[time-nuts] Re: 20230122: Please help me understand my OCXO

[Andrew Kalman]

Just a follow-up if anyone is interested ... I ran my test for over a
month, and I conclude that the OCXO's drift has settled to around
0.25-0.33ppb/day. Plot attached.

--Andrew

--------------------------------
Andrew E. Kalman, Ph.D.


On Tue, Jan 24, 2023 at 8:05 AM Andrew Kalman <aekalman at gmail.com> wrote:

> Hi Bob.
>
> That helps a lot -- gives me a lot of insight, esp re measurement
> resolution vs time.
>
> (I'm slowly being dragged into long-time duration measurements, and I'm
> not enjoying the associated energy costs :-) ).
>
> --Andrew
>
> --------------------------------
> Andrew E. Kalman, Ph.D.
>
>
> On Tue, Jan 24, 2023 at 6:15 AM Bob Camp <kb8tq at n1k.org> wrote:
>
>> Hi
>>
>> Looking at the data, past day 10 you get into the “unclear” range. Is the
>> data
>> limited by the test resolution? maybe. It temperature an issue? who
>> knows. Is
>> there something else going on …..
>>
>> After a month or so, you can likely draw a box around data with wobbles
>> in it and
>> make a rational guess about the aging rate. Take the diagonal through
>> that box
>> and it’s a pretty reasonable guess at the max rate.
>>
>> Back in the 70’s 1 ppb per day was a pretty good spec on an OCXO. As time
>> went
>> on, things got better and better. Going from AT to SC crystals helped a
>> bit. Mostly,
>> crystal processing just improved in many small steps over many decades.
>>
>> To really know what category the one you have falls into aging wise, you
>> need more
>> data. A month or three of monitoring will give you a better idea. Best
>> guess is it
>> will fall away to the “need that box” level. You simply will be guessing
>> with the current
>> test setup.
>>
>> Hermetic (or reasonably hermetic) OCXO’s tend to do pretty well after
>> storage. They
>> don’t soak up humidity like the open designs do. What you are seeing is
>> not unusual
>> on a part like you have.
>>
>> How good can it get? I’ve seen groups of OCXO’s from back in the 1970’s
>> that stayed
>> well below 1x10^-8 per year. There are TBolt’s with OCXO’s on them that
>> have even
>> less change per year over the 10 to 30 years since they left the factory.
>>
>> Does aging when powered off count? How long has this or that example been
>> on
>> power vs off power? There’s not a lot of way to get that data on most of
>> these parts.
>> One would *guess* that this or that device did spend significant time on
>> power before
>> it got scrapped out.
>>
>> Take the yearly numbers and do the division. You can get a daily rates.
>> 1x10^-8 / 365
>> gets you 3x10^-11/day. I’d suggest that while it’s a valid use of math,
>> the result isn’t
>> really significant for a “per day” estimate.
>>
>> The good news: Your OCXO seems to be running ok and it’s not broken.
>>
>> Bob
>>
>> > On Jan 24, 2023, at 12:53 AM, Andrew Kalman via time-nuts <
>> time-nuts at lists.febo.com> wrote:
>> >
>> > I recently revived an instrument with a non-small OCXO in it, and I'd
>> like
>> > to better understand what I've measured in terms of the OCXO's accuracy
>> and
>> > aging.
>> >
>> > Background & Test setup:
>> >
>> >   - The OCXO is an Isotemp Model OCXO36-44, date code 9552.
>> >   - It originally came from an XL Microwave Model 3060 -- I dunno if
>> it's
>> >   the Option 112, 115 or 120 OCXO.
>> >   - It has just three connections -- 12V, GND and RF output.
>> >   - I moved it into an XL Microwave frequency counter Model 3080 (10Hz
>> to
>> >   8GHz).
>> >   - In 2017 I adjusted the OCXO (using its coarse and fine adjustment
>> >   screws) to an indicated 10,000,000.00MHz using the
>> >   two-traces-on-an-oscilloscope method and a GSPDO.
>> >   - Around 2019 this Model 3080 stopped working (it blew a transistor on
>> >   its power PCB).
>> >   - A few weeks ago I repaired this Model 3080 (a Schottky power
>> rectifier
>> >   had failed, and took out a transistor). I replaced three rectifiers
>> and two
>> >   transistors in the power supply.
>> >   - Once repaired, the Model 3080 started up immediately and the OCXO
>> >   measured 9,999,999.66MHz.
>> >   - My measurement setup is an HP Z3805A GPSDO providing a 10MHz
>> reference
>> >   that feeds into an XL Microwave Model 3120's external 10MHz reference
>> >   input; the Model 3120 is in turn measuring the Model 3080's 10MHz
>> reference
>> >   output. My recorded data is strictly from the Model 3120's display
>> (max
>> >   digits). All of this equipment is just in my lab, temperature swings
>> are
>> >   small. The Model 3xxx frequency counters have no fans.
>> >
>> > I've attached a picture of the OCXO and a plot of its behavior over 17
>> days
>> > of uptime since the day I repaired it.
>> >
>> > My questions:
>> >
>> >   - *Is my measurement setup one that provides reasonably accurate
>> >   measurements of the OCXO's absolute accuracy and aging?*
>> >   - *Is the "warm up behavior"of this OCXO typical for a nearly 30-year
>> >   old OCXO with unknown total uptime?*
>> >   - *Does my test setup allow me to conclude that the OCXO is
>> >   demonstrating roughly 0.5ppb aging from day 11 onwards?*
>> >   - *From this limited amount of data, is this representative of a
>> great /
>> >   good / average / poor OCXO, and why?*
>> >
>> > Thanks for your responses.
>> >
>> > --Andrew
>> >
>> > --------------------------------
>> > Andrew E. Kalman, Ph.D.
>> >
>> <20170512_IsoTemp_OCXO36-44.jpg><20230109_XL_Microwave_3080_OCXO_Aging.pdf>_______________________________________________
>> > time-nuts mailing list -- time-nuts at lists.febo.com
>> > To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>
>>
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