Empathy List Archives

DJ

Didier Juges

Sun, Oct 22, 2006 2:34 PM

Hi Warner,

Does it mean I should divide the 10 MHz down to 1 Hz output and use the
5370 to measure TI compared to it's internal timebase once per second,
and feed that to the computer, store it to a file and feed the output to
AlaVar? (obviously, the divider would have to use synchronous counters)

Or should I work directly on the 10 MHz output? The 5370 can average up
to 100k samples, so by averaging 100k samples and polling the GPIB
once/sec, would I be correct if I use the computer to average those
further down to 2/sec, 4/sec and so on as needed before feeding the data
to Alavar?

Now, let's assume I have a big hard drive (250 GB + 120 GB at the
moment, with probably close to a total of 200 GB available), other than
computing time (which may not be negligible), how can I determine the
best acquisition interval? (as the one that will give me meaningful data
in the shortest amount of time)

I understand AlaVar only works in batch mode (no real time capability),
so I have to collect a certain amount of data "blindly" before I can
find out if it is any good. If I am checking a GPS disciplined
oscillator, that will take several hours at a time and I am trying to
speed up the process, at least to make sure the procedures and
algorithms are OK.

See, you can't provide answers without getting more questions :-)

Thanks

Didier

M. Warner Losh wrote:

Just a quick note on this topic. I'll not be able to answer all your
questions, but here's a few.

Allen Variance (or Allen Deviation) is usually used to measure clock
stability over 1s or longer. As this is a way to judge the stability
of an oscillator, very short term numbers tend to be less useful.
This means that fast data collection rates end up having lots of
redundant data that contributes little added benefit to the
calculations, but has large storage requirements. If you are
computing a Tau of 100s, for example, 10Hz vs 1Hz data will only give
a factor of 3 better confidence interval (the standard deviation of
the avarage at a Tau of 100s, which goes as the square root of the
number of samples), but you'd have a 10x increase in storage.

Allen Variance usually is measured at 1s, 2s, 4 (or 5s), 10s, 20s,
etc up to some fraction of the period of time the data covers. The
fraction is again determined by the type of deviation and the number
of points used to calculate the number.

Warner

Hi Warner, Does it mean I should divide the 10 MHz down to 1 Hz output and use the 5370 to measure TI compared to it's internal timebase once per second, and feed that to the computer, store it to a file and feed the output to AlaVar? (obviously, the divider would have to use synchronous counters) Or should I work directly on the 10 MHz output? The 5370 can average up to 100k samples, so by averaging 100k samples and polling the GPIB once/sec, would I be correct if I use the computer to average those further down to 2/sec, 4/sec and so on as needed before feeding the data to Alavar? Now, let's assume I have a big hard drive (250 GB + 120 GB at the moment, with probably close to a total of 200 GB available), other than computing time (which may not be negligible), how can I determine the best acquisition interval? (as the one that will give me meaningful data in the shortest amount of time) I understand AlaVar only works in batch mode (no real time capability), so I have to collect a certain amount of data "blindly" before I can find out if it is any good. If I am checking a GPS disciplined oscillator, that will take several hours at a time and I am trying to speed up the process, at least to make sure the procedures and algorithms are OK. See, you can't provide answers without getting more questions :-) Thanks Didier M. Warner Losh wrote: > Just a quick note on this topic. I'll not be able to answer all your > questions, but here's a few. > > Allen Variance (or Allen Deviation) is usually used to measure clock > stability over 1s or longer. As this is a way to judge the stability > of an oscillator, very short term numbers tend to be less useful. > This means that fast data collection rates end up having lots of > redundant data that contributes little added benefit to the > calculations, but has large storage requirements. If you are > computing a Tau of 100s, for example, 10Hz vs 1Hz data will only give > a factor of 3 better confidence interval (the standard deviation of > the avarage at a Tau of 100s, which goes as the square root of the > number of samples), but you'd have a 10x increase in storage. > > Allen Variance usually is measured at 1s, 2s, 4 (or 5s), 10s, 20s, > etc up to some fraction of the period of time the data covers. The > fraction is again determined by the type of deviation and the number > of points used to calculate the number. > > Warner > >

JA

John Ackermann N8UR

Sun, Oct 22, 2006 2:57 PM

Didier, a few comments embedded below.

