[time-nuts] DOCXO vs. Rubidium medium-term stability
SAIDJACK at aol.com
SAIDJACK at aol.com
Sat Nov 20 02:36:11 UTC 2010
Hi Dave,
forgot to mention:
The PRS-10 also has a limited temperature range only up to +65C, so
military applications are a no-go. A good DOCXO will have +75C or even +85C
capability.
Also, the spec for the PRS-10 is 1.18E-012 per Degree C temperature change,
and the units I mentioned before with the DOCXO are available in better
than 2E-012 per Degree C over a wider temp range, so are very similar in
performance over temperature.
bye,
Said
In a message dated 11/19/2010 18:12:13 Pacific Standard Time,
SAIDJACK at aol.com writes:
Hello Dave,
as some folks have already mentioned here, the best solution for you will
depend on your specific requirements in terms of how much warmup time you
have before GPS is gone, and how much drift your solution can handle.
The PRS-10 is a good unit, but requires cooling, a large amount of power,
only has a single 10MHz and 1PPS output, and it has a somewhat noisy
output in terms of phase noise and short-term-stability. It also costs
about
$1500, is quite large, and does not provide a GPS receiver, nor one
especially
optimized for timing.
You may want to look at the Fury or FireFly-IIA GPSDO units, these are
lower cost, include the complete GPS sub-system, achieve performance
similar to
the PRS-10 after sufficient warmup, are much smaller, lower power, the
FireFly-IIA has a built-in isolated distribution amplifier, and don't have
an
Rb lamp life limitation. Typical Fury DOCXO units can achieve better than
1us drift over 24 hours after they have fully stabilized, which is better
than many Rubidium references.
If you are looking for drift in the <10us range per day, you will need a
double oven SC-cut OCXO.
You didn't mention if your application was airborne, in that case you may
need a low-g sensitivity oscillator to avoid loss of short term stability
and increased phase noise due to aircraft vibration and acceleration.
Rubidiums are especially sensitive to airborne vibration such as caused
by
Turboprops, Rotorcraft, etc.
Without having your specifications for the warmup time, thermal changes,
and the desired drift, it is difficult to say if a single oven, double
oven,
Cesium, or Rubidium based unit would work for you.
Lastly, unless you are underwater or under-ground, GPS should be
available
with a modern, good jamming-resistant receiver, and if it is a modern
GPSDO will perform as well or better than a modern Rb.
bye,
Said
In a message dated 11/19/2010 14:43:43 Pacific Standard Time,
lists at rtty.us
writes:
>
> 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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