Agilent Technologies E1420B, Руководство пользователя

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Residual Measurement Fundamentals
7
Agilent E5505A User’s Guide 207
Calibration and measurement guidelines
The following general guidelines should be considered when setting up and
making a residual two-port phase noise measurement.
1 For residual phase noise measurements, the source noise must be
correlated.
a
The phase delay difference in the paths between the power splitter and
the phase detector must be kept to a minimum when making residual
noise measurements. In other words, by keeping the cables between the
phase detector and power splitter short,
τ
will be small. The attenuation
of the source noise is a function of the carrier offset frequency, and the
delay time
(
τ
)
and is equal to:
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
, source noise is
rejected completely. the first null in noise can be used to determine the
delay difference. At
, source noise shows up unattenuated. At
lower offsets, source noise is attenuated at 20 dB per decade rate at 0.1
of
, source noise is attenuated 20 dB. Examples of sources which best
meet these requirements are the 8644B and 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
Φ
M
conversion in the DUT
.
Mixer-type phase detectors only provide about 20 to 30 dB of rejection to AM
noise in a
Φ
M
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
f
1
τ
---
=
f
1
2
π
τ
----------
=
1
2
π
τ
----------