Reading the recent discussion about GPS receivers for a Stratum 1 NTP server caused me to reflect on the Symmetricom TimeSource 2500 I have been using for years as a GPS-based frequency reference. I only turn this on for a couple of days when it is likely I will need it, but am not sure if this intermittent operation really achieves stratum 1 performance. A disappointment of the 2500's architecture is that it burns an SRI PRS-10 in the background as a backup in case of the loss of GPS. This seems wasteful to me as the operating life of the PRS-10 units is not unlimited. I suppose the PRS-10 could be disabled, but this would require some simulation circuitry as the 2500 monitors the PRS-10 and goes into a fault condition if the expected PRS-10 presence is absent. Certainly others have utilized these units for such use. Has anyone performed a detailed evaluation of the 2500 units in intermittent service? Bruce hunter, KG6OJI

		Attila Kinali

On Mon, 22 Jan 2018 13:17:40 -0500 Bruce Hunter via time-nuts <time-nuts@febo.com> wrote: > A disappointment of the 2500's architecture is that it burns an SRI PRS-10 in > the background as a backup in case of the loss of GPS. This seems wasteful > to me as the operating life of the PRS-10 units is not unlimited. I suppose > the PRS-10 could be disabled, but this would require some simulation > circuitry as the 2500 monitors the PRS-10 and goes into a fault condition if > the expected PRS-10 presence is absent. Certainly others have utilized these > units for such use. Has anyone performed a detailed evaluation of the 2500 > units in intermittent service? The PRS-10 is in there because someone needed the additional stability performance. And to achieve that you need to run it continuously, because you need to measure its frequency and correct it as it slowly drifts. As with crystal oscillators, Rb have a retrace as well, so just measuring the frequency and shutting it off, will not do. So, what you want is bascially switching off the main component of the system. Besides, switching an Rb on and off is not a good thing for its lifespan. It's like a incandescent light bulb: They can run for decades if continuously under power, but if you switch them on and off once a day, they die within a few months. Also, Rb are spec'ed for a lifespan in the order of 20 years (the PRS10 has a lifespan of 27 years). Nobody complains if a piece of equipment needs to be replaced/repaired every 20 to 30 years. Most likely the power supply will die well before you get even to the Rb failing. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson