Spectracom SecureSync 1200 User Reference Manual page 150

2.17 Configuring Outputs
unless in Host Disciplining mode). If no external 1PPS input references that can be used for dis
ciplining are present, the oscillator will be in Freerun mode.
The selected 1PPS input reference (as configured with the Reference Input Priority table) is used
to align SecureSync's on-time point. The on-time point serves to accurately align the outputs,
such as the 1PPS output, to the correct time, based on its reference inputs.
With at least one 1PPS reference input available and considered valid, SecureSync's on-time
point is initially slewed over a short duration to align itself with the 1PPS reference (this process
can take a few minutes, once an input reference has become available).
SecureSync's 1PPS output is generated from the oscillator's 10 MHz output and is aligned to
the on-time point. The on-time point of the 1PPS output can be configured to be either the rising
or falling edge of the 1PPS signal (by default, the rising edge is the on-time point).
There is a fixed phase relationship between the 1PPS and the 10 MHz outputs, as described
below:
SecureSync equipped with TCXO/OCXO/Low-Phase-Noise Rubidium oscillator : With
oscillator disciplining active (one or more 1PPS references available and valid) and
after the on-time point has been initially slewed into alignment with the selected ref
erence, there will always be exactly 10 million counts of the oscillator between each
1PPS output, even while in the Holdover mode (= input references are currently unavail
able) and even after input references have become available again.
SecureSync equipped with Rubidium (Rb) oscillator : With oscillator disciplining active
(one or more 1PPS references available and valid), after the on-time point has been
slewed into alignment with the selected reference, with the exception of 1PPS input ref
erence changes occurring, there will always be exactly 10 million oscillator counts
between each PPS output pulse.
With the Rubidium oscillator installed, when a 1PPS input reference change occurs (such
as switching from IRIG input to GNSS input, or switching from a reference being valid to
no reference being present or valid—known as the Holdover mode), the oscillator counts
between two 1PPS outputs may momentarily not be exactly 10 million counts. Once the
reference transition has occurred, however, the counts between each PPS output pulse
will return to exactly 10 million counts.
Like other types of SecureSync's signal outputs, a 1PPS output can be configured in several
ways:
Signature Control allows you to determine under which conditions an output signal shall
be present, i.e. what SecureSync will do about a given output when an external ref
erence is lost. See also "Signature Control" on page 136.
The on-time point of the 1PPS signal: rising or falling edge
The pulse width
An offset can be entered to account for cable delays or other latencies.
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