[time-nuts] GPS Filter

Pieter ten Pierick time-nuts-mail at tenpierick.com
Tue Mar 8 12:24:12 UTC 2011


Hi,

> 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

But would such a system help with the LNA overload due to a local
transmitter?
I would expect that using separately steered antennas with good
directivity could prevent this out-of-band LNA overload?

Greetings,
Pieter.

>
> 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
>
>
>
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