Hi Bob,
But will any of the things you mentioned show up as a more or less linear march
downhill at about 1 step per hour over the course of 7 days? In fact, I think
Dan's units show about the same -1 per hour, and he's had them running
continuously for many months. I believe you use these same OCXOs, Bob.
They're Trimble 34310-T units salvaged from China. What's been your experience
with them over the long run as far as aging is concerned?
Bob
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AE6RV.com
GFS GPSDO list:
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From: Bob Camp <[email protected]>
To: Discussion of precise time and frequency measurement <[email protected]>
Sent: Saturday, November 5, 2016 7:37 PM
Subject: Re: [time-nuts] Thermal impact on OCXO
Hi
2^20 is roughly 1 ppm. It is about 5 uV on a 5V line or 2.5 uV on a 2.5 V EFC
center.
A DAC that does 100 ppm / C is a pretty typical part. 10 ppm / C is
unusually good
A “good” voltage reference might do 2 ppm / C
A very typical room will swing around +/- 2C without much going on.
Open the door in the room or open a window and 10C is not unusual.
Grabbing a normal banana plug with your fingers will give you > 10 uV,
other thermocouples are running around
A DAC with < 10 uV of noise in the 0.01 to 1 Hz region is unusually good
That’s just looking at the easy to measure part of the system. A few hundred uV
delta on
the PCB between the OCXO ground pin and “ground” from grabbing the OCXO is
harder
to measure, but also pretty typical. It sums right into the EFC line.
It’s not a rabbit hole so much as the details of the design at the level you
have chosen
to look at.
Bob
> On Nov 5, 2016, at 8:10 PM, Bob Stewart <[email protected]> wrote:
>
> This seems to be turning into a rabbit hole from which there can be no
> possible return. With no evidence, you question my competence and cast
> aspersions on my testing methodology. I give up.
>
> Have a nice day.
>
> Bob -----------------------------------------------------------------
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
> From: Azelio Boriani <[email protected]>
> To: Discussion of precise time and frequency measurement <[email protected]>
> Sent: Saturday, November 5, 2016 7:02 PM
> Subject: Re: [time-nuts] Thermal impact on OCXO
>
> ...with a 20bit DAC, a suitable voltage reference for that DAC and an
> HP3458...
>
> On Sun, Nov 6, 2016 at 12:39 AM, Bob Stewart <[email protected]> wrote:
>> Hi Hal,
>>
>> With a 20 bit DAC, even a small aging rate is going to show up. I'll let
>> the one GPSDO cook for a month or so and see what it shows then. I'll also
>> pull the data from the log file and see if I can see any correlation between
>> the temperature and the EFC over time. IOW, for data points separated by
>> 3.5 days, does the temperature difference between the two point seem to play
>> a large part of the change in the recorded DAC value.
>>
>> The graph was made from the logging data sent to the PC. But, the firmware
>> doesn't have access to historical data on the PC, so something is needed for
>> aging calculations. Tom mentioned here recently about the 58503A GPSDO
>> saving 64 hours of data for it's aging calculations. So, I just added a few
>> hours to that to get to 3.5 days of history in the GPSDO.
>> Bob -----------------------------------------------------------------
>> AE6RV.com
>>
>> GFS GPSDO list:
>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>>
>> From: Hal Murray <[email protected]>
>> To: Bob Stewart <[email protected]>
>> Cc: Hal Murray <[email protected]>
>> Sent: Saturday, November 5, 2016 6:23 PM
>> Subject: Re: [time-nuts] Thermal impact on OCXO
>>
>>> The OCXO has been hot for a number of months.
>>
>> Then I don't understand why it is still aging that much.
>>
>>
>>> I changed the firmware to save the DAC voltage every 30 minutes for 3.5
>>> day
>>
>> That's not very long.
>>
>> How did you make the graph? You had to get the data out to a place where you
>> can plot it somehow. If you can do that, why are you "saving" the data? I
>> assume you have a serial port to a PC or something like that.
>>
>>
>>> The fuzz in the temperature line is, indeed, the HVAC cycling
>>
>> You could try putting a box over the unit to see if that slows down the
>> temperature changes.
>>
>> Mostly, you are trying to block air flow.
>>
>>
>>
>> --
>> These are my opinions. I hate spam.
>>
>>
>>
>>
>>
>>
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