[time-nuts] GPS Filter

[Magnus Danielson]

On 03/08/2011 05:22 AM, Hal Murray wrote:
>
>> 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.

You would need to have a DGPS input stream generated in order to 
compensate sat for sat. If you don't have a DGPS input to the GPS 
receiver you are fairly stuck with the shifts...

Cheers,
Magnus