Bob Camp lists at rtty.us
Wed Feb 27 15:11:53 EST 2013

```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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you are not the intended recipient, you may not read, copy, distribute, or
use this information. If you have received this transmission in error,
please notify the sender immediately by reply e-mail and then delete this
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