Better GPS
Hi
I've been digging around at acc.igs.org. They seem to think that their clock models are good to below 0.05 ns. They compare that to a 2 ns number for the "as broadcast" models. 2 ns is a pretty familiar number if you look at a lot of TBolt plots. All of their data is online and available for download at some point in time past live. The longer you wait the better the data.
They really like the idea of L1/L2 receivers and fancy post processing. They also are after a lot more than just time. I still have not noticed any complete L1/L2 receivers for < $100, so I can't do their full solution approach. Ionospheric correction seems to be one big thing you loose by going single freq.
There's a pretty good summary of all that at http://acc.igs.org/UsingIGSProductsVer21.pdf
Since the TBolt sort but not quite of does carrier phase you might be able to use their data to improve things. I doubt that you would get to 50 ps, but even a 2 or 3X improvement would be worthwhile. Even getting it some of the time (midnight?) would still be useful. It would be a log lots of data and compare thing - not that unusual.
Has anybody else dug into any of this?
Is there a secret stash of cheap L1/L2 fixed location receivers out there that I haven't stumbled across?
Can you really win the lottery by picking up the winning ticket off the sidewalk?
Lots of questions....
Bob
Hi Bob:
The ultimate is a carrier phase GPS Timing receiver. The early work was
done using Ashtech Z12 models that have a provision for an external 10
MHz oscillator. I have a feeling that the units you're talking about
are a refinement of this approach.
The new L5 frequency of GPS, intended for FAA use, will allow for
civilian two frequency ionosphere corrections in a more straight forward
way than the existing methods (squaring, Ashtech) of using L2 without
knowing the P(Y) crypto keys.
http://www.prc68.com/I/DAGR.shtml#GPSs
Have Fun,
Brooke Clarke
http://www.PRC68.com
Bob Camp wrote:
Hi
I've been digging around at acc.igs.org. They seem to think that their clock models are good to below 0.05 ns. They compare that to a 2 ns number for the "as broadcast" models. 2 ns is a pretty familiar number if you look at a lot of TBolt plots. All of their data is online and available for download at some point in time past live. The longer you wait the better the data.
They really like the idea of L1/L2 receivers and fancy post processing. They also are after a lot more than just time. I still have not noticed any complete L1/L2 receivers for< $100, so I can't do their full solution approach. Ionospheric correction seems to be one big thing you loose by going single freq.
There's a pretty good summary of all that at http://acc.igs.org/UsingIGSProductsVer21.pdf
Since the TBolt sort but not quite of does carrier phase you might be able to use their data to improve things. I doubt that you would get to 50 ps, but even a 2 or 3X improvement would be worthwhile. Even getting it some of the time (midnight?) would still be useful. It would be a log lots of data and compare thing - not that unusual.
Has anybody else dug into any of this?
Is there a secret stash of cheap L1/L2 fixed location receivers out there that I haven't stumbled across?
Can you really win the lottery by picking up the winning ticket off the sidewalk?
Lots of questions....
Bob
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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--
Have Fun,
Brooke Clarke
http://www.PRC68.com
Hi Bob:
Here's an interesting sidebar:
Precision Modeling for Orbit Determination
http://www.aero.org/publications/crosslink/summer2002/02_sidebar2.html
from the web page:
Orbit Determination and Satellite Navigation
http://www.aero.org/publications/crosslink/summer2002/04.html
I didn't know the Moon tides can change the elevation of LA by 40 cm!
Have Fun,
Brooke Clarke
http://www.PRC68.com
Bob Camp wrote:
Hi
I've been digging around at acc.igs.org. They seem to think that their clock models are good to below 0.05 ns. They compare that to a 2 ns number for the "as broadcast" models. 2 ns is a pretty familiar number if you look at a lot of TBolt plots. All of their data is online and available for download at some point in time past live. The longer you wait the better the data.
They really like the idea of L1/L2 receivers and fancy post processing. They also are after a lot more than just time. I still have not noticed any complete L1/L2 receivers for< $100, so I can't do their full solution approach. Ionospheric correction seems to be one big thing you loose by going single freq.
There's a pretty good summary of all that at http://acc.igs.org/UsingIGSProductsVer21.pdf
Since the TBolt sort but not quite of does carrier phase you might be able to use their data to improve things. I doubt that you would get to 50 ps, but even a 2 or 3X improvement would be worthwhile. Even getting it some of the time (midnight?) would still be useful. It would be a log lots of data and compare thing - not that unusual.
Has anybody else dug into any of this?
Is there a secret stash of cheap L1/L2 fixed location receivers out there that I haven't stumbled across?
