[time-nuts] Rooftop antenna and splitter
Bob kb8tq
kb8tq at n1k.org
Wed Jan 30 23:19:11 UTC 2019
Hi
Indeed, putting a ground plane on a GPS antenna that is not designed
to use one will make it perform worse than it will with one. If the antenna
is a modern one that is designed for mounting on a tripod or a pole, it’s
a good bet it was designed to not have a ground plane backing it up.
A magnetic puck antenna that goes on a car - sure, it wants a ground
plane. It’s also a pretty sort term answer for a outdoor antenna…..
One thing that the newer receivers are going to want is a stable antenna
mount as well as a stable phase center. Since you now have L1 / L2 data,
you can properly process things to get (claimed) mm level accuracy on the
location. That is *way* better than you will get out of a normal “survey in”
sort of approach. It’s also free ….
Off to figure out how to get the F9P data into RINEX ….
Bob
> On Jan 30, 2019, at 5:29 PM, Attila Kinali <attila at kinali.ch> wrote:
>
> On Tue, 29 Jan 2019 21:29:20 +0100
> Achim Gratz <Stromeko at nexgo.de> wrote:
>
>> Typically if they already have a ground plane mounted it's between
>> 6cm…10cm in diameter (or side length if quadratic). Over that size you
>> shouldn't see much effect anymore on the antenna sensitivity pattern,
>
> There is quite a big difference in radiation patterns depending on
> the size of the ground plane. The back lobes but also the low-elevation
> sidelobes change quite dramatically when going from 10cm to 20cm to 1m.
> And even with the 1m antenna, having a sharp edge vs a serrated or
> curved edge makes again quite a bit of difference for back lobes.
>
> On Wed, 30 Jan 2019 20:41:26 +0100
> Achim Gratz <Stromeko at nexgo.de> wrote:
>
>> Use a resonant ground plane with four or eight tuned radials instead,
>> that also has the advantage of way lower wind load…
>
> Tuned elements with high Q are definitely not what you want with a
> GNSS antenna used for precision applications, as they cause large
> changes in group delay. Keep in mind that the GNSS signal has +/-6kHz
> of Doppler frequency.
>
> Also, having a non-planar ground plane will cause the phase centre
> to shift depending on the azimuth where the satellite is seen.
> Again something you do not want with precision applications.
>
>
> Attila Kinali
>
> --
> Science is made up of so many things that appear obvious
> after they are explained. -- Pardot Kynes
>
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