3.2.2 Water Condensation and Excessive Humidity
Water condensation and excessive humidity condensation of moisture on the electrical components
produce frequency spikes or instability until the heat of the operating unit drives out the water vapor.
Condensation does not cause a problem for environments meeting the SA.22c specification, that is, the
SA.22c base plate thermal ramp rates are controlled so that they rise at less than 2 °C/minute.
3.2.3 Excessive Dust
Operating the unit in dusty conditions cause unexpected thermal effects, if dust builds up on the top
surface. Excessive dust contributes to contamination in the shell of the mating connector and causes
intermittent loss of signals.
The SA.22c 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.
3.3 External Interfaces and Grounding
SA.22c Dimensions (see page 4) shows the interface circuitry for the 18-pin SAMTEC I/O connector
and the mechanical dimensions of the SA.22c. 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 to the mating connector for the operation of the SA.22c unit.
The SA.22c is constructed with the chassis (unit cover) and signal grounds tied together at multiple
points. The power supply return is isolated from both chassis and signal grounds by a ferrite bead. This
robust grounding approach offers ESD protection and low spurious emissions, however, it may lead to
ground loop issues.
Workarounds commonly used to break DC ground loops at a higher level of integration are:
Using an RF isolation transformer for the sine RF output
Floating the transformer secondary winding of the user’s power supply
3.4 Electrical Interface
The following sections provide information regarding the main input/output signals of the SA22c.
3.4.1 1PPS Input and Output
The 1PPS output signal of the SA.22c unit is positive-edge triggered and gated with the rising edge of the
clock. Its duration for a 10 MHz unit is 400 ns ±10% and the rise/fall time is 4 ns.
3.4.2 Lock Signal
The lock signal indicates that the internal voltage controlled crystal oscillator (VCXO) is locked to the
atomic transition. If the lock signal is low after the warm-up is complete, the output frequency is locked
to the rubidium atomic clock.
If the lock signal is high, the atomic lock is lost and the SA.22c goes into sweep mode to reacquire lock.
The sweep ranges from approximately –21 ppm to 21 ppm in a 20-second period approximately. During
the sweep, outputs are maintained but signal accuracy should not be relied upon during sweeping. If the
power source to the SA.22c is off, the lock output line is low.
3.4.3 Service Signal
The service signal is valid when the unit is operating and the rubidium oscillator is locked.
The service signal algorithm monitors the health of the rubidium physics package, which includes the Rb
lamp bulb and resonator cell and the unit’s crystal oscillator that is slaved to the rubidium atomic clock.
The service signal indicates low approximately one month before any of the internal operating
parameters are near the end of their tuning or adjustment range.
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