User`s guide

11-2 Agilent Technologies E5500 Phase Noise Measurement System
FM Discriminator Measurement Examples
Introduction
Introduction
These two measurement examples demostrates the FM Discriminator
measurement technique for measuring the phase noise of a signal source
using two different calibration methods.
These measurement techniques work well for measuring free-running
oscillators that drift over a range that exceeds the tuning range limits of the
phase-locked-loop measurement technique. The Discriminator measurement
is also useful for measuring sources when a VCO reference source is not
available to provide adequate drift tracking.
The setup for a discriminator measurement uses a delay line to convert
frequency fluctuations to phase fluctuations and a phase shifter to set
quadrature at the phase detector.
In the Discriminator measurement, the source is placed ahead of the power
splitter. One output of the splitter feeds a delay line with enough delay to
decorrelate the source noise. The delay line generates a phase shift
proportional to the frequency. The phase shift is measured in the phase
detector by comparing the delay output with the other output from the
splitter. The output of the phase detector is a voltage proportional to the
frequency fluctuations of the source.
For more information about FM Discrimination basics, refer to Chapter 10,
“FM Discriminator Fundamentals”.