[time-nuts] GPS Antennas

[Bob kb8tq]

Hi

There are a lot of 3D printers out there that happily print ABS ….

Bob

> On Oct 15, 2019, at 10:17 AM, Attila Kinali <attila at kinali.ch> wrote:
> 
> 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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> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neal Stephenson
> 
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