Jackson Labs PHASE STATION 53100A, Руководство пользователя

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PhaseStation 53100A User’s Manual V1.04 25-Apr-2022 28
Working with dual reference sources
The use of dual references carries significant advantages in noise measurement due to the instrument’s
use of cross spectrum averaging to remove the influence of uncorrelated reference sources over time.
Multiple references can be helpful in stability measurement as well, since the 53100A can easily acquire
the multichannel data necessary for so-called “three-cornered hat” processing.
For a detailed “case study” featuring the use of dual reference sources in both stability and noise
measurement roles, please refer to Application Note 53100A-2,
Dual Reference Noise and Stability
Measurements with the PhaseStation™ 53100A
.
The use of dual independent references relaxes some of the constraints on the stability and/or noise
performance of the reference signal sources, but the advantages come with a new requirement:
the
references must be truly independent and uncorrelated . Otherwise, cross-correlated phase noise and
AM noise measurements will not converge at the DUT’s true noise level, and three-cornered hat
measurements will not benefit from the statistical independence required to separate the frequency
variances at the individual channels.
Two OCXOs running from the same power supply, for instance, may not be as independent as they look.
They may even injection-lock to each other through their power supply connections if decoupling isn’t
adequate. When working with dual references, consider enclosing each of them in its own RF-tight box
or other sealed metal container. Use high-quality DC feedthrough capacitors rather than conventional
power jacks or connectors. These precautions are always a good idea, but they’re absolutely mandatory
with OCXOs whose output signals are obtained from discrete pins or SMT pads rather than coaxial
outputs.
53100A instruments equipped with optional dual internal references are particularly easy to set up since
reference channel isolation isn’t a concern. There are no inherent performance differences associated
with the choice of external and internal reference, but the internal reference option offers the practical
advantage of allowing the 53100A to measure high-performance sources with no connections other
than USB, power, and the DUT itself.
Internal and external reference jack configurations are shown in the PhaseStation 53100A Measurement
Roles
section (page 131.) When reviewing the dual-reference measurement role descriptions, note that
the REFERENCE, CH 1 OUT, and CH 2 OUT jacks remain unconnected when dual references are used,
whether internal or external. As with the DUT, CH 3 OUT, and CH 4 OUT connectors on the right side of
the front panel, these jacks correspond to the input and output ports of an internal RF splitter. The
REFERENCE and DUT channel splitters are provided for user convenience, and have no other internal
connections.
Dual-channel references used with the 53100A do not have to operate at the same frequency. That
being said, when working with external dual-channel sources it can sometimes be helpful to either
phase-lock them together with a loop bandwidth well below the narrowest noise offset of interest, or