[time-nuts] Rubidium (Rb) or Caesium (Cs)

Jim Lux jimlux at earthlink.net
Tue Oct 18 20:13:48 EDT 2011


On 10/18/11 3:32 PM, Tom Van Baak wrote:

> ** Choke ring, ground plane -- this has been covered before.
> Along with temperature stabilized antenna, cables, and/or
> receiver, it's an inexpensive way to gain some performance.
> I don't have numbers but it seems at the point people use
> dual-frequency and carrier-phase receivers they start to
> pay this level of attention to the antenna.

My GPS buddies here at JPL say that there's a whole raft of effects that 
one needs to start taking into account when you get to 1 meter/3ns kinds 
of precision. Apparently, for a variety of practical reasons, things are 
built so that no one error source dominates in a particular accuracy 
class.  (e.g. if you're figuring out how to find the nearest In-n-Out 
Burger, you probably don't need a choke ring antenna). Solid earth 
tides, ionosphere, etc.,etc.etc.

>
> ** Post-processing -- there is a penalty for knowing what
> time you think it is right now vs. knowing what time it really
> was an hour or day ago. Most high-end navigation/timing
> systems separate data collection from precise results. If
> over time you can combine the results of tens of hundreds
> of other labs everyone can benefit from greater accuracy.
> When you get below a nanosecond, precise orbits and
> signal propagation are very complicated and variable.

GIPSY is offered to all comers, for free.  All you need is the ability 
to generate RINEX format files.

http://apps.gdgps.net/

http://www.gdgps.net/

You can do (I understand, not having tried it) things like post process 
your data to compensate for ionospheric effects (measured by others)




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