Empathy List Archives

time-nuts@lists.febo.com

Discussion of precise time and frequency measurement

Predicting clock stability from the various characterization methods

n3izn@aol.com

Fri, Dec 1, 2006 7:46 PM

Hello new to the list and I have some questions about a GPS disciplined(?) 10 Mhz oscillator I acquired. Wondering if you guys could help. I was referred to this list from the microwave group.

I’m cleaning out a site that was vandalized when I came across a piece of equipment that had a GPS in, 10 Mhz and 1 PPS out. Along with some other functions. So I saved it from the dumpster.

I power it up and hook it to an external GPS antenna. Yes I have 5 volts on the line to power the antenna. After several hours it never locked up. I’ve seen these units in other sites and now how they react when powered back up. The unit is noisy and draws a lot of juice, about 6 amps @ -48VDC Since I don’t need all that other crap in the box I opened it up to see if there was a separate module, sure enough there was.

The module is about 3X5”, powered by +14 VDC, had the GPS in and 10 MHZ/1PPS out along with 2 other pin-type connectors. Only 1 of the pin-type connectors was being used I’m guessing that is how it talks to the rest of the equipment. The other pin-type connector I’m guessing is for maintenance or trouble shooting.

After a close up look I notice the chip next to the unused pin-type connector is the same chip used by these ham kits to convert the TTL data from GPS engines to RS-232. I’m able to trace it out to the pins and find RS232 out/in. This is the message I got:

$GETVER 9.1.10 BOOT 10 6286 3bf5 06162200C1000A200627A1E0

It repeats over and over. I left it on for over a day and still the same thing. The 10 Mhz never stabilizes.

I’m powering it off of 14 volts and it starts off drawing about 1 amp, after a few minutes it drops to about a ¼ amp. That appears to be the OXCO warming up.

OK so here come the speculations and questions.

It’s been suggested that since the GPS is not mobile but in a fixed location, it has been told where it is or allowed to find itself then it will not search any more. I’m over a 100 miles away from where it came from It will never lock up?

Does the above string look like a message from the GPS or from other components on the board?

Almost forgot the GPS engine is a “Furuno GT-8031”

Any one have experience with this engine?

Do you think I should be able to give it a command or do a hardware reset to lock up in it’s new location?

I would like to have this for the 10 Mhz out, NEMA data for syncing PC time and grid square would be a plus.

Sorry for the long email on first posting. Any help would be appreciated.

Chris

Check out the new AOL. Most comprehensive set of free safety and security tools, free access to millions of high-quality videos from across the web, free AOL Mail and more.

Hello new to the list and I have some questions about a GPS disciplined(?) 10 Mhz oscillator I acquired. Wondering if you guys could help. I was referred to this list from the microwave group. I’m cleaning out a site that was vandalized when I came across a piece of equipment that had a GPS in, 10 Mhz and 1 PPS out. Along with some other functions. So I saved it from the dumpster. I power it up and hook it to an external GPS antenna. Yes I have 5 volts on the line to power the antenna. After several hours it never locked up. I’ve seen these units in other sites and now how they react when powered back up. The unit is noisy and draws a lot of juice, about 6 amps @ -48VDC Since I don’t need all that other crap in the box I opened it up to see if there was a separate module, sure enough there was. The module is about 3X5”, powered by +14 VDC, had the GPS in and 10 MHZ/1PPS out along with 2 other pin-type connectors. Only 1 of the pin-type connectors was being used I’m guessing that is how it talks to the rest of the equipment. The other pin-type connector I’m guessing is for maintenance or trouble shooting. After a close up look I notice the chip next to the unused pin-type connector is the same chip used by these ham kits to convert the TTL data from GPS engines to RS-232. I’m able to trace it out to the pins and find RS232 out/in. This is the message I got: $GETVER 9.1.10 BOOT 10 6286 3bf5 06162200C1000A200627A1E0 It repeats over and over. I left it on for over a day and still the same thing. The 10 Mhz never stabilizes. I’m powering it off of 14 volts and it starts off drawing about 1 amp, after a few minutes it drops to about a ¼ amp. That appears to be the OXCO warming up. OK so here come the speculations and questions. It’s been suggested that since the GPS is not mobile but in a fixed location, it has been told where it is or allowed to find itself then it will not search any more. I’m over a 100 miles away from where it came from It will never lock up? Does the above string look like a message from the GPS or from other components on the board? Almost forgot the GPS engine is a “Furuno GT-8031” Any one have experience with this engine? Do you think I should be able to give it a command or do a hardware reset to lock up in it’s new location? I would like to have this for the 10 Mhz out, NEMA data for syncing PC time and grid square would be a plus. Sorry for the long email on first posting. Any help would be appreciated. Chris ________________________________________________________________________ Check out the new AOL. Most comprehensive set of free safety and security tools, free access to millions of high-quality videos from across the web, free AOL Mail and more.

