG-102S signal generator (valve based) and a classic, vintage, professional, FLUKE 1920A frequency counter.
See, I would need a clean and low signal level generator, in the range of a few micro-Volt and below (0.2uV), to inject at the different receiver stages, and for that I managed to use the HEATHKIT despite it is not a professional equipment, missing a calibrated output attenuator (I use a diy ladder attenuator, not calibrated).
The modern FeelElec FY6900 looks good in the specs, but the signal output levels are more oriented to digital and analog high level signal devices.
Finally, I miss the 500 MHz Tektronix I used in my telecomm workshop in the 70's to be able to read low level analog signals from my double-conversion heterodyne radios, where the 1st IF frequency is on the 40 to 60 MHz range.
The Owon SDS1102 is almost able to do the job (it can read the local oscillators because of the highish signal levels), but I really would need a 200 MHz wideband with something like 1mV per division to do proper readings.
Why now this tiny cheap ZEEWEII DSO2512G ?
Well, I like to collect and analyse electronic devices, specially small ones in my spare time.