[time-nuts] Lady Heather numbers

Garren Davis garren.davis at qlogic.com
Wed Feb 27 10:27:12 EST 2013


Thanks for the comments. I've included a 34 hour screen dump. Trying to understand why
the PPS trace is doing what it is doing. Looks like it might have something to do with
the temperature.

I'm going to try a different GPS antenna and mount it higher this weekend. I'll do a 24 hour
survey and start another run. After that I'll try a different power supply. Right now I'm
using a PC power supply. It's probably a bit noisy.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of WarrenS
Sent: Tuesday, February 26, 2013 10:53 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lady Heather numbers

>Can anyone comment on the picture.
>I don't know if what I have would be considered good as far as accuracy
>and stability is concerned.

The screen dump is way too short to give much detail.
What can be said from what is there:
>From a Ham standpoint it is all working fine and is much better than 1e-9.

>From a time nut standpoint it is very poor.
It is using the default setting (for the most part) Phase error at -100ns is ~50 times high for the 100 sec TC setting used, (likely due to the high drift rate of the Osc) Frequency error is wondering around 1e-10 is about 50 times higher than what is possible.
Effect on freq and phase noise with sat changes is >>10 times more that what is possible with good setup.

Concerning your Dac comments, Yes makes sense, but your conclusing is wrong.
Can't say or sure, because the 24 Hr + screen shot is not shown, but in general The Tbolt temperature reading has no direct effect on the Dac control voltage unless the Tbolt is in hold over.
The Dac voltage changes because the oscillator's freq is trying to change, not the other way around.
You can disable the Dac from changing with "dd".


From: "Garren Davis"
Subject: [time-nuts] Lady Heather numbers


I have been playing with my thunderbolt and Lady Heather over the weekend. I
hope it's ok
that I attached a screen dump of what I have. Can anyone comment on the
picture. It's been
running less than a day and I don't know if what I have would be considered
good as far as
accuracy and stability is concerned.

Garren Davis garren.davis at qlogic.com

>From looking at the graph over 24 hours it looks like the outer oven varies
>about +-.5C. This is
from the tbolt temperature sensor as the tbolt is in the outer oven. The
inner oven where the
oscillator is located holds at 66.4C. My concern is that it looks like the
tbolt algorithm controls
the DAC voltage depending on the temperature that the tbolt reads.
Temperature goes up, the DAC
voltage goes up. If the inner oven is holding steady then I don't want the
DAC voltage changing
if the temperature in the outer oven is changing. Is there any way to tell
the tbolt algorithm to
ignore the temperature in its DAC calculation?

Wow, I hope this makes sense the way I explained it.



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