Hi Didier,

you may use the DRIFT section of the graphic editor of PLOTTER to remove
a phase drift due to a constant frequency offset as seen in this data,
with the result that you get more "visual resolution" out of it, as in
the attached PDF.

73 de Ulrich, DF6JB

http://www.ko4bb.com/Test_Equipment/HP10811-GPS-10-29.png

(sorry the screen shot is cropped at the bottom)
and the data file is at

http://www.ko4bb.com/Test_Equipment/HP10811-GPS-10-29.dat

Didier KO4BB

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I had to stack up frequency counters on top of frequency counters (to
measure time difference and each input frequency simultaneously -> 3
counters) and the last one on the top, a HP 5334B, was fairly high and
just about level with the antenna, about 2 feet away. I found out that
if I stood in line with the antenna and the counter, my shadow would
significantly affect the cleanliness of the 1 PPS, so I moved the
antenna just under the ceiling and the problem went away.

Amazing!

Didier

Rob Kimberley wrote:

Ulrich Bangert wrote:

Ulrich,

I ran the OCXO with the new antenna location overnight, except that the
laptop went to sleep some time in the night, so I have lost several
hours of data, which may explain the sudden slope change in the plot
below (I need to save timestamps I guess). However, the remaining data
is good I think. There was no sudden noise, and about 5 phase jumps due
to the OCXO drifting during the observation period.

I downloaded the latest version of Plotter (10-27) and it's all there. I
was able to quickly remove the phase jumps when the OCXO drifted past
the divided down period, and then remove the remaining slow drift.

What a nice piece of software!
(even the menu now has a normal File->Open :-)

The latest plots are at the usual place:
http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2.png
http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2_Allan.png

Now that the data collection method seems to be getting close, I wonder
how I should use the data, and what it means.

The Allan deviation seems to taper around e-10 at 1000 seconds, then it
looks like it wants to keep getting lower.

As a reminder, this is the HP10811 against the GPS receiver. I am not
sure what I should expect?

Didier

PS: I am still planning to measure ambient temperature at the same time
as I collect TI, via the GPIB, using a HP 3478A voltmeter and a
thermistor. This way, I should be able to correlate frequency changes
and temperature changes. I assume I can tell Plotter to ignore the
temperature field or display it with its own scaling. Should I use a
specific character as field delimiter? (such as a comma, or just spaces?)

(In the short term, temperature data will be thermistor values, until I
write the code to convert in degrees. )

Also, if I use time stamps, should I use field delimiter between the
time stamp and the data?

What is the time stamps are discontinuous (as if the laptop falls asleep
again), will that mess up Plotter?

Didier,

you take the credit for this!

73 de Ulrich, DF6JB

http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2_Allan.png

Now that the data collection method seems to be getting close, I wonder
how I should use the data, and what it means.

The Allan deviation seems to taper around e-10 at 1000 seconds, then it
looks like it wants to keep getting lower.

As a reminder, this is the HP10811 against the GPS receiver. I am not
sure what I should expect?

Didier

PS: I am still planning to measure ambient temperature at the same time
as I collect TI, via the GPIB, using a HP 3478A voltmeter and a
thermistor. This way, I should be able to correlate frequency changes
and temperature changes. I assume I can tell Plotter to ignore the
temperature field or display it with its own scaling. Should I use a
specific character as field delimiter? (such as a comma, or just
spaces?)

(In the short term, temperature data will be thermistor values, until I
write the code to convert in degrees. )

Also, if I use time stamps, should I use field delimiter between the
time stamp and the data?

What is the time stamps are discontinuous (as if the laptop falls asleep

again), will that mess up Plotter?

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Didier Juges wrote:

Didier

Unless you have a particularly poor 10811 it is likely that the measured
Allan deviation is limited by your the instability of your GPS receiver
PPS output.
With a good GPS timing receiver setup you should expect an Allan
variance perhaps 5x lower than this as illustrated in Ulrich's article
for the AMSAT journal.

Bruce

Dr Bruce Griffiths wrote:

Thank you Bruce, that is the kind of information I was looking for. The
Jupiter will have to do for now, I have two of the same model. I may try
a better antenna though.
I got a link to the gpskit.nl web page, with a lot of information on the
Jupiter, through an off-list message, and I will experiment with the
settings in the receiver (mask angle primarily)

It seems all I have left to do is find the best way to close the loop
(!) and try again against another 10811. I also still have a lot of
experimentation to do over temperature, and check the stability of my
distribution amplifier.

I have learned a lot in the last few days, thanks to everyone on
time-nuts who took the time to explain the details to me.

I have a lot left to learn and experiment with, but at least I am aiming
in the right direction :-)

Didier KO4BB