Empathy List Archives

DJ

Dave Jabson

Fri, Nov 19, 2010 8:56 PM

Greetings,

I just discovered this mailing list, this is my first submission. Glad to
find a group of folks who are into this kind of stuff!

I'm working on an data acquisition application for my company that will
require a very stable oscillator. Without going into too many specifics,
there will be some reference stations spaced 100's of kilometers apart from
each other and 1 mobile station that will be operated in an area where GPS
is not available. I need to be able to collect data at all the stations and
have the time synchronization be extremely good between the stations,
including the one without GPS.

For the reference stations it will be sufficient to have the timing of each
one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA
string and 1pps edge and all of the digital electronics will use the GPSDO
10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be
done as needed.

The mobile station can be synchronized to GPS initially to synchronize its
clock as described above but will then have to rely on a free-running
oscillator. The stability of this oscillator will dictate how much drift the
mobile station's clock will experience relative to the reference stations.
Keeping this drift as low as possible is my goal.

I had assumed that a Rubidium oscillator would give me the best stability
over the course of 8-12 hours. Obviously a Cesium would be better but those
are impractical due to cost and power constraints. I've begun evaluation of
a Rb oscillator but now I'm being told by some people that a good DOCXO is
likely to give me similar medium term stability (with obviously better
short-term stability).

Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for
cost and power reasons if there's no performance benefit to be had using a
Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm)
seems to perform well but I am interested in hearing others' thoughts.

Thanks,

Dave

Dave Jabson
Systems Engineering Manager
Quasar Federal Systems
5754 Pacific Center Blvd, Suite 203
San Diego, CA 92121
858-412-1706
www.quasarfs.com

Greetings, I just discovered this mailing list, this is my first submission. Glad to find a group of folks who are into this kind of stuff! I'm working on an data acquisition application for my company that will require a very stable oscillator. Without going into too many specifics, there will be some reference stations spaced 100's of kilometers apart from each other and 1 mobile station that will be operated in an area where GPS is not available. I need to be able to collect data at all the stations and have the time synchronization be extremely good between the stations, including the one without GPS. For the reference stations it will be sufficient to have the timing of each one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA string and 1pps edge and all of the digital electronics will use the GPSDO 10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be done as needed. The mobile station can be synchronized to GPS initially to synchronize its clock as described above but will then have to rely on a free-running oscillator. The stability of this oscillator will dictate how much drift the mobile station's clock will experience relative to the reference stations. Keeping this drift as low as possible is my goal. I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for cost and power reasons if there's no performance benefit to be had using a Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) seems to perform well but I am interested in hearing others' thoughts. Thanks, Dave ---------------------- Dave Jabson Systems Engineering Manager Quasar Federal Systems 5754 Pacific Center Blvd, Suite 203 San Diego, CA 92121 858-412-1706 www.quasarfs.com

W

WB6BNQ

Fri, Nov 19, 2010 9:17 PM

Dave,

Something is not making sense to me here. As GPS is generally available around
the globe and obviously to your reference stations; how is it that the mobile
will be able to find an area where the GPS is not available ?

As to the mobile, if it is not going to utilize the GPS for a reference, you then
need to determine the worst case error you can have over the course of time that
the mobile is away from its GPS capability. That factor will dictate the kind of
on-board reference you will need. It could be that a very good quality crystal
oscillator will suffice.

Bill....WB6BNQ

Dave Jabson wrote:

Greetings,

I just discovered this mailing list, this is my first submission. Glad to
find a group of folks who are into this kind of stuff!

I'm working on an data acquisition application for my company that will
require a very stable oscillator. Without going into too many specifics,
there will be some reference stations spaced 100's of kilometers apart from
each other and 1 mobile station that will be operated in an area where GPS
is not available. I need to be able to collect data at all the stations and
have the time synchronization be extremely good between the stations,
including the one without GPS.

