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RF phase noise measurement using spectrum analyzer

This page describes RF phase noise measurement using spectrum analyzer. It mentions RF phase noise measurement basics with phase noise test setup using spectrum analyzer.

As we know phase noise is the measurement which helps in verifying the purity of the RF signal under test. It is measured for various RF components, devices and systems which include crystal oscillator, Local Oscillator, Synthesizer, Up/Down Frequency converters etc.
Refer RF phase noise and phase jitter basics and conversion➤.

Phase Noise is specified as follows:
"Phase Noise is equal to -60dBc/Hz at 1KHz" for say RF synthesizer output of say 6 GHz.

Test setup for RF phase noise measurement using spectrum analyzer

RF phase noise test setup
Figure-1: RF phase noise test setup using spectrum analyzer

The best method to measure phase noise with the use of RF spectrum analyzer. The figure-1 depicts typical setup used for RF phase noise measurement. As shown in the figure, RF output of DUT (Device Under Test) say RF synthesizer is connected with RF INPUT of Spectrum Analyzer.

Following settings need to be done in the spectrum analyzer to measure phase noise with optimum accuracy for the above specification.
➨Center Frequency(Fc) = 6 GHz
➨Span = 10 KHz
➨ Marker (δ) = 1KHz
➨RBW (Resolution Bandwidth) = 100 Hz
➨VBW (Video Bandwidth) = 1 KHz (Check the display and set accordingly to obtain desired result).

RF phase noise measurements
Figure-2: RF phase noise measurement

As shown in the figure, RBW has great effect on RF phase noise measurement using Spectrum Analyzer. Hence the optimum RBW is selected for the best measurement corresponding to RF output and span.

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