[time-nuts] GPS antenna in silicon/RTV encapsulation

Jim Lux jimlux at earthlink.net
Wed Apr 16 08:08:57 EDT 2014


On 4/15/14, 8:16 PM, nuts wrote:
> I don't use the surf board resin. I use
>> http://www.tapplastics.com/product/fiberglass/polyester_resins/tap_marine_vinyl_ester_resin/34
> I don't have specifics on what Tap sells, but vinyl ester resins have a
> dielectic coeficient around 4 and dissipation of at least 0.00x. The
> resin is actually better than the S-2 glass.I suppose I can ask who
> makes their resin, but I don't know if anyone at a store has that
> answer.
>

ah, but this is "time nuts" and we obsess about the 14th decimal point<grin>

It kind of depends on what you're looking for.  For instance, I don't 
recall what the big radome over the fancy Leica multiband artichoke 
antennas is like.  I think it's just plastic (some UV inhibited 
plastic), but it might have glass or nomex in it.

The one over the actual elements (inside the choke ring) is some fairly 
exotic filled plastic in a carefully designed shape to keep the phase 
center in the same place regardless of incidence angle.

1mm phase center shift is 0.005 wavelength (about 2 degrees) of carrier 
phase.  Over a 8 hour pass (4.3E13 cycles) that's in the 1 part in 1E15 
range.






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