For the reference stations it will be sufficient to have the timing of each
one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA
string and 1pps edge and all of the digital electronics will use the GPSDO
10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be
done as needed.

The mobile station can be synchronized to GPS initially to synchronize its
clock as described above but will then have to rely on a free-running
oscillator. The stability of this oscillator will dictate how much drift the
mobile station's clock will experience relative to the reference stations.
Keeping this drift as low as possible is my goal.

I had assumed that a Rubidium oscillator would give me the best stability
over the course of 8-12 hours. Obviously a Cesium would be better but those
are impractical due to cost and power constraints. I've begun evaluation of
a Rb oscillator but now I'm being told by some people that a good DOCXO is
likely to give me similar medium term stability (with obviously better
short-term stability).

Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for
cost and power reasons if there's no performance benefit to be had using a
Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm)
seems to perform well but I am interested in hearing others' thoughts.

Thanks,

Dave

Dave Jabson
Systems Engineering Manager
Quasar Federal Systems
5754 Pacific Center Blvd, Suite 203
San Diego, CA 92121
858-412-1706
www.quasarfs.com

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Dave, Something is not making sense to me here. As GPS is generally available around the globe and obviously to your reference stations; how is it that the mobile will be able to find an area where the GPS is not available ? As to the mobile, if it is not going to utilize the GPS for a reference, you then need to determine the worst case error you can have over the course of time that the mobile is away from its GPS capability. That factor will dictate the kind of on-board reference you will need. It could be that a very good quality crystal oscillator will suffice. Bill....WB6BNQ Dave Jabson wrote: > Greetings, > > I just discovered this mailing list, this is my first submission. Glad to > find a group of folks who are into this kind of stuff! > > I'm working on an data acquisition application for my company that will > require a very stable oscillator. Without going into too many specifics, > there will be some reference stations spaced 100's of kilometers apart from > each other and 1 mobile station that will be operated in an area where GPS > is not available. I need to be able to collect data at all the stations and > have the time synchronization be extremely good between the stations, > including the one without GPS. > > For the reference stations it will be sufficient to have the timing of each > one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA > string and 1pps edge and all of the digital electronics will use the GPSDO > 10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be > done as needed. > > The mobile station can be synchronized to GPS initially to synchronize its > clock as described above but will then have to rely on a free-running > oscillator. The stability of this oscillator will dictate how much drift the > mobile station's clock will experience relative to the reference stations. > Keeping this drift as low as possible is my goal. > > I had assumed that a Rubidium oscillator would give me the best stability > over the course of 8-12 hours. Obviously a Cesium would be better but those > are impractical due to cost and power constraints. I've begun evaluation of > a Rb oscillator but now I'm being told by some people that a good DOCXO is > likely to give me similar medium term stability (with obviously better > short-term stability). > > Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for > cost and power reasons if there's no performance benefit to be had using a > Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) > seems to perform well but I am interested in hearing others' thoughts. > > Thanks, > > Dave > > ---------------------- > > Dave Jabson > Systems Engineering Manager > Quasar Federal Systems > 5754 Pacific Center Blvd, Suite 203 > San Diego, CA 92121 > 858-412-1706 > www.quasarfs.com > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

J

jimlux

Fri, Nov 19, 2010 9:30 PM

WB6BNQ wrote:

Dave,

Something is not making sense to me here. As GPS is generally available around
the globe and obviously to your reference stations; how is it that the mobile
will be able to find an area where the GPS is not available ?

If GPS is jammed, you're in a high multipath area, or other reasons...
Maybe the reference stations are above water, but your mobile unit is
underwater during most of the data collection. Or if you're doing
underground surveying.. not necesarily well logging, but say you're
doing Electromagnetic surveys,

I can think of lots of scenarios needing this..

As to the mobile, if it is not going to utilize the GPS for a reference, you then
need to determine the worst case error you can have over the course of time that
the mobile is away from its GPS capability. That factor will dictate the kind of
on-board reference you will need. It could be that a very good quality crystal
oscillator will suffice.