Jason Rabel

Fri, Dec 1, 2006 8:07 PM

Welcome! I'm new here too, but the people here are most helpful and
friendly.

There are other guys here that can probably give you a lot better info, but
until they reply I'll try to give my two bits from the info you gave.

First about the static position. Since those units you said were at other
sites, I would assume they would do a self-survey upon power up (and GPS
fix) as opposed to requiring someone to manually program in the position.
Also even if the location changed it should still be able to pickup the
satellite signals.

I'm not familiar with that GPS engine, I just looked it up on their site (
http://www.furunogps.com/GT8031_image.html ), neat little thing. It says
acquisition from cold start in 44.9 seconds. Most GPSes I've seen will give
a proprietary sentence upon power-up, stating the firmware version and other
bits of info. However with it looping like that, maybe something is
connected to it that shouldn't be, causing it to constantly do like a
soft-reboot?

Maybe you can find some info on the Furuno site about sending a reset or
other command? Some GPSes I've seen (like the Motorola Oncore) start in a
poll only mode, meaning it doesn't give any info until you send commands for
it to do so. So it might just be giving that proprietary sentence once a
second until you request other info?

Jason

Welcome! I'm new here too, but the people here are most helpful and friendly. There are other guys here that can probably give you a lot better info, but until they reply I'll try to give my two bits from the info you gave. First about the static position. Since those units you said were at other sites, I would assume they would do a self-survey upon power up (and GPS fix) as opposed to requiring someone to manually program in the position. Also even if the location changed it should still be able to pickup the satellite signals. I'm not familiar with that GPS engine, I just looked it up on their site ( http://www.furunogps.com/GT8031_image.html ), neat little thing. It says acquisition from cold start in 44.9 seconds. Most GPSes I've seen will give a proprietary sentence upon power-up, stating the firmware version and other bits of info. However with it looping like that, maybe something is connected to it that shouldn't be, causing it to constantly do like a soft-reboot? Maybe you can find some info on the Furuno site about sending a reset or other command? Some GPSes I've seen (like the Motorola Oncore) start in a poll only mode, meaning it doesn't give any info until you send commands for it to do so. So it might just be giving that proprietary sentence once a second until you request other info? Jason

Jason Rabel

Fri, Dec 1, 2006 8:10 PM

Oh, I accidentally linked to the wrong page... Here's the main one:

http://www.furunogps.com/GT8031.html

Some interesting tidbits about it:

Low cost but powerful, fast 16 Channel GPS receiver
Accuracy is not sacrificed 15 nanoseconds with regard to UTC (1 sigma)
Low power consumption (58mA@3.3VDC) at full tracking satellites
RF pig tail cable with popular connector already soldered for easier, more
cost-effective installation
Almanac uploading and downloading
Autonomous transition from "Survey" to "Fixed Observation Point" lets the
receiver calculate its position and then use the averaged position as the
fixed observation point
"Back to fixed position set" allows you to go back to the fixed position
even after power-off

