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