[time-nuts] DOCXO vs. Rubidium medium-term stability
Bob Camp
lists at rtty.us
Sat Nov 20 03:06:11 UTC 2010
Hi
If high temperature is an issue, keeping the Rb cool will be a major chore. The OCXO will be far more "happy" at 75 than the Rb will be at 65.
Depending on just how mobile we're talking about, the OCXO may have some issues with 2G tip / acceleration.
There's a lot to consider in a setup like this and without a bit more data we're going to head off into crazy land pretty fast.
Bob
On Nov 19, 2010, at 9:36 PM, SAIDJACK at aol.com wrote:
> 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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