Thanks awallin
The software documentation states that the Allan Deviation is calculated by comparing:
The software documentation states that the Allan Deviation is calculated by comparing the:
1pps signal locally generated from the OCXO by means of a frequency divider
With
The receiver’s 1pps (derived from the satellite constellation).
However, when I read (again) further it appears to answer my question.
“The comparison of these two PPS signals is the input information to the unit’s frequency standard
control loop. Because this input information is dominated by the GPS 1pps jitter (resulting largely
from GPS receiver and propagation limitations),
do not be fooled into thinking that the Time Stability
Measure presented here is that of your frequency standard. It is only an internal value which
indicates overall system performance (including the GPS reception). For reliable stability
measurements, you should make independent measurements against a local high stability reference.
The task of the frequency standard’s control loop is to ‘marry’ the high short-term stability of the
internal OCXO with the high long-term time stability of the GPS system. For this reason the 10MHz
output of your unit will have significantly better stability (for short observation times) than the
values indicated in the Time Stability Measures chart.”
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