[time-nuts] Symmetricom TimeSource 2500

brucekareen at aol.com brucekareen at aol.com
Tue Jan 23 12:28:45 EST 2018

For clarification, from reading the Symmetricom manual, the TS-2500 was designed as a reliable Stratum 1, 10 MHz source for communications systems.  In addition to GPS, the unit monitors the internal SRI PRS-10, and other 10 MHz frequency references that are presented to it.  It tracks and compares these with GPS and keeps long-term records of their behavior.  In the event the GPS signal is lost, the TS-2500 generates a 10 MHz output from its internal oscillator, using the PRS-10 and any other monitored reference inputs as references, after first applying weighting factors developed from experience to determine the appropriate frequency offsets.  In other words, the PRS-10 output is not utilized directly, but only as a reference.  An offset is applied, based upon the retained past monitoring data of the PRS-10 frequency versus GPS.

Should the unit suddenly see the GPS departing from its expected frequency, as compared with multiple other references, it might switch to the holdover-mode, after computing the required offsets from past experience.

A key point is that no provision is made to control the frequency of the PRS-10; it is simply monitored and the offset from GPS continually recorded.  In other words, the PRS-10 does not influence the accuracy or noise of the 10 MHz output unless the GPS reference is lost.  

Bruce Hunter, KG6OJI

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