John

Didier Juges said the following on 10/22/2006 10:34 AM:

Hi Warner,

Does it mean I should divide the 10 MHz down to 1 Hz output and use the
5370 to measure TI compared to it's internal timebase once per second,
and feed that to the computer, store it to a file and feed the output to
AlaVar? (obviously, the divider would have to use synchronous counters)

Or should I work directly on the 10 MHz output? The 5370 can average up
to 100k samples, so by averaging 100k samples and polling the GPIB
once/sec, would I be correct if I use the computer to average those
further down to 2/sec, 4/sec and so on as needed before feeding the data
to Alavar?

Ideally, you want to reduce both the device under test (DUT) and the
reference to 1 PPS. The GPS can give you that directly, and you can use
some sort of divider to reduce the DUT from its nominal frequency. Not
everyone does it the same way, but there seems to be a convention that
the reference signal is applied to the "stop" input of the counter, and
the DUT to the "start" input. You want to bump the phase of the pulses
so that the initial time difference is relatively small -- ideally, not
more than a few hundred microseconds. This will reduce the impact of
any noise or offset in the counter's reference.

It's possible to use 1PPS from the reference, and a higher frequency
(even 10MHz) from the DUT, but I've never had a lot of luck doing this.
It's way too easy to slip a cycle and get artificial phase jumps.

Now, let's assume I have a big hard drive (250 GB + 120 GB at the
moment, with probably close to a total of 200 GB available), other than
computing time (which may not be negligible), how can I determine the
best acquisition interval? (as the one that will give me meaningful data
in the shortest amount of time)

Even with the 5370's 20ps resolution, you won't be able to measure good
DUTs below about 100 seconds averaging; the trigger jitter and other
noise will get you unless you go to something sophisticated like a
dual-mixer time-difference system (which isn't as easy to implement as
it appears at first glance).

So, I normally average data for 100 seconds and then log those averages.
You can use the counter's internal average command, or just capture
each data point and average in your software. I output a data file with
the MJD and phase value. That data file then feeds whatever analysis
tool I'm using at the moment.

I understand AlaVar only works in batch mode (no real time capability),
so I have to collect a certain amount of data "blindly" before I can
find out if it is any good. If I am checking a GPS disciplined
oscillator, that will take several hours at a time and I am trying to
speed up the process, at least to make sure the procedures and
algorithms are OK.

This is an avocation for the patient. :-) My current experiment logging
2 HP5061As and an HP5065A against GPS has been running for about 90 days
now, and I hope to get at least another 30 days before I have to stop to
make some equipment changes.

