[time-nuts] OT - Portable Digital 'scope
azelio.boriani at screen.it
Thu Feb 23 21:26:47 UTC 2012
Yes, in my opinion the connectors are MCX and I totally agree with Attila
about the 20MHz limit. Nice toy to just take a look at low speed signals,
for example GPSDOs 10MHz and PPS, serial lines and so on.
On Thu, Feb 23, 2012 at 9:49 PM, Attila Kinali <attila at kinali.ch> wrote:
> 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
> > the group had any experience of this product. I know this is way off
> > but as a group it's nice to know what's out there and possibly useful in
> > 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
> 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
> 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?
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