Can you really win the lottery by picking up the winning ticket off the sidewalk?
Lots of questions....
Bob
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.
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
Brooke Clarke wrote:
Hi Bob:
Here's an interesting sidebar:
Precision Modeling for Orbit Determination
http://www.aero.org/publications/crosslink/summer2002/02_sidebar2.html
from the web page:
Orbit Determination and Satellite Navigation
http://www.aero.org/publications/crosslink/summer2002/04.html
I didn't know the Moon tides can change the elevation of LA by 40 cm!
oh yeah... all my GPS/geodetic friends at work say that once you get
down into the "sub-meter" range for gps (or sub 3 ns..same thing)
there's a whole raft of errors in that ballpark.. tidal displacement,
ionosphere, multipath, atmospheric refraction, etc.
They say it's sort of a "whack-a-mole" when you're trying to get better
than that (for non-differential measurements)
You'd think that something at the edge of a continent that moved
up and down that much every month would break off.
Wait, it's rock all the way down.
Bill Hawkins
-----Original Message-----
From: Brooke Clarke
Sent: Friday, August 27, 2010 12:34 PM
---snip---
I didn't know the Moon tides can change the elevation of LA by 40 cm!
On 08/27/2010 07:03 PM, Brooke Clarke wrote:
Hi Bob:
The ultimate is a carrier phase GPS Timing receiver. The early work was
done using Ashtech Z12 models that have a provision for an external 10
MHz oscillator. I have a feeling that the units you're talking about are
a refinement of this approach.
The new L5 frequency of GPS, intended for FAA use, will allow for
civilian two frequency ionosphere corrections in a more straight forward
way than the existing methods (squaring, Ashtech) of using L2 without
knowing the P(Y) crypto keys.
http://www.prc68.com/I/DAGR.shtml#GPSs
The L2C alongside L1 C/A and L5 would allow three-frequency
observations. You would always benefit from doing P(Y) observations
along-side. A modern receiver would be able to make at least 5
observations from the most modern birds, 4 from many and just 3 from the
older birds.
Modern receivers may also support GLONASS so an additional 3
observations may be done.
Cheers,
Magnus
I thought it had broken off (San Andreas Fault) ...
Dave
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Bill Hawkins
Sent: 27 August 2010 20:59
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Better GPS
You'd think that something at the edge of a continent that moved up and down that much every month would break off.
...
Bill Hawkins
Hi,
Hi
I've been digging around at acc.igs.org. They seem to think that their
clock models are good to below 0.05 ns. They compare that to a 2 ns number
for the "as broadcast" models. 2 ns is a pretty familiar number if you
look at a lot of TBolt plots. All of their data is online and available
for download at some point in time past live. The longer you wait the
better the data.
You can get some improvement even in 'real-time' by using the ultra-radid
(predicted) data available over Internet.
http://igscb.jpl.nasa.gov/components/prods.html
They really like the idea of L1/L2 receivers and fancy post processing.
They also are after a lot more than just time. I still have not noticed
any complete L1/L2 receivers for < $100, so I can't do their full solution
approach. Ionospheric correction seems to be one big thing you loose by
going single freq.
Yes, but you would only need one dual freq receiver to estimate the Iono.
Or have real time access to one in the vincinity. Another way, would be to
use the models for Iono and Tropo errors that are available in real time.
One example is the SBAS (Waas, Egnos, Msas, etc) signals. They should get
you down below 2 meters. Perhaps there are online models for prediction of
Iono related radio communications that could be useful.
Beeing connected to Internet opens a whole lot of possible improvements
not available for the classic standalone GPS receiver.
There's a pretty good summary of all that at
http://acc.igs.org/UsingIGSProductsVer21.pdf
Since the TBolt sort but not quite of does carrier phase you might be able
to use their data to improve things. I doubt that you would get to 50 ps,
but even a 2 or 3X improvement would be worthwhile. Even getting it some
of the time (midnight?) would still be useful. It would be a log lots of
data and compare thing - not that unusual.
Has anybody else dug into any of this?
I think we should examine the Tbolt measurement capabilities a little
further. One experiment that would eliminate local clock errors would be
to compare two Tbolts sharing both antenna and the same oscillator.
This is one avenue of might be improvements of the already good Tbolt
GPSDO. Other paths as controlling the temperature and optimizing control
parameters are ofcause also interesting.
Is there a secret stash of cheap L1/L2 fixed location receivers out there
that I haven't stumbled across?
Check with local surveying outfits, or close by CORS stations they might
have old receivers collecting dust.
--
Björn