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Is wraparound possible on PS3206D

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Is wraparound possible on PS3206D

Postby wpats » Wed Jul 08, 2015 1:01 am

Hi,

I have been observing pulsed RF signals which are fed to a negative polarity diode detector whose output is hooked up to the scope input. Until now, as expected the output of the detector is always a negative voltage envelope. Now I am seeing the scope display show positive spikes. Is it possible that this is a result of the 12 bit ADC output wrapping around from minimum (negative) value to positive value ? I have observed in other situations where I set the vertical sensitivity too small and the input signal exceeds the maximum displayable it shows a red '!' overflow indication.

Is it possible that in my latest observations the value has wrapped around so the scope (or the Picoscope software, whichever does overflow detection) does not know that there is an overflow ? The other possibility is that the diode detector is breaking down but that is unlikely given the small amplitude of the input signal.

Thanks for any info,

--Patrick
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Re: Is wraparound possible on PS3206D

Postby Martyn » Tue Jul 14, 2015 10:14 am

Can you post some pictures, or preferably a psdata file, then we may be able to say what is happening.
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Re: Is wraparound possible on PS3206D

Postby wpats » Fri Jul 17, 2015 9:20 am

Hi Martyn,

Here is a sample of what I am talking about. The psdata file size is above your upload size limit so I've included a screen shot. The blue channel input is from a high frequency antenna connected to a negative polarity Schottky diode detector. The negative spikes are Wifi signals in the 2.4GHz band from my computer/router and these are what I normally observe. But notice there are positive spikes in this capture which may be due to wraparound. Or that is one possible theory. The other possibility is that the diode detector is breaking down but that is unlikely given that the input is from a small antenna which cannot produce enough power to cause breakdown.

Also notice that all the positive spikes have the same amplitude which makes it unlikely that they are random noise. The other data point is that for this observation I enclosed the Picoscope in a plastic enclosure and left it running for several hours which would have caused the temperature to rise. Could this be a thermal effect ?

I would appreciate any help/explanation.

Thanks,

--Patrick
Attachments
Wraparound.JPG
Screenshot of possible wraparound.
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Re: Is wraparound possible on PS3206D

Postby Martyn » Fri Jul 17, 2015 10:44 am

The values are in range, so they look like real values, I need to see the data file to comment further.

Can you save just one waveform buffer, File->Save and then select Current Waveform, as a psdata file and upload that, it should be small enough.
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Re: Is wraparound possible on PS3206D

Postby wpats » Thu Aug 27, 2015 8:36 pm

Hi Martyn,

Sorry for the delayed response. A single waveform capture is also above your upload limit. So I have put the file on dropbox at the following link: https://www.dropbox.com/s/kpfj68r22xvplfa/Sample1.psdata?dl=0. Please take a look and let me know what you find.

Thanks for the help,

--Patrick
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Re: Is wraparound possible on PS3206D

Postby Martyn » Fri Aug 28, 2015 9:37 am

There is something wrong with the way the data is being pulled from the psdata file to the display. If you resize the window you can see the spikes appear and disappear, both above and below the main trace. However if you put a measurement on showing the maximum value, this does not change.

This has been raised as an issue with the development team.
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