[time-nuts] DOCXO vs. Rubidium medium-term stability

[Dave Jabson]

Greetings,

I just discovered this mailing list, this is my first submission. Glad to
find a group of folks who are into this kind of stuff!

I'm working on an data acquisition application for my company that will
require a very stable oscillator. Without going into too many specifics,
there will be some reference stations spaced 100's of kilometers apart from
each other and 1 mobile station that will be operated in an area where GPS
is not available. I need to be able to collect data at all the stations and
have the time synchronization be extremely good between the stations,
including the one without GPS.

For the reference stations it will be sufficient to have the timing of each
one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA
string and 1pps edge and all of the digital electronics will use the GPSDO
10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be
done as needed.

The mobile station can be synchronized to GPS initially to synchronize its
clock as described above but will then have to rely on a free-running
oscillator. The stability of this oscillator will dictate how much drift the
mobile station's clock will experience relative to the reference stations.
Keeping this drift as low as possible is my goal.

I had assumed that a Rubidium oscillator would give me the best stability
over the course of 8-12 hours. Obviously a Cesium would be better but those
are impractical due to cost and power constraints. I've begun evaluation of
a Rb oscillator but now I'm being told by some people that a good DOCXO is
likely to give me similar medium term stability (with obviously better
short-term stability).

Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for
cost and power reasons if there's no performance benefit to be had using a
Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm)
seems to perform well but I am interested in hearing others' thoughts.

Thanks,

Dave

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Dave Jabson
Systems Engineering Manager
Quasar Federal Systems
5754 Pacific Center Blvd, Suite 203
San Diego, CA 92121
858-412-1706
www.quasarfs.com