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  1. #1
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    Phase Noise Measurement using spectrum analyzer (PLL technique)

    Hello,

    I am planning to measure the phase noise of a VCO using PLL technique using spectrum analyzer model # R&S FSL (9kHz - 3GHz).

    My question is what should i look for in the spectrum analyzer for measuring the phase noise. Do I need to plot the output of the LPF (connected at the output of the mixer) from 9kHz to, say, 100kHz? Then the resulting display will give me the rms value of the mixer output (amplified by a LNA), at different frequencies. Will it give me the phase noise once I divide the measured rms values from the display by the calibration constant, Kd? (Kd is the zero-crossing slope of the low pass Filter's output, which is the proportionality constant between phase noise of the oscillator under test and rms voltage measured at the LPF output)

    Or will I have to set a center frequency, say, at 10kHz and span, say 2kHz, then I measure the signal rms power and divide it by the span to get the rms value per Hz. And then repeat it by changing the center frequency. Then calculating the phase noise from the rms value measurements using the zero-crossing slope calibration. And finally plotting the values at each frequency in MATLAB to get the phase noise vs frequency plot?


    Thanks in advance,

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  2. #2
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    Re: Phase Noise Measurement using spectrum analyzer (PLL technique)

    You can measure PN with Spectrum Analyzer but it won't be very healthy.Although modern Signal Analyzers have Phase Noise Measurement Features, I'd prefer use a Phase Noise Analyzer for better results..



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