John

Didier, a few comments embedded below. John ---- Didier Juges said the following on 10/22/2006 10:34 AM: > Hi Warner, > > Does it mean I should divide the 10 MHz down to 1 Hz output and use the > 5370 to measure TI compared to it's internal timebase once per second, > and feed that to the computer, store it to a file and feed the output to > AlaVar? (obviously, the divider would have to use synchronous counters) > > Or should I work directly on the 10 MHz output? The 5370 can average up > to 100k samples, so by averaging 100k samples and polling the GPIB > once/sec, would I be correct if I use the computer to average those > further down to 2/sec, 4/sec and so on as needed before feeding the data > to Alavar? Ideally, you want to reduce both the device under test (DUT) and the reference to 1 PPS. The GPS can give you that directly, and you can use some sort of divider to reduce the DUT from its nominal frequency. Not everyone does it the same way, but there seems to be a convention that the reference signal is applied to the "stop" input of the counter, and the DUT to the "start" input. You want to bump the phase of the pulses so that the initial time difference is relatively small -- ideally, not more than a few hundred microseconds. This will reduce the impact of any noise or offset in the counter's reference. It's possible to use 1PPS from the reference, and a higher frequency (even 10MHz) from the DUT, but I've never had a lot of luck doing this. It's way too easy to slip a cycle and get artificial phase jumps. > Now, let's assume I have a big hard drive (250 GB + 120 GB at the > moment, with probably close to a total of 200 GB available), other than > computing time (which may not be negligible), how can I determine the > best acquisition interval? (as the one that will give me meaningful data > in the shortest amount of time) Even with the 5370's 20ps resolution, you won't be able to measure good DUTs below about 100 seconds averaging; the trigger jitter and other noise will get you unless you go to something sophisticated like a dual-mixer time-difference system (which isn't as easy to implement as it appears at first glance). So, I normally average data for 100 seconds and then log those averages. You can use the counter's internal average command, or just capture each data point and average in your software. I output a data file with the MJD and phase value. That data file then feeds whatever analysis tool I'm using at the moment. > I understand AlaVar only works in batch mode (no real time capability), > so I have to collect a certain amount of data "blindly" before I can > find out if it is any good. If I am checking a GPS disciplined > oscillator, that will take several hours at a time and I am trying to > speed up the process, at least to make sure the procedures and > algorithms are OK. This is an avocation for the patient. :-) My current experiment logging 2 HP5061As and an HP5065A against GPS has been running for about 90 days now, and I hope to get at least another 30 days before I have to stop to make some equipment changes. John

DJ

Didier Juges

Sun, Oct 22, 2006 5:41 PM

More comments embedded...

Didier

John Ackermann N8UR wrote:

Didier, a few comments embedded below.

John

Didier Juges said the following on 10/22/2006 10:34 AM:

Hi Warner,

Does it mean I should divide the 10 MHz down to 1 Hz output and use the
5370 to measure TI compared to it's internal timebase once per second,
and feed that to the computer, store it to a file and feed the output to
AlaVar? (obviously, the divider would have to use synchronous counters)

Or should I work directly on the 10 MHz output? The 5370 can average up
to 100k samples, so by averaging 100k samples and polling the GPIB
once/sec, would I be correct if I use the computer to average those
further down to 2/sec, 4/sec and so on as needed before feeding the data
to Alavar?

Ideally, you want to reduce both the device under test (DUT) and the
reference to 1 PPS. The GPS can give you that directly, and you can use
some sort of divider to reduce the DUT from its nominal frequency. Not
everyone does it the same way, but there seems to be a convention that
the reference signal is applied to the "stop" input of the counter, and
the DUT to the "start" input. You want to bump the phase of the pulses
so that the initial time difference is relatively small -- ideally, not
more than a few hundred microseconds. This will reduce the impact of
any noise or offset in the counter's reference.

It's possible to use 1PPS from the reference, and a higher frequency
(even 10MHz) from the DUT, but I've never had a lot of luck doing this.
It's way too easy to slip a cycle and get artificial phase jumps.

From your comment, I gather that if the oscillators to be compared are
not on the same frequency, problem might ensue, so the 1 PPS output is a
much better option than the 10 MHz.
If I use a 1 PPS signal for both oscillators, as long as they do not
drift by 1 cycle during the sample period, we should be OK.

So the best would be to be able to reset the divider (that takes the
crystal down to 1 PPS) synchronously (or with a small delay) with the 1
PPS output of the GPS, then I should be good for a while. If I get the
OCXO within 10-6, I should be good for 10^6 seconds before skipping a
cycle (assuming the drift is in the proper direction....)

Now, let's assume I have a big hard drive (250 GB + 120 GB at the
moment, with probably close to a total of 200 GB available), other than
computing time (which may not be negligible), how can I determine the
best acquisition interval? (as the one that will give me meaningful data
in the shortest amount of time)

Even with the 5370's 20ps resolution, you won't be able to measure good
DUTs below about 100 seconds averaging; the trigger jitter and other
noise will get you unless you go to something sophisticated like a
dual-mixer time-difference system (which isn't as easy to implement as
it appears at first glance).

