Spectracom SecureSync User Reference Manual page 214

3.6 OTHER Setup Pages
INTERFACES/OUTPUTS, or
INTERFACES/OPTION CARDS
and select the 1PPS Output or 10 MHz Output you would like to see, or configure.
The 10 MHz signal is provided by the internal oscillator. External 1PPS sources ("references")—if
present and valid—are utilized to discipline the oscillator, in other words to correct for oscillator drift
(the oscillator cannot discipline to either NTP input, or a User set time). If no external 1PPS input
references that can be used for disciplining 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 fall-
ing 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 reference, 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 unavailable) and even after input ref-
erences 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 reference
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 ref-
erence 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 reference is
lost. See also "Signature Control" on page 201.
198 CHAPTER •
3 SecureSync User Reference Guide Rev. 18