[time-nuts] OT - Portable Digital 'scope

[Attila Kinali]

On Thu, 23 Feb 2012 20:01:18 -0000
"Rob Kimberley" <robkimberley at btinternet.com> wrote:

> I'm looking at Item: 300658066641 on EBay, and wanted to know if anyone in
> the group had any experience of this product. I know this is way off topic,
> but as a group it's nice to know what's out there and possibly useful in our
> mutual hobby.

It depends what you want to use it for. If you just want to have
something protable that can show you roughly what's going on,
then this might be a good thing. For anything else, especially measurements,
i wouldnt trust it further than i can throw it.

It's actually quite nice that they put the schematics online too,
so their claims can be verified.

First that jumps out is that they are using a AD9288-40 as ADC.
Note the -40 there? It means it's an 40Msps ADC. Ie the maximum
usable BW you can have is 20MHz (actually a bit lower). The analog
circuitry doesn't seem too bright either, but i guess you should be
able to get the 20MHz. I havent checked the exact circuitry so
i cannot say whether the input circuit does filter at 20MHz. But
as they claim to have 72MHz analog bandwidth, i would be very carefull
about aliasing problems

The input circuitry isn't very impressive either and has an undefined
input capacitance (there is a trimmer there) somwhere between 5pF and 30pF
(plus stray capacitances). I find it a it strange, that they disconnect one
input of the frontend opamp... it might anything from going into saturation
to start bouncing around... 
The analog switches are rather on the cheap side, nothing you'd expect
in an DSO, but well.. for that price :-)

Also notice that the connectors used look like SMB or MCX antenna
connectors. Ie those would not be able to withstand many mating/break
cycles.

Overall, i'd say a good portable gauge, but not much more.

For a more indepth analysis i'd have to take the schematics apart
into a readable format... 

			Attila Kinali

-- 
Why does it take years to find the answers to
the questions one should have asked long ago?