So, I normally average data for 100 seconds and then log those averages.
You can use the counter's internal average command, or just capture
each data point and average in your software. I output a data file with
the MJD and phase value. That data file then feeds whatever analysis
tool I'm using at the moment.

So every 100 seconds, you log the average data collected at the 1 PPS
rate, for a few months.
How long before you have something that is at least worth looking at
just to make sure it is working?
(my type A personality does not deal with experiments lasting months too
well :-)
I remember seeing some postings about MJD being in a particular format.
I will look in the AvaTar help file, I believe I saw something about that.
A sample file would be helpful.

So I gather this procedure will measure the sum of the variations of
both oscillators. By using three oscillators, and measuring them 2 at a
time, after 3 measurement cycles, I should be able to determine the
performance of each oscillator. At least that's all I remember of
statistics classes. How to do that escapes me at the moment.

Maybe it would be simpler to buy an FRK Rubidium oscillator on eBay. How
do these compare to a 10811 in the short term and the long term?

I understand AlaVar only works in batch mode (no real time capability),
so I have to collect a certain amount of data "blindly" before I can
find out if it is any good. If I am checking a GPS disciplined
oscillator, that will take several hours at a time and I am trying to
speed up the process, at least to make sure the procedures and
algorithms are OK.

This is an avocation for the patient. :-) My current experiment logging
2 HP5061As and an HP5065A against GPS has been running for about 90 days
now, and I hope to get at least another 30 days before I have to stop to
make some equipment changes.

Roger that, see my comment above.
I have an older laptop and spare GPIB/serial controller that I can
dedicate to the task. I will set that aside so I am not tempted to mess
with it while it collects data.
I must make sure my battery backup system is working (the 5370A draws
200 VA), and I'll be listening to 6m in the mean time (talking about
patience :-)

