[time-nuts] GPS Filter

[Bruce Griffiths]

GPS phased arrays aren't new, nor is it necessary to physically steer 
the antennae within the aray:
http://www.navsys.com/papers/0005004.pdf

Bruce

Magnus Danielson wrote:
> 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
>