12 and 16-bit oscilloscopes

I wonder if picotech ever fixed the glaring bugs in their software?

My boss bought a ADC-216 when we needed an 50KHz spectrum analyser. I'd seen picotech equipment before and reccommended buying a spectrum analyser off ebay instead. When the picotech unit arrived I connected it in parallel with a conventional scope and tried it out.

I found several serious software bugs. I can't remember them all now. It has an AC voltmeter function, the spec page claims 1% accuracy. It worked ok up to about 10KHz and above that the reading were completly wrong. The hardware is just a fast ADC so the PC software did the task of adding up the area of the voltage versus time graph.

A picotech support person reproduced the problems I found and promised to send a new version of the software. Months later after a few reminders they finally emailed me some software, the same buggy software I'd already been supplied with the unit.

Bob

[edit discouraging story]

Bummer. Now I'm disinclined to buy one.

Any other experiences out there?

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Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.

I've purchased and used ADC216 specifically for the dynamic range in fft mode. For this purpose it seemed very usefull to me and I was able to troubleshoot a few things I could never have done without it. Although I can't and did not compare its operation against any other comparable unit.

I admit to not having used it as a scope, analogue scope is a much better solution for that.

SioL

Well, it won't fit in your "under $1500" budget, but HP/Agilent for many years has been making a 23-bit 20Ms/s card. It's not necessarily useful to 23 bits, but even by today's standards, the distortion and spur performance isn't too shabby, and was certainly cutting-edge when it was introduced. And in a stand-alone instrument, the HP/Agilent

89410, especially those made around 2001 and later, should give you pretty nice performance out to 10MHz. I can "see" signals 120dB below full scale with a dB or so accuracy with mine, if there aren't also big signals that put distortion products on top of them. There are a very few spurs that keep you from getting to that low a level at every frequency, but they are pretty low amplitude and few in number. (We'd all love to have 120dB of spur-and-distortion-free dynamic range in a 10MHz bandwidth analyzer with general-purpose inputs, but it's not likely to happen this year...)

Cheers, Tom

You can get the HP3562A used for under a grand. It is 14 bits and

100khz. It has GPIB to offload the data.

snipped-for-privacy@sushi.com wrote: ...

Should note it's 100kHz bandwidth; sampling is faster. Of course, it's also BIG and HEAVY (and if something goes wrong inside, it may not be easy to fix).

It has a self-check, which makes the used purchase safer. The big advantage to the 3562 is the synchromized sine source. No edge effects, i.e. windowing errors. Big? You bet. ;-)

I do have a 3563A which is the 16bit that followed the 3562A. Big and noisy (fan) but excellent.

The 3562A has service manuals available but I couldn't find the 3563A ones.

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Thanks,
Fred.

s=2E

Gee, Fred, I'm curious where you found a 16 bit 3563A ... ;-)

Cheers, Tom

s=2E

Are there 3562 manuals on line?

I have them in case you can't find them, but I guess I got them either from the agilent web site, either from their ftp.

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Thanks,
Fred.

t's

s,

ones.

ftp://ftp.agilent.com/pub/manuals/ I found them. Thanks.

Hi Tom, Did you have the curiosity of checking exactly the accuracy ? Below 100dB is quite difficult to claim 1dB accuracy, even with a

45.000$ VNA or spectrum analyzer.

greetings, Vasile

Hi Vasile,

Well, yes, it was a bit more than idle curiosity. :-) The linearity of the ones with new ADC boards is generally quite good, noticably better than the ones with the older boards, and those weren't bad at all. Linearity to that level is not guaranteed, though. As you say, it's not trivial to test.

Cheers, Tom

How about a different approach? semi-pro and pro audio offers some interesting prospects, such as 10 channels at 24 bits and 192 ksamples /s. requires firewire/1394 or usb2. start with RME/hammerfall please.

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 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

and pro audio offers some

One thing to be a little careful about with cards that are designed to digitize audio is that they may use ADCs which indeed output 192k samples per second, but which have internal digital filters which will NOT allow response beyond 1/4 the output sample rate, or thereabouts. If the design of the board has limits in the analog signal path, you may be able to bypass that, but it will be difficult to deal with an ADC like that. In doing a survey of ADCs for such an application, I found more than one that was unacceptable for that reason. I believe a few also have highpass filters that would prevent them from going to DC, and in any event you might have to hack the software to disable such a filter. If you want a highpass, it's nice to do it digitally, because you can insure zero offset voltage, and many high-end audio ADCs have at least the ability to do it in their digital processing. (Practically all audio ADCs these days are delta-sigma type, with a lot of digital filtering and decimation going on inside.)

Cheers, Tom

[...snip good info]

Can you tell us which boards had response to DC?

Which ones would you recommend for an inexpensive low-end pc scope?

Regards,

Mike Monett

Hi Mike,

Sorry if I wasn't clear about that. I was doing a survey (and not a terribly complete one at that) of high resolution ADC parts that would be useful in a digitizer that went to at least 80kHz bandwidth. I can't tell you about any of the boards; I don't have info on what ADCs they actually used. There may be good reasons to sample audio faster than 44.1ks/s, but extending the digitized bandwidth much beyond 20kHz is probably not very high on the list.

Cheers, Tom

I would love to make a "scope" based on something like the AD7660. It's a 24 bit 2.5MHz sigma delta ADC .

I was thinking

- USB powered

- buffer data in local SDRAM

- Hi-speed USB interface

- local SDRAM chip to buffer samples

- *all* samples streamed to controller PC

- PC does post processing for "triggering", averaging, spectrum analysis

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John Devereux