[time-nuts] OT - Portable Digital 'scope

[David]

If the bandwidth is really limited to 2 MHz, that is a rise and fall
time of 175ns.  Some of those PPS signals are barely wider than that.

On Thu, 23 Feb 2012 22:26:47 +0100, Azelio Boriani
<azelio.boriani at screen.it> wrote:

>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
>> 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?
>>
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