182 N5511A Phase Noise Test System User’s GuideResidual and Additive Noise Measurement FundamentalsCalibrating the MeasurementDouble-Sided SpurThis calibration option has the following requirements:— One of the input frequency sources must be capable of being phasemodulated.— The resultant sideband spurs from the phase modulation must haveamplitudes that are -100 dB and -20 dB relative to the carrier amplitude.— The offset frequency or modulation frequency must be between 10 Hz andmaximum (See the "Measured beat note" section on page 87).Advantages— Requires only one RF source.— Calibration is done under actual measurement conditions so allnon-linearities and harmonics of the phase detector are calibrated out.Disadvantages— Requires RF source used to have modulation capabilities else a phasemodulator which operates at the desired carrier frequency.— Requires audio calibration source.— Requires RF spectrum analyzer for manual measurement of ΦM sidebandsor preferably a modulation analyzer.For a dual-sided spur cal, turn on phase modulation on the stimulus to create anarrowband sideband at a known amplitude and offset relative to the carrier.Enter the offset and level in the Known Spur Parameters section in the Cal tabof the Define Measurement menu.Figure 7-12 Known Spur ParametersBecause the calibration is performed under actual measurement conditions, the Double-sidedSpur Method and the Single-sided Spur Method are the two most accurate calibration methods.Most phase modulators are typically narrow-band devices; therefore, a wide range of testfrequencies may require multiple phase modulator.
