Fm Bandwidth - Agilent Technologies 83620A Service Manual

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20. FM Bandwidth

Description and Procedure
Use this procedure to verify that the RF output power does not vary more
than a speci ed amount over the speci ed frequency modulation rate frequency
range. A low frequency spectrum analyzer with a tracking generator operates
as a network analyzer to measure the FM atness. Flatness errors associated
with the tracking generator and spectrum analyzer are calibrated out of
the measurement. Flatness errors due to the power splitter and microwave
ampli er are minimized by external leveling at the ampli er. he delay line
discriminator is used to demodulate the FM from the RF carrier. It also
provides an input to the spectrum analyzer that is equivalent to the tracking
generator frequency and proportional in power to the synthesizer RF output.
he delay line discriminator is formed by driving a mixer with a modulated
carrier into the LO port, and a delayed carrier into the RF port. he delay is
produced with a cable of approximately 3 feet in length. With this setup, the
mixer responds to phase di erences between the two inputs. he cable has a
constant time delay and, as the carrier frequency is frequency-modulated, a
linear phase shift occurs between the mixer inputs. Since the mixer inputs are
in quadrature, the mixer operates as a phase detector that amplitude tracks the
RF input (synthesizer power) and has an output frequency corresponding to
the FM rate (tracking generator frequency).
2-118 Performance Tests HP 8360
FM Bandwidth