Oh, I accidentally linked to the wrong page... Here's the main one: http://www.furunogps.com/GT8031.html Some interesting tidbits about it: * Low cost but powerful, fast 16 Channel GPS receiver * Accuracy is not sacrificed 15 nanoseconds with regard to UTC (1 sigma) * Low power consumption (58mA@3.3VDC) at full tracking satellites * RF pig tail cable with popular connector already soldered for easier, more cost-effective installation * Almanac uploading and downloading * Autonomous transition from "Survey" to "Fixed Observation Point" lets the receiver calculate its position and then use the averaged position as the fixed observation point * "Back to fixed position set" allows you to go back to the fixed position even after power-off

Dr Bruce Griffiths

Fri, Dec 1, 2006 11:24 PM

Tom Van Baak wrote:

Brooke,

Maybe this helps. The clock prediction into the future
is based on the past history and the current point. If
the measured ADEV for a clock is, say 1e-13, for a
measurement interval of 1 day (tau), then the prediction,
within one standard deviation, is that you'll be within
1e-13 tomorrow. 1e-13 at one day is about 9 ns. I think
this is right. Can someone double check?

It shouldn't matter what your divider does -- 9 ns of
time error is 9 ns regardless if it's the zero-crossing
of a 5 MHz RF output of the leading edge of a 1PPS
signal.

A divider postpones cycle wrapping but doesn't affect
clock accuracy or stability (other than the obvious
introduction of passive & active component noise in
the signal path).

/tvb

----- Original Message -----
From: Brooke Clarke
To: Tom Van Baak ; Discussion of precise time and frequency measurement
Sent: Thursday, November 30, 2006 13:31
Subject: Re: [time-nuts] Predicting clock stability from
thevariouscharacterizationmethods

Hi Tom:

Is there a way to use the Allan plot to predict the variation in a reading?
For example if you use the plot comparing the 1 PPS from a GPS receiver to a
good Cesium frequency standard, then:
(1) what size of variation would you expect if the Cesium standard was
divided down to 1 kHz and that was compared to the GPS 1 PPS, or
(2) what size of variation would you expect if the Cesium standard was
divided down to 1 Pulse/1,000 seconds?

Have Fun,

Brooke Clarke

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

Tom

Surely the time standard deviation should be:

TDEV = TAU*MODADEV(TAU)/SQRT(3) ??

At least this appears to be so in the link you gave:

http://www.wriley.com/paper2ht.htm

Bruce

Tom Van Baak wrote: > Brooke, > > Maybe this helps. The clock prediction into the future > is based on the past history and the current point. If > the measured ADEV for a clock is, say 1e-13, for a > measurement interval of 1 day (tau), then the prediction, > within one standard deviation, is that you'll be within > 1e-13 tomorrow. 1e-13 at one day is about 9 ns. I think > this is right. Can someone double check? > > It shouldn't matter what your divider does -- 9 ns of > time error is 9 ns regardless if it's the zero-crossing > of a 5 MHz RF output of the leading edge of a 1PPS > signal. > > A divider postpones cycle wrapping but doesn't affect > clock accuracy or stability (other than the obvious > introduction of passive & active component noise in > the signal path). > > /tvb > > ----- Original Message ----- > From: Brooke Clarke > To: Tom Van Baak ; Discussion of precise time and frequency measurement > Sent: Thursday, November 30, 2006 13:31 > Subject: Re: [time-nuts] Predicting clock stability from > thevariouscharacterizationmethods > > Hi Tom: > > Is there a way to use the Allan plot to predict the variation in a reading? > For example if you use the plot comparing the 1 PPS from a GPS receiver to a > good Cesium frequency standard, then: > (1) what size of variation would you expect if the Cesium standard was > divided down to 1 kHz and that was compared to the GPS 1 PPS, or > (2) what size of variation would you expect if the Cesium standard was > divided down to 1 Pulse/1,000 seconds? > > Have Fun, > > Brooke Clarke > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > Tom Surely the time standard deviation should be: TDEV = TAU*MODADEV(TAU)/SQRT(3) ?? At least this appears to be so in the link you gave: http://www.wriley.com/paper2ht.htm Bruce