Indeed.. if you're looking at times <24hrs, a good OCXO would probably
do it.

I'm working on an data acquisition application for my company that will
require a very stable oscillator. Without going into too many specifics,
there will be some reference stations spaced 100's of kilometers apart from
each other and 1 mobile station that will be operated in an area where GPS
is not available. I need to be able to collect data at all the stations and
have the time synchronization be extremely good between the stations,
including the one without GPS.

For the reference stations it will be sufficient

Sufficient meaning you need tens of nanoseconds sort of precision/accuracy?

The mobile station can be synchronized to GPS initially to synchronize its
clock as described above but will then have to rely on a free-running
oscillator. The stability of this oscillator will dictate how much drift the
mobile station's clock will experience relative to the reference stations.
Keeping this drift as low as possible is my goal.

How good does it have to be, and how long will you be "out of touch"...

"as low as possible" is pretty darn low in this crowd.. Do you need 1
part in 1E13 over a week?

Or 1 ppb over a day? (about 100 microseconds/day)

Are you recording RF/Acoustic signals and need to be able to form
coherent sums?

I had assumed that a Rubidium oscillator would give me the best stability
over the course of 8-12 hours. Obviously a Cesium would be better but those
are impractical due to cost and power constraints. I've begun evaluation of
a Rb oscillator but now I'm being told by some people that a good DOCXO is
likely to give me similar medium term stability (with obviously better
short-term stability).

Almost certainly... the advantage of an Rb is that you can turn it off,
then turn it back on days later, and in a relatively short time, have
decent absolute accuracy.

WB6BNQ wrote: > Dave, > > Something is not making sense to me here. As GPS is generally available around > the globe and obviously to your reference stations; how is it that the mobile > will be able to find an area where the GPS is not available ? If GPS is jammed, you're in a high multipath area, or other reasons... Maybe the reference stations are above water, but your mobile unit is underwater during most of the data collection. Or if you're doing underground surveying.. not necesarily well logging, but say you're doing Electromagnetic surveys, I can think of lots of scenarios needing this.. > > As to the mobile, if it is not going to utilize the GPS for a reference, you then > need to determine the worst case error you can have over the course of time that > the mobile is away from its GPS capability. That factor will dictate the kind of > on-board reference you will need. It could be that a very good quality crystal > oscillator will suffice. Indeed.. if you're looking at times <24hrs, a good OCXO would probably do it. > >> >> I'm working on an data acquisition application for my company that will >> require a very stable oscillator. Without going into too many specifics, >> there will be some reference stations spaced 100's of kilometers apart from >> each other and 1 mobile station that will be operated in an area where GPS >> is not available. I need to be able to collect data at all the stations and >> have the time synchronization be extremely good between the stations, >> including the one without GPS. >> >> For the reference stations it will be sufficient Sufficient meaning you need tens of nanoseconds sort of precision/accuracy? >> The mobile station can be synchronized to GPS initially to synchronize its >> clock as described above but will then have to rely on a free-running >> oscillator. The stability of this oscillator will dictate how much drift the >> mobile station's clock will experience relative to the reference stations. >> Keeping this drift as low as possible is my goal. How good does it have to be, and how long will you be "out of touch"... "as low as possible" is pretty darn low in this crowd.. Do you need 1 part in 1E13 over a week? Or 1 ppb over a day? (about 100 microseconds/day) Are you recording RF/Acoustic signals and need to be able to form coherent sums? >> >> I had assumed that a Rubidium oscillator would give me the best stability >> over the course of 8-12 hours. Obviously a Cesium would be better but those >> are impractical due to cost and power constraints. I've begun evaluation of >> a Rb oscillator but now I'm being told by some people that a good DOCXO is >> likely to give me similar medium term stability (with obviously better >> short-term stability). Almost certainly... the advantage of an Rb is that you can turn it off, then turn it back on days later, and in a relatively short time, have decent absolute accuracy. >>

BC

Bob Camp

Fri, Nov 19, 2010 10:41 PM

Hi

How much "warmup" time do you have before you go mobile?

