[time-nuts] GPS Antennas

[Attila Kinali]

On Fri, 6 Sep 2019 10:07:29 -0700
Nick Sayer via time-nuts <time-nuts at lists.febo.com> wrote:

> I’m late to the party, but my go-to antenna is the Gilsson marine antenna. If 
> it has a downside, it’s that it has a flat top instead of a cone. I’ve got 
> one mounted outside at our vacation home near Lake Tahoe, so we’ll see 
> whether snow loading becomes a problem shortly. The fix would presumably just 
> be a 3D printed plastic gnome’s cap, though even that might not be useful if 
> we get snow like we did last year.

I don't recommend 3D printing. The materials used for 3D printing
are quite hygrophile, ie suck up a lot of humidity. This will give
you varations in the refraction index of the cover depending on
the air humidity.

Instead use some thin plastic sheet and thermoform it.
ABS is a good candidate for ease of thermoforming, with reasonable
RF performance. PTFE would be better (almost ideal) in terms of
RF performance, but is quite a bit more difficult to thermoform.
Though, considering how cheap PTFE sheets are, I would probably
try it anyways.

BTW: an indication of what the cover does on the phase center
can be found in [1]

			Attila Kinali

[1] "The Effect of Antenna Covers On GPS Baseline Solutions",
by Braun, Stephens, Ruud, Meertens, 1997
https://kb.unavco.org/kb/article.php?id=185

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