[time-nuts] GPS antenna with direction orientation?

Magnus Danielson magnus at rubidium.dyndns.org
Mon Apr 4 17:44:23 UTC 2011


On 04/04/2011 02:42 AM, John Ackermann N8UR wrote:
> 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.
>
> 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?

Since the phase-center is not completely stable with relation to 
direction, the antennas needs to be oriented in such a fashion that the 
corrections can be applied. It's routinely used in precision 
measurements such as the various reference networks.

The calibration files exists for known antennas, so then identifying the 
antenna would allow for the correct calibration file to be used.
So it boils down to turning the antenna so the arrow points north.

Cheers,
Magnus



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