[time-nuts] GPS antenna with direction orientation?

bg at lysator.liu.se bg at lysator.liu.se
Mon Apr 4 11:10:16 UTC 2011


> A couple of years ago I picked up a surplus Aeroantenna choke-ring GPS
> antenna that I think was intended for surveying use.  I finally got it
> installed today and noticed that it has an arrow on the bottom
> indicating that the antenna should be oriented with the arrow facing
> north.

Most surveying antennas intended for static use has an "North" arrow or
are implicitly supposed to aligh the "connector" towards north.

> I'm trying to figure out why an omnidirectional antenna should care
> about which way it is oriented.  The best I can figure is that perhaps
> it is for repeatability in surveying, so that any minor offset in the
> phase center would remain consistent when moving the antenna from site
> to site.
>
> Does anyone have a better answer?

You are right!

I have a few chokerings with different antenna elements than the one show
in the below url:

http://www.ngs.noaa.gov/cgi-bin/query_cal_antennas.prl?Model=AER&Antenna=AERAT2775_43

If you look at the numbers below

     2.3       -.6      88.3    (L1)
     -.2        .2      94.1    (L2)

They are the x,y and z phase center offsets for L1 an L2 respectively. For
this antenna.

The other numbers are corrections based on angle of arrival to the
antenna. Nothing is really fully symmetric if you look closely enough.

The antenna calibration data is used by postprocessing GNSS software
packages.

--

    Björn




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