[time-nuts] GPS Filter

[Hal Murray]

> Since you are after timing off of the sat's, having antennas that move,
> either physically or electrically seems like a problem. Any shift in the
> effective antenna location as you tracked the satellite would be "exciting"
> to compensate for. There was an early paper published based on doing this
> (early 80's).  

You can correct for the antenna orientation.  (That's what software is for. 
:)  Radio astronomers have been doing it forever.

I think it's simple, at least in the nice/common cases.  If the antenna 
geometry has a point that everything swivels around, consider that to the the 
location of the antenna.  I think that covers the typical alt-az mount:
  http://en.wikipedia.org/wiki/Altazimuth_mount
The point is where those two axes intersect.  Now just fudge the coax delay 
to correct for the time/distance from the real antenna location to that 
point.  That's the before location coax delay (in there with the ionospheric 
delay) rather than the post GPS antenna-to-box delay.

Of course, it gets a bit more complicated than that if you want to track 
several satellites in real time.  That probably takes an antenna per 
satelite.  But again, VLBI  geeks have been doing that sort of math for ages.




-- 
These are my opinions, not necessarily my employer's.  I hate spam.