097-10603-01 Rev. A – November 2004 X72 Desiger’s Reference and User’s Guide 35
Design Integration Considerations
External Interfaces and Grounding
As the base plate temperature continues to increase the unit eventually loses lock.
Above a base plate temperature of +85° C the resonator or lamp heaters shut down
as control point temperatures are exceeded and the unit temperature coefficients
increase to approximately 6xE
–10°
C.
Water Condensation and Excessive Humidity
Condensation of moisture from the air onto electrical components produces
frequency spikes or instability until the heat of the operating unit drives out the water
vapor.
Condensation will not cause a problem for environments meeting the X72
specification if the X72 base plate thermal ramp rates are controlled so that they rise
at less than 2° C/minute.
Excessive Dust
Operating the unit in dusty conditions may cause unexpected thermal effects if dust
builds up on the top surface. Excessive dust will also contribute to contamination in
the shell of the mating connector and could cause intermittent loss of signals.
The X72 is shipped in a dust-protected ESD resistant bag. All connectors on any
product must be suitably protected, before mating, in a dust-controlled environment.
External Interfaces and Grounding
Figure 2-1 shows the interface circuitry for J1, the X72 I/O connector. All signals,
including power, power return, rf output, signal/chassis ground, and monitor lines
are routed through this connector. All voltage supply and ground lines must be
connected at the mating connector for the X72 unit to operate properly.
The X72 is constructed with the chassis (unit cover) and signal grounds tied
together at multiple points, and with the power supply return isolated from both
chassis and signal grounds only by a ferrite bead. This robust grounding approach
allows for ESD protection and low spurious emissions. But it can also lead to ground
loop issues for the user.
Workarounds commonly used to break dc ground loops at a higher level of
integration are to use an rf isolation transformer for the sine rf output, and/or float
the transformer secondary winding of the user's power supply.
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