[time-nuts] Lady Heather numbers
warrensjmail-one at yahoo.com
Wed Feb 27 13:40:47 EST 2013
The 34 hr plot helps a lot to see what is going on.
First off let me say what you have is working fine for most any real
but if you want to be extreme time nuts, there are lots of improvements that
can be made.
In no special order.
1) Signal level is about 10 dBc lower than ideal, It is not much of an issue
until other things have been improved.
2) The Dac Gain is still at the default of -5.0 Hz /V, Best to 'calibrate"
that. Again not a big deal yet.
3) The Damping is at the default 1.2, changing that to ~0.8 will reduced the
Phase error considerably
4) The default TC setting (Time Constant) of 100 sec is about right for now,
but later if you fix the Osc tempco issue, you'll improve things by
changing that to ~ 300 sec
(If you just changed the TC from 100 to 300 now it would make things worse)
5) change the ADEV data plot to a "SAS" antenna survey plot to make sure
there are no blind spots or multipath signals
The SAS plot will help tell where your EL and AMU should be set. ( they are
set OK for now)
5a) The average sat count of 6 with a low of 4 shows your antenna has a
good basic view of the sky. (no problem there)
6) your Holdover is still at 0 seconds, This is good, it means you never go
into hold over.
7) Dac voltage at -.6xx is fine and seems to of stabilized well from your
first plot that had a lot of initial turn-on drifting.
8) main problem and the first thing to improve, is the Oscillators tempco
To better see it, manually change the gain and offset of the Temp plot, and
you will see how well it lines up with the Dac plot.
> Trying to understand why the PPS trace is doing what it is doing.
>Looks like it might have something to do with the temperature.
Correct, The PPS is doing what it is doing because it is tracking the slope
of the DAC which in turn is directly tracking the Temp change of the sensor.
Several ways to help it, how you do that with your dual temp control will be
a nice learning experience.
bottom line is:
Don't let the temp change so much. and/or
make the Osc less sensitive to the temp change
other setup hints
a) Helps if something goes wrong if you turn on "Log" so you do not loose
the plot info.
b) set the display Q to 30 days, so you can compare the before and after
effects of any change you do, all on screen at the same time.
c) turn off the ADEV plots and data display, They are not adding any useful
info at this time.
Garren Davis posted:
Thanks for the comments. I've included a 34 hour screen dump. Trying to
the PPS trace is doing what it is doing. Looks like it might have something
to do with
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.
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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