[Milsurplus] Fwd: US Navy Returning To CW Training

[Francesco Ledda]

Actually, it is a little different.

When the GPS clock is lost, the oscillator enters a mode called Holdover.
In this mode, the clock is held at the last good frequency.  It will remain
in this mode, until the GPS clock returns.  The local oscillator has a
prescribed frequency short and long term stability.  The network will work
properly with a complete GPS outage. The synchronizes and desynchronize can
operate properly with some frequency offset. This kind of technology was
created in the late 80s (SONET).

F

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
Hubert Miller
Sent: Tuesday, February 09, 2016 1:40 PM
To: Milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Fwd: US Navy Returning To CW Training


  The telco office i recently retired from has two GPS systems for 
supplying office timing, primary and secondary.
I was told that if both GPS fail, the oscillator in the clock 
distributor will run in free mode, undisciplined mode,
or whatever it's called, for at least two weeks with reliable timing. 
The clock distributor is in a 19 inch rack  by
about 6 inches tall, but most of the card slots in it are distributor 
cards, and the oscillator is only one or two
slots, so that technology would fit in a cellphone site, i would think.
The first GPS installed, maybe 15 years ago, was a big deal, antenna on 
the building roof, coax, waterproofing
entries and lightning protection. We had problems twice, once with 
electrical failure and once with water entry.
In those days, if i recall, timing was derived from a channel on an 
optical circuit. The most recent GPS made me
think of something you could buy off Amazon or Walmart even. After the 
tech found a good window location,
he glued the small plastic thing to the inside of the window, then the 
rest of the coax was run inside the building.
No more weather problems.
-Hue Miller
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