If the mobile unit can be kept hot before it heads out - the DOCXO wins. If it's a "power up and roll in 10 minutes" sort of thing, then the Rb is the only way to go.

Bob

On Nov 19, 2010, at 3:56 PM, Dave Jabson wrote:

Greetings,

I just discovered this mailing list, this is my first submission. Glad to
find a group of folks who are into this kind of stuff!

I'm working on an data acquisition application for my company that will
require a very stable oscillator. Without going into too many specifics,
there will be some reference stations spaced 100's of kilometers apart from
each other and 1 mobile station that will be operated in an area where GPS
is not available. I need to be able to collect data at all the stations and
have the time synchronization be extremely good between the stations,
including the one without GPS.

For the reference stations it will be sufficient to have the timing of each
one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA
string and 1pps edge and all of the digital electronics will use the GPSDO
10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be
done as needed.

The mobile station can be synchronized to GPS initially to synchronize its
clock as described above but will then have to rely on a free-running
oscillator. The stability of this oscillator will dictate how much drift the
mobile station's clock will experience relative to the reference stations.
Keeping this drift as low as possible is my goal.

I had assumed that a Rubidium oscillator would give me the best stability
over the course of 8-12 hours. Obviously a Cesium would be better but those
are impractical due to cost and power constraints. I've begun evaluation of
a Rb oscillator but now I'm being told by some people that a good DOCXO is
likely to give me similar medium term stability (with obviously better
short-term stability).

Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for
cost and power reasons if there's no performance benefit to be had using a
Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm)
seems to perform well but I am interested in hearing others' thoughts.

Thanks,

Dave

Dave Jabson
Systems Engineering Manager
Quasar Federal Systems
5754 Pacific Center Blvd, Suite 203
San Diego, CA 92121
858-412-1706
www.quasarfs.com

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi How much "warmup" time do you have before you go mobile? If the mobile unit can be kept hot before it heads out - the DOCXO wins. If it's a "power up and roll in 10 minutes" sort of thing, then the Rb is the only way to go. Bob On Nov 19, 2010, at 3:56 PM, Dave Jabson wrote: > Greetings, > > I just discovered this mailing list, this is my first submission. Glad to > find a group of folks who are into this kind of stuff! > > I'm working on an data acquisition application for my company that will > require a very stable oscillator. Without going into too many specifics, > there will be some reference stations spaced 100's of kilometers apart from > each other and 1 mobile station that will be operated in an area where GPS > is not available. I need to be able to collect data at all the stations and > have the time synchronization be extremely good between the stations, > including the one without GPS. > > For the reference stations it will be sufficient to have the timing of each > one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA > string and 1pps edge and all of the digital electronics will use the GPSDO > 10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be > done as needed. > > The mobile station can be synchronized to GPS initially to synchronize its > clock as described above but will then have to rely on a free-running > oscillator. The stability of this oscillator will dictate how much drift the > mobile station's clock will experience relative to the reference stations. > Keeping this drift as low as possible is my goal. > > I had assumed that a Rubidium oscillator would give me the best stability > over the course of 8-12 hours. Obviously a Cesium would be better but those > are impractical due to cost and power constraints. I've begun evaluation of > a Rb oscillator but now I'm being told by some people that a good DOCXO is > likely to give me similar medium term stability (with obviously better > short-term stability). > > Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for > cost and power reasons if there's no performance benefit to be had using a > Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) > seems to perform well but I am interested in hearing others' thoughts. > > Thanks, > > Dave > > ---------------------- > > Dave Jabson > Systems Engineering Manager > Quasar Federal Systems > 5754 Pacific Center Blvd, Suite 203 > San Diego, CA 92121 > 858-412-1706 > www.quasarfs.com > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

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DOCXO vs. Rubidium medium-term stability