[time-nuts] Lady Heather numbers

Garren Davis garren.davis at qlogic.com
Tue Mar 5 21:38:58 UTC 2013


Thanks Bob,

My first run I had an 80mV and 2.5C swing and after some improvements I have a 23mV and 1C swing. So
I was able to make things better but clearly I have a ways to go.

The 136 second holdover was because I opened the oven to make some changes but didn't reset Lady
Heather for a clean run. That was two days before I did a screen capture so everything should have
stabilized.

Can anyone tell me how to turn off the satellite display on the lower right of the display?

Garren


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
Sent: Tuesday, March 05, 2013 9:01 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Lady Heather numbers

Hi

Your dac voltage is still swinging 20 to 25 mV over the period (4 to 5 divisions at 5,000 uV per division). It tracks the temperature as reported by the sensor just about 1:1 (yellow and green lines follow each other). It still looks like your OCXO is moving around quite a bit with temperature.

At 3 Hz/volt (best guess on your OCXO) you are moving 0.06 to 0.075 Hz at 10 MHz. That's about 6 to 7.5 ppb for a reported ~ 1 C change (4 to 5 divisions at 0.2 C per division). Since the two track well, it's a good bet that at least 90% of what you are seeing it temperature.

One very easy way to see the impact of the OCXO moving around - the yellow
"Holdover: 136 secs" message. For a properly operating unit the dimensions should be hours, not ~ 2 minutes.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Garren Davis
Sent: Tuesday, March 05, 2013 11:04 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lady Heather numbers



I think I have my temperature problem fixed. I have included a 24 hour graph. Comments welcomed.
I also did a 48 hour survey. I have more things I'm going to change but wanted to do one thing at a time. I have a new GPS antenna on the roof but it is not connected yet.
I also want to try
a different power supply.

Garren


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
Sent: Wednesday, February 27, 2013 12:12 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Lady Heather numbers

Hi

The TBolt does not use the temperature monitor when in locked mode. Your OCXO is changing temperature. Roughly a 0.008 C temperature change would explain the movement you see.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Garren Davis
Sent: Wednesday, February 27, 2013 1:20 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lady Heather numbers


I don't doubt that my oven could be the problem but I would think a lot of people have their tbolts sitting in a room or basement with a lot more temperature swing than 2.5C. I also monitor the inner oven temperature where the oscillator is located and it remains stable at 67C regardless of the 2.5C swing of the outer oven. This makes me wonder if the tbolt temperature is used in the algorithm that steers the osc frequency. I'll have to try some experiments to see if I can figure this out.

Thanks for the feedback Bob.

Garren


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
Sent: Wednesday, February 27, 2013 9:49 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Lady Heather numbers

Hi

The temperature of your TBolt is moving 2.5 C. The OCXO frequency directly follows this temperature. The OCXO is likely moving 3 ppb as the temperature changes by 2.5C. That drives the PPS back and forth.

Put another way - most of what you see is related to the problem with the OCXO and it's lack of a proper oven.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Garren Davis
Sent: Wednesday, February 27, 2013 10:27 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lady Heather numbers


Warren,

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.

Garren


-----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".

ws

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

Hi,

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.
Thanks.
Garren

**************************
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.

Garren




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