[time-nuts] Measure GPSDO stability with minimum resources?
bob at evoria.net
Thu Oct 6 13:32:01 EDT 2016
said: "The somewhat amazing holdover estimates on the HP units are one example of this problem. It does not take much testing to quickly realize that they are far more often wrong than right on a unit that has been on power for less than a few weeks."
Thank you Bob. These two sentences clear it all up. Silly me thinking that the HP units could actually project aging from minimum data. I can sample every hour and always have the past 24 hours to look at. In fact, it might even be better to have multiple days in the queue and take a simple average for projection. Naivety has been my biggest foe in this project.
GFS GPSDO list:
From: Bob Camp <kb8tq at n1k.org>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Thursday, October 6, 2016 12:24 PM
Subject: Re: [time-nuts] Measure GPSDO stability with minimum resources?
As normally used, the term “aging” means the long term drift in the frequency of an OCXO.
It is independent of the temperature effects and things like retrace, warmup, and voltage
stability. It is rare that there is any impact on the aging of a properly designed OCXO from
drift of the oven temperature.
Any time you try to estimate (or measure) aging on an OCXO, you will have a hard time
separating it from the other things that affect the frequency of the oscillator. The somewhat
amazing holdover estimates on the HP units are one example of this problem. It does not
take much testing to quickly realize that they are far more often wrong than right on a unit
that has been on power for less than a few weeks.
> On Oct 6, 2016, at 1:11 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> Wouldn't "aging" be the change in the temperature v. frequncy graph over
> time? It is hard to hold temperture constant so maybe record the
> function at several different times.
> This is one big advantage of using a microprocessor inside the GPSDO, It
> can log internal data to either a SD card or use a USB link to a PC to be
> recored in log files. Even my "simple as possible" GPSDO push data to a
> PC over USB. It is easy to glue a temperature sensor to "whatever" and
> log it
> On Wed, Oct 5, 2016 at 10:14 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>> j99harman at gmail.com said:
>>> Unless the oscillator is still warming up, 5 minutes or even 60 is way
>>> short a time to look at aging. For aging, you will want to look at the
>>> change in DAC values over several days at least.
>> I think it's worse than that. You have to hold the temperature constant,
>> maybe even the power supply voltage. A probe on the crystal can might
>> you to correct for temperature.
>> These are my opinions. I hate spam.
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> Chris Albertson
> Redondo Beach, California
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