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The attenuation of the source noise is a function of the carrier offset
frequency, and the delay time
b. The source should also have a good broadband phase noise floor
because at sufficiently large carrier offsets it will tend to decorrelate
when measuring components with large delays. At
noise is rejected completely. the first null in noise can be used to
determine the delay difference. At
up unattenuated. At lower offsets, source noise is attenuated at
20 dB per decade rate at.1 of
Examples of sources which best meet these requirements are the
Agilent/HP 8644B and Agilent/HP 8642A/B.
The source used for making residual phase noise measurements must be low
in AM noise because source AM noise can cause AM to
the UUT
.
Mixer-type phase detectors only provide about 20 to 30 dB of rejection to
ΦM
AM noise in a
noise measurement so the AM noise can appear in the
phase noise plot
.
2. It is very important that all components in the test setup be well shielded
from RFI. Unwanted RF coupling between components will make a
measurement setup very vulnerable to external electric fields around it.
The result may well be a setup going out of quadrature simply by people
moving around in the test setup area and altering surrounding electric
fields. A loss of quadrature stops the measurement.
3. When making low-level measurements, the best results will be obtained
from uncluttered setups. Soft foam rubber is very useful for isolating the
UUT and other phase-sensitive components from mechanically-induced
phase noise. The mechanical shock of bumping the test set or kicking
the table will often knock a sensitive residual phase noise measurement
out of quadrature.
Agilent Technologies E5500 Phase Noise Measurement System 8-7
Residual Measurement Fundamentals
Calibrating the Measurement
and is equal to:
(τ )
f
=
1
--------- -
, source noise shows
f
=
π
τ
2
1
--------- -
, source noise is attenuated 20 dB.
π
τ
2
ΦM
conversion in
1
-- -
, source
τ
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