Keysight Technologies N5511A, Руководство пользователя

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260 N5511A Phase Noise Test System User’s Guide
AM Noise Measurement Fundamentals
Calibration and Measurement General Guidelines
Calibration and Measurement General Guidelines
— Although AM noise measurements are less vulnerable than residual
phase-noise measurements to noise induced by vibration and temperature
fluctuation, care should be taken to ensure that all connections are tight
and that all cables are electrically sound.
— The noise floor of the detector may degrade as power increases above
+15 dBm. Noise in the region of the detector is best measured with about
+10 dBm of drive level. The noise floor is best measured with about
+20 dBm of drive level. This level can be deleted once the original spur is
detected. In a dual channel configuration, the internal noise floor can be
reduced by cross-correlation and can thus make these power
considerations less critical.
— An amplifier (amplifiers if dual channel) must be used in cases where the
signal level out of the DUT is too small to drive the AM detector or is
inadequate to produce a low enough measurement noise floor. In this case
the amplifier should have the following characteristics.
— It should have the lowest possible noise figure, and the greatest
possible dynamic range.
— It should have only enough gain to get the required signal levels.
Excess gain leads to amplifiers operating in gain compression,
increasing their likelihood of suppressing the AM noise to be
measured.
— The amplifier’s sensitivity to power supply noise and the supply noise
itself must both be minimized.
The following general guidelines should be considered when setting up and making an AM-noise
measurement.