NIST Technical Note 1337: Characterization of Clocks and Oscillators

7. PHASE NOISE AND AM NOISE MEASUREMENTS 277(7) The discriminator calibration factor is calculated in hertz per volt asCF = mfml...;2 v'ms = 2.405fmli2 v,ms· (91 )The modulation index m for the first Bessel null as used in this techniqueis 2.405. The modulation frequency is j~.3. .\leasurement and Data PlottingAfter the discriminator is calibrated, the modulated signal source is replacedwith the frequency source to be measured. Quadrature of the signalsinto the mixer is reestablished, attenuator No.4 (Fig. 20) is set to 0 dB, andthe measurement process can begin.The measurements, calculations, and data plotting are completely automated.The calculator program selects the Fourier frequency, performsautoranging, and sets the bandwidth, and measurements of Fourier frequencypower are performed by the tracking spectrum analyzer. Each Fourierfrequency noise-power reading P n (dBm) is converted to the correspondingrms voltage byThe rms frequency fluctuations are calculated as(92)l5v rms = V lrms X CF. (93)The spectral density of frequency fluctuations in hertz squared per hertz iscalculated aswhere B is the measured IF noise-power bandwidth of the spectrum analyzer.The spectral density of phase fluctuations in radians squared per hertz iscalculated asThe NBS-designated spectral density in decibels (carrier) per hertz is calculatedasSpectral density is plotted in real time in our program. However, the datacan be stored and the desired spectral density can be plotted in other forms.Integrated phase noise can be obtained as desired.(94)(95)(96)TN-228