[time-nuts] RE: phase locking Rb to GPS

Richard H McCorkle mccorkle at ptialaska.net
Sun Oct 23 14:14:22 EDT 2005

     While I have not used an Isotemp OCXO134-12 specifically, I am
currently running two different OCXO134-10 units in 2 different GPS
receivers. I am currently watching the performance of both units as they age
in because the two oscillators have very different characteristics. The spec
sheet for the 134-10 lists the short-term stability as < 1e-10 / sec, and
both units meet this spec, with long-term aging at <1e-9 after 30 days,
5e-10 after 1 year, with both units also meeting this spec after 30 days.
     The first unit I built had a very steep (~5e-9 / day) initial aging
curve, which has settled to ~1.2e-10 / day after a couple of months of run
time. This unit has good short-term stability, with the EFC varying no more
than +/- 1e-11 over 100 minutes, similar to what you are seeing with a 7
minute period. The long-term aging on this unit while well within spec is
still double the aging of the second unit after months of operation.
      The second OCXO134-10 unit had extremely low initial aging and has
remained at ~6e-11 / day over the last couple of months. While the aging is
excellent, the short-term stability of this unit is poor compared to the
first unit, with the EFC varying about +/- 1e-10 over 100 minutes. The
variations in EFC on both of my units appear to be cyclic with about a
100-minute period. Since both units are the same model, but with different
P/N and both meet the OCXO134-10 spec but have different characteristics I
believe they were each optimized for a different characteristic when
originally ordered, one for low aging, and one for high stability.
     Not knowing what the particular specs for the OCXO134-12 are, perhaps
they used a faster response time in that unit compared to my 2 OCXO134-10
units and what you are seeing at a 7 minute period is what I am seeing at a
100 minute period. I have 2 more OCXO134-10 units coming from an e-bay
auction to see how they compare with the two I have running. If testing the
two new ones against the two I have running reveals anything I will pass it

----- Original Message ----- 
From: "Alberto di Bene" <dibene at usa.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Sunday, October 23, 2005 7:30 AM
Subject: [time-nuts] RE: phase locking Rb to GPS

> Richard H McCorkle wrote:
> > [snip]
> >     In interfacing an Isotemp mil spec version of the HP 10811B with a
> > sensitivity of 9.7e-9/volt and a span of 4.85e-8 to the Shera controller
> > even with  [snip]
> Richard,
>   do you perhaps have any experience of using the Isotemp OCXO134-12 unit
> I built a GPSDO using it, and it works rather well, were it not for a
> residual oscillation of the frequency of about +- 2E-11. i.e. +- 0.0002Hz
> at 10MHz, with an oscillation period of about 7 minutes, which is too fast
> to be corrected by the PI software loop.
> I attributed it, lacking other explanations, to an imperfect temperature
> control of the oven. Translated in temperature terms, that frequency
> oscillation amounts to a change of about 0.18 degrees Celsius.
> What you think about this ?  TNX
> 73  Alberto  I2PHD
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