PicoScope 4262 noise floor has significant spurs

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Gerry
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Re: PicoScope 4262 noise floor has significant spurs

Post by Gerry » Fri Jan 25, 2019 5:12 pm

Hi Dan,

The PicoScope 4262 would not have the same sort of front end as the HP analyzer, as the frequency domain processing is not a hardware function (so it is not even a digital spectrum analyzer, i.e. it doesn't capture a spectrum of frequencies and then transform the analogue values of those frequencies into digital values for computation and display), the spectrum is entirely created in software (so the hardware is all time domain only, no log-amps or compensation needed).

Regards,

Gerry
Gerry
Technical Specialist

dnessett
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Re: PicoScope 4262 noise floor has significant spurs

Post by dnessett » Tue Feb 12, 2019 12:26 am

Gerry doesn't seem to be responding. Anyone else know the answer to my question?

Thanks,

Dan

Posted later: Oops. Didn't see Gerry's reply as it was on the second page. My apologies.

Dan

Gerry
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Re: PicoScope 4262 noise floor has significant spurs

Post by Gerry » Tue Feb 12, 2019 10:52 am

Hi Dan,

I had to create a quick answer for you as I was going to be out of the office for a while. So, I've made the below explanation more comprehensive for the benefit of other forum users.

As already mentioned, you have to keep in mind that the Spectrum plot of a PicoScope is not a digital Spectrum Analyzer. It is a mathematical transformation of data captured in the normal way, i.e. the Time domain of an oscilloscope, while a Spectrum Analyzer sweeps a window across the spectrum of a signal in real-time to analyze the content. We can make the analogy that it acts like a digital Spectrum Analyzer because it splits the spectrum up into discrete sections (bins) to convert the information into the frequency domain equivalent, while a Spectrum Analyzer, scanning the spectrum, effectively splits it up into continuous sections to analyze and display the frequency content.

The harmonics of a signal diminish pretty quickly as you increase the number of the harmonic, so the plot of a Spectrum analyzer, or Spectrum mode in an oscilloscope, is most useful when it can bring the higher harmonics into view that would normally be lost off of the bottom of a linear scale, so a logarithmic scale is the preferred way of plotting a frequency spectrum. The Spectrum analyzer therefore uses a log amp for its analysis/plotting, because it is analyzing and plotting the data while it is sweeping across the spectrum. The PicoScope will have already captured the data linearly (using the amplification/attenuation best suited for displaying the chosen input range) and only needs to transform it according to the users requirements, so that it can be displayed in linear or logarithmic form.

Regards,

Gerry
Gerry
Technical Specialist

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