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    Spectrum analyzer and ripple measuring

    Hello

    I have a SMPS and would like to measure ripple and noise from 9Khz to 100Khz using a spectrum analyzer.

    So I have a DSA 875 from Rigol that can measure from 9Khz and up.

    This is the first time I am using a spectrum analyzer and I have no idea what to do. Should I use a capacitor in line (to block the DC) ? I assume that C and R(50R) will make a HPF so I calculated that C should be at least 2.2uF

    I would like the results to be very accurate (uV level).

    •   Alt7th January 2018, 16:13

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    Re: Spectrum analyzer and ripple measuring

    I want to add that ripple should be around 40-60Khz (sw frequency)

    I was thinking to have the sweep time to 10s , RMS detector on and 0 DB attenuation

    RWB at 15Khz , measurements in FFT , VBW at 100Khz

    Bandwidth 9-900Khz



    •   Alt7th January 2018, 21:18

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  3. #3
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    Re: Spectrum analyzer and ripple measuring

    I don't understand how "FFT" comes into play. DSA875 is classical sweeping spectrum analyzer, no FFT involved.

    According to datasheet, the RF input is already DC coupled with 50 V DC rating. So you won't need another DC block for lower DC voltage range. I would however set an input attenuation of 20 or 30 dB to achieve maximum strength against transients. If the switching noise is very low (unlikely), you can later increase the sensitivity.


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    •   Alt11th January 2018, 17:16

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    Re: Spectrum analyzer and ripple measuring

    Hi

    thx you for yoour help , I am able to take readings. I used rbw at 10Khz and vbw at 100Khz and sweep time 10s



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