[time-nuts] GPS ceramic patch in what plastic housing?

[jimlux]

Predrag Dukic wrote:
> 
> Bill,
> 
> Pyrex ( and any other glass) could reflect too much. It is true that glass,
> 
> depending on composition, is not absorbing microwaves, and does not heat 
> itself in the owen,
> 
> but how much it is transparent at 2.4 ghz should be checked somehow...
> 
> P. Dukic
> 
> 
>

I wouldn't use a glass jar/mixing bowl, what-have-you.

A) glass is a bit lossy  (even at 100-200kHz), but probably not enough 
to be an issue.. (Now, if you were building kW scale capacitors for a 
tesla coil, that's a different thing)

B) A bigger problem: Glass has a (unevenly controlled) dielectric 
constant of around 2.5..

So, you'll get reflections at both interfaces as well as some refraction 
as the signal passes through the "radome"

The whole radome design thing is much trickier than one might think for 
a something where angle of incidence is important.  There's a reason 
that you see lots of hemispheres, and one tries to control the thickness 
of the radome (in fact, sometimes, you make the shell from a honeycomb 
core with 2 face sheets, although at L band, this would be tricky).

So, either you use something simple, and accept whatever defects it 
creates in your antenna pattern, or get fancy.

Glass babyfood or canning jars will probably work, and will literally 
last your life time. White painted plastic would also work.

  Watch out for things like appropriately venting it (so moisture 
doesn't collect inside) and making sure it doesn't make a little solar 
oven (gotta paint that clear glass, I suspect)