On Fri, 2 Aug 2002, Jim wrote:

>... simple test for transparency to RF at 1.575 GHz
>is to place the GPS antenna inside then outside the
>plastic box under consideration then (given the right
>module!) read the difference in signal stength (my JRC
>OEM modules in one mode do this trick with ease and
>the SS value measured is output relative in deciBels) ...
>
>Second test: Place the GPS antenna in the final position
>within the plastic box under consideration in the *same*
>proximity to the plastic box's top surface and again
>measure the signal strength.
>
>Proximity of the antenna to the platic "cover" will affect
>antenna pattern directly and therefore affect indirectly
>the antenna's utltimate gain in the desired direction.
>
>(I think I saw a previous post along the same lines but
>no reference to the box's plastic affecting the antenna
>pattern when in close proximity ...)

I'll make a blind guess about the change of angle of view due to the
dielectric plastic affecting the gain negligibly, for a point source at
infinity and an initial angle of view of >60 degrees. ;-)

However it could worsen the SWR by changing the impedance of some
elements. So get a box with a RF window (make a hole in almost any box).
You can buy spare radomes for satellite LNBs and make a hole in your box
to fit that. I hope your windshield does not have an antistatic layer.
Also no antireflex coating or oxide metalization (some toned windows) ;-)

Peter

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body