[time-nuts] Lady Heather numbers

Bob Camp lists at rtty.us
Tue Mar 12 13:15:05 EDT 2013


Hi

That looks a lot better. Your DAC has moved about 40 mV over the time
period. That's not bad, given what you did to it. The ~ 14 ppb shift should
settle out something much lower in a week or two.

Good numbers on the PPS are in the 2 to 3 ns RMS region. The oscillator
numbers are a best estimate / derived value. It's easier to see what's going
on there by looking at the DAC voltage once things settle. 

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 12, 2013 12:56 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lady Heather numbers


Bob,

Took your advice and ordered another OCXO. While waiting for it I decided to
cut open the
OCXO with a bad heater that came with the thunderbolt. I found the 1 ohm
resistor from the
12 volt pin to the heater circuit popped off its solder pads and was laying
between the
insulation and the metal enclosure. While unsoldering the circuit board to
fix this the
1 ohm resistor in the oscillator circuit popped off its solder pads. For
others that have
OCXO's that don't work this is an easy fix. They are large surface mount
resistors and easy
to solder. Anyways I put the circuit board back in the metal enclosure but
did not seal
it. I put the OCXO back in my double oven and started a run. The enclosed
picture is a 72
hour display. Even though the DAC was still increasing it looked like the
PPS had stabilized
so I did an auto calibrate. You can see this at marker 1. That was almost
two days ago.

Questions:
1. Is it normal to take this long for the PPS to stabilize?
2. Is it normal for the DAC to keep increasing after two days?
3. In general what numbers would be considered good for the PPS and OSC?

Thanks.

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 2:22 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Lady Heather numbers

Hi

Get a new OCXO

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 4:39 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lady Heather numbers


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




888888888888888888888

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