Jackson Labs PHASE STATION 53100A, User Manual

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PhaseStation 53100A User’s Manual V1.04 25-Apr-2022 50
Ground loops are a more likely offender, since all ports on the 53100A have ground pins
or shields that are bonded to the instrument’s metal enclosure. If you can identify the
offending loop, you may be able to break its RF path with a coaxial balun
9
.
You can also attack the source of the loop by bonding all equipment to a common
ground that’s connected to the building’s power distribution network in only one place.
To do this, ensure that all devices participating in the measurement – DUT, reference,
instrument, computer, and everything connected to them – are all part of the same AC
circuit, preferably a power strip that allows all equipment to be plugged into a single
outlet.
Using battery power can help, but batteries shouldn’t be your first resort. Less drastic
solutions can usually be found that will let you use the available AC power. (Try
switching to MDEV, for instance.) If you are measuring stable sources with sufficient
warmup time, you can attenuate line spurs by selecting the 5 Hz
Measurement BW
option in the acquisition dialog. As another alternative, consider the Edit →Apply notch
filter to phase data ( n ) command, described on page 89.
Other environmental hazards
Above, a measurement of two 10 MHz sources was interrupted by bursts of apparently-
random noise at roughly 50-second intervals. The culprit turned out to be a cellular
phone sitting on a nearby bench. In another instance, a breadboarded RF amplifier
9
E.g., http://www.minicircuits.com/pdfs/FTB-1-1+.pdf
.
When using coaxial baluns, make sure they’re actually helping, though. In particular,
watch out for elevated phase noise floors, crosstalk artifacts, and assorted spurious responses picked up by the now-ungrounded coax shield.
Coaxial baluns turn loop antennas into dipole antennas.
Figure 15: Interference from nearby cellular telephone