Jackson Labs RSR GNSS Transcoder User Manual page 125

RSR GNSS Transcoder™ User Manual
due to aging is ~88mV per year. The EFC sensitivity of the crystal is about 8Hz per volt, so the
crystal ages at:
8Hz/V * 0.088V/Year = 0.704Hz/Year drift.
At 10MHz:
0.704Hz / 10MHz = 7.04E-08 aging rate per year.
This is the same as 0.2ppb drift due to aging per day.This crystal aging is fully compensated by the
firmware with and without GPS reception of course.
The board temperature is shown in turqoise. We can see it ranges from 0.135607A to 0.178146A.
The OCXO current jumps lower every 24 hours because the unit is sitting next to a window, and the
sun shines onto the OCXO in the evenings, heating it up, and thus making the unit use lower power
during that event.
In Figure 6.9, which is a zoom of Figure 6.8, we can see the phase offset error of the internal OCXO
to the UTC GPS reference. We can see the maximum drift is -77ns to +93ns. The average is (TI
av=-0.03ns). The standard deviation over the 200 hour plot is sd=11ns. This means the average error
of the 10MHz phase of this unit over 200 hours is only +/-11ns rms. Or, in other words the average
jitter (wander) over 200 hours of operation is:
11ns / 200Hrs = 1.528E-014
or in other words the unit performs as well as a high quality Cesium Atomic reference clock over
long periods of time. The unit disciplines its internal 10MHz reference to within less than +/-80ns
peak to peak of UTC at all times, which is less than one complete clock cycle at 10MHz.
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