GPS signals blocked by acrylic?
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GPS signals blocked by acrylic?

by Barry914 on Thu Feb 20, 2014 2:03 pm

I can't acquire or retain a GPS fix when the patch antenna on the Flora GPs is inside a clear acrylic box unless I take the lid off. Does that sound right?
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Re: GPS signals blocked by acrylic?

by 1chicagodave on Thu Feb 20, 2014 2:37 pm

Research done with Lexan has shown issues with signal transmission when the angle of incidence between the transmitting antenna and the Lexan material is greater than 30° from perdendicular. Since Acrylic has similar electrical properties to Lexan (dielectric constant, dielectric strength, dissipation factor, surface resistivity....), and since GPS works by having satellites at varying angles & distances from the receiver....it would make sense that an acrylic 'lid' over the GPS receiver could cause signal problems.
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Re: GPS signals blocked by acrylic?

by Barry914 on Thu Feb 20, 2014 2:49 pm

Thanks for that info. I see that glass appears to be pretty transparent to the signals. I just drilled a 3/4" hole in the top of the box and that seems to fix one problem, and I'm going to try putting a piece of microscope slide over the hole to see if that works too.
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Re: GPS signals blocked by acrylic?

by Barry914 on Thu Feb 20, 2014 4:03 pm

Looks like it's working fine with a glass window. I tried several different plastics to cover the hole in the lid and all gave me problems. I could lay a glass microscope slide right on the antenna without seeming to impact acquisition time (my proxy for measuring actual signal strength). It's hard to tell in the picture but the slide is glued to the inside of the cover.
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Re: GPS signals blocked by acrylic?

by 1chicagodave on Thu Feb 20, 2014 4:14 pm

Sweet! That was quick.

Nice case, too!
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Re: GPS signals blocked by acrylic?

by Barry914 on Mon Mar 03, 2014 3:40 pm

1chicagodave wrote:Nice case, too!


The case is made from two 2" x 3/4"boxes from the Container Store. They are bolted together bottom to bottom with the same screws that mount a USB charger in the bottom, which also holds the 500 mAh Li-Po battery and on-off switch. The top holds a Neo Geo Watch sandwich - NeoPixel ring, GPS, Flora, magnetometer, plus a push button. The battery also powers the GPS's VBackup pin. I've dubbed it my NeoGeo GoBack Machine because I can save a location and then use the device to find my way back.
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