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

Bob Camp lists at rtty.us
Fri Nov 19 22:41:36 UTC 2010


Hi

How much "warmup" time do you have before you go mobile?

If the mobile unit can be kept hot before it heads out - the DOCXO wins.  If it's a "power up and roll in 10 minutes" sort of thing, then the Rb is the only way to go.

Bob


On Nov 19, 2010, at 3:56 PM, Dave Jabson wrote:

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