John

Thanks a lot

Didier

More comments embedded... Didier John Ackermann N8UR wrote: > Didier, a few comments embedded below. > > John > ---- > > Didier Juges said the following on 10/22/2006 10:34 AM: > >> Hi Warner, >> >> Does it mean I should divide the 10 MHz down to 1 Hz output and use the >> 5370 to measure TI compared to it's internal timebase once per second, >> and feed that to the computer, store it to a file and feed the output to >> AlaVar? (obviously, the divider would have to use synchronous counters) >> >> Or should I work directly on the 10 MHz output? The 5370 can average up >> to 100k samples, so by averaging 100k samples and polling the GPIB >> once/sec, would I be correct if I use the computer to average those >> further down to 2/sec, 4/sec and so on as needed before feeding the data >> to Alavar? >> > > Ideally, you want to reduce both the device under test (DUT) and the > reference to 1 PPS. The GPS can give you that directly, and you can use > some sort of divider to reduce the DUT from its nominal frequency. Not > everyone does it the same way, but there seems to be a convention that > the reference signal is applied to the "stop" input of the counter, and > the DUT to the "start" input. You want to bump the phase of the pulses > so that the initial time difference is relatively small -- ideally, not > more than a few hundred microseconds. This will reduce the impact of > any noise or offset in the counter's reference. > > It's possible to use 1PPS from the reference, and a higher frequency > (even 10MHz) from the DUT, but I've never had a lot of luck doing this. > It's way too easy to slip a cycle and get artificial phase jumps. > > From your comment, I gather that if the oscillators to be compared are not on the same frequency, problem might ensue, so the 1 PPS output is a much better option than the 10 MHz. If I use a 1 PPS signal for both oscillators, as long as they do not drift by 1 cycle during the sample period, we should be OK. So the best would be to be able to reset the divider (that takes the crystal down to 1 PPS) synchronously (or with a small delay) with the 1 PPS output of the GPS, then I should be good for a while. If I get the OCXO within 10-6, I should be good for 10^6 seconds before skipping a cycle (assuming the drift is in the proper direction....) >> Now, let's assume I have a big hard drive (250 GB + 120 GB at the >> moment, with probably close to a total of 200 GB available), other than >> computing time (which may not be negligible), how can I determine the >> best acquisition interval? (as the one that will give me meaningful data >> in the shortest amount of time) >> > > Even with the 5370's 20ps resolution, you won't be able to measure good > DUTs below about 100 seconds averaging; the trigger jitter and other > noise will get you unless you go to something sophisticated like a > dual-mixer time-difference system (which isn't as easy to implement as > it appears at first glance). > > So, I normally average data for 100 seconds and then log those averages. > You can use the counter's internal average command, or just capture > each data point and average in your software. I output a data file with > the MJD and phase value. That data file then feeds whatever analysis > tool I'm using at the moment. > > > So every 100 seconds, you log the average data collected at the 1 PPS rate, for a few months. How long before you have something that is at least worth looking at just to make sure it is working? (my type A personality does not deal with experiments lasting months too well :-) I remember seeing some postings about MJD being in a particular format. I will look in the AvaTar help file, I believe I saw something about that. A sample file would be helpful. So I gather this procedure will measure the sum of the variations of both oscillators. By using three oscillators, and measuring them 2 at a time, after 3 measurement cycles, I should be able to determine the performance of each oscillator. At least that's all I remember of statistics classes. How to do that escapes me at the moment. Maybe it would be simpler to buy an FRK Rubidium oscillator on eBay. How do these compare to a 10811 in the short term and the long term? >> I understand AlaVar only works in batch mode (no real time capability), >> so I have to collect a certain amount of data "blindly" before I can >> find out if it is any good. If I am checking a GPS disciplined >> oscillator, that will take several hours at a time and I am trying to >> speed up the process, at least to make sure the procedures and >> algorithms are OK. >> > > This is an avocation for the patient. :-) My current experiment logging > 2 HP5061As and an HP5065A against GPS has been running for about 90 days > now, and I hope to get at least another 30 days before I have to stop to > make some equipment changes. > > Roger that, see my comment above. I have an older laptop and spare GPIB/serial controller that I can dedicate to the task. I will set that aside so I am not tempted to mess with it while it collects data. I must make sure my battery backup system is working (the 5370A draws 200 VA), and I'll be listening to 6m in the mean time (talking about patience :-) > John > > Thanks a lot Didier

X

xaos

Sun, Oct 22, 2006 6:42 PM

Hello everyone,

I have, until now, resisted the urge to buy a GPS navigation system for
my car.
However, I now have to do some traveling and new and unknown addresses
keep popping up.

There are several different GPS units on the market and they all look OK
(i guess).

I just want to know which units do the members here consider to be the
best for
this sort of thing?

Many thanks in advance,

-George Hrysanthopoulos, N2FGX

Hello everyone, I have, until now, resisted the urge to buy a GPS navigation system for my car. However, I now have to do some traveling and new and unknown addresses keep popping up. There are several different GPS units on the market and they all look OK (i guess). I just want to know which units do the members here consider to be the best for this sort of thing? Many thanks in advance, -George Hrysanthopoulos, N2FGX

RK

Rob Kimberley

Sun, Oct 22, 2006 9:19 PM

George,

I have been happily using a Garmin Quest for about three years now. There
are of course newer versions from this manufacturer, who have a very good
reputation. Tom-Tom are also very popular in the UK, but have no experience
of using them.

Good hunting!

Rob Kimberley

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of xaos
Sent: 22 October 2006 19:42
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] GPS unit for car navigation -OT ??

Hello everyone,

I have, until now, resisted the urge to buy a GPS navigation system for my
car.
However, I now have to do some traveling and new and unknown addresses keep
popping up.

There are several different GPS units on the market and they all look OK (i
guess).

