[time-nuts] Better GPS

WarrenS warrensjmail-one at yahoo.com
Fri Aug 27 17:44:50 UTC 2010


Thanks Bob, Interesting stuff.

>Has anybody else dug into any of this?
I have no experience with using LI/L2, or how good it is,
But as far as making Tbolt's better, No problem to make them > "2 or 3X" 
better all the time, by going to an external better optimized controller 
algorithm.
Lady Heather has a simple external PID controller built in that shows proof 
of concept.
Much better could be done with the Tbolt if there is a need, using a simple 
PIC micro and add that into something like the Tbolt monitor.

ws

**************
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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