Hi Bob,
Could you expound on "so far below a number of issues"?
In any case, your post implies that something else is aging. I'm using an
ADR4533A as my voltage reference. That feeds an AD8638 op-amp driving an
MMBT2222A pass transistor. That pretty much leaves the divider resistors on an
AD8638 in the EFC string. But, aging is aging from my point of view. I guess
I could prove that by hooking the EFC to my 3456A and plotting that over a few
days.
Bob
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From: Bob Camp <[email protected]>
To: Bob Stewart <[email protected]>
Sent: Saturday, November 5, 2016 8:46 PM
Subject: Re: [time-nuts] Thermal impact on OCXO
Hi
My experience is that the aging on these oscillators is so far below a number
of issues
that you will not be able to see it in under a year on a > 10 year old unit.
Bob
> On Nov 5, 2016, at 9:06 PM, Bob Stewart <[email protected]> wrote:
>
> 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
>
> -----------------------------------------------------------------
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
>
> 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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