I just want to know which units do the members here consider to be the best
for this sort of thing?

Many thanks in advance,

-George Hrysanthopoulos, N2FGX

time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

George, I have been happily using a Garmin Quest for about three years now. There are of course newer versions from this manufacturer, who have a very good reputation. Tom-Tom are also very popular in the UK, but have no experience of using them. Good hunting! Rob Kimberley -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of xaos Sent: 22 October 2006 19:42 To: Discussion of precise time and frequency measurement Subject: [time-nuts] GPS unit for car navigation -OT ?? Hello everyone, I have, until now, resisted the urge to buy a GPS navigation system for my car. However, I now have to do some traveling and new and unknown addresses keep popping up. There are several different GPS units on the market and they all look OK (i guess). I just want to know which units do the members here consider to be the best for this sort of thing? Many thanks in advance, -George Hrysanthopoulos, N2FGX _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

JM

James Maynard

Sun, Oct 22, 2006 11:12 PM

xaos wrote:

Hello everyone,

I have, until now, resisted the urge to buy a GPS navigation system for
my car.
However, I now have to do some traveling and new and unknown addresses
keep popping up.

There are several different GPS units on the market and they all look OK
(i guess).

I just want to know which units do the members here consider to be the
best for
this sort of thing?

Many thanks in advance,

-George Hrysanthopoulos, N2FGX

I really like my Garmin StreetPilot 7200. Its GPS receiver has WAAS
correction capability, it has a built-in database of street maps for the
entire USA, and its large display, perched atop the dashboard of my car,
is very readable to my aging eyes. In my car, my view of the
speedometer is obscured by the steering wheel, so I use the GPS receiver
as my primary speedometer display, too.

I usually set it just to display a moving map. In that mode, it shows
the name of the next cross-street that I will encounter at the top of
the screen -- much easier to read with my aging eyes than the street
sign on the corner! It also shows my speed and the time of day.

Occasionally I will set it to compute a route for me to follow,
particularly when driving to someplace unfamiliar. In that mode, it
doesn't display the time of day, but instead displays the estimated time
of arrival at the distination -- something that I'm not as interested in
knowing. At intersections where the calculated route changes from one
street or highway to another, it zooms in automatically as I approach
the intersection and zooms out automatically after making the turn.

It didn't hurt that, as a Garmin employee, I got a nice employee discount!

James Maynard, K7KK
Salem, Oregon, USA

xaos wrote: > Hello everyone, > > I have, until now, resisted the urge to buy a GPS navigation system for > my car. > However, I now have to do some traveling and new and unknown addresses > keep popping up. > > There are several different GPS units on the market and they all look OK > (i guess). > > I just want to know which units do the members here consider to be the > best for > this sort of thing? > > Many thanks in advance, > > -George Hrysanthopoulos, N2FGX I really like my Garmin StreetPilot 7200. Its GPS receiver has WAAS correction capability, it has a built-in database of street maps for the entire USA, and its large display, perched atop the dashboard of my car, is very readable to my aging eyes. In my car, my view of the speedometer is obscured by the steering wheel, so I use the GPS receiver as my primary speedometer display, too. I usually set it just to display a moving map. In that mode, it shows the name of the next cross-street that I will encounter at the top of the screen -- much easier to read with my aging eyes than the street sign on the corner! It also shows my speed and the time of day. Occasionally I will set it to compute a route for me to follow, particularly when driving to someplace unfamiliar. In that mode, it doesn't display the time of day, but instead displays the estimated time of arrival at the distination -- something that I'm not as interested in knowing. At intersections where the calculated route changes from one street or highway to another, it zooms in automatically as I approach the intersection and zooms out automatically after making the turn. It didn't hurt that, as a Garmin employee, I got a nice employee discount! ---- James Maynard, K7KK Salem, Oregon, USA

DB

Dr Bruce Griffiths

Sun, Oct 22, 2006 11:19 PM

Didier Juges wrote: