[time-nuts] Rooftop antenna and splitter

[Attila Kinali]

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