Garren Davis garren.davis at qlogic.com
Wed Feb 27 17:43:24 EST 2013

```Opps, Now your confusing me. You say the tbolt does not use the temperature monitor when in locked mode. In your previous message you said "The temperature of your TBolt is moving 2.5 C. The OCXO frequency directly follows this temperature". Do you mean the inner oven is changing .008C because of the 2.5C change in the outer oven?
I'll back away from all the questions for a while and study this a bit. Probably move some thermistors to different locations.

It is fun trying different things and seeing what happens.

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.

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"

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
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

888888888888888888888

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