[time-nuts] GPS through windows

[Jim Lux]

On 6/4/12 10:24 PM, Hal Murray wrote:
>
> Does window glass have significant attenuation at GPS L1?
>
> What if it's a big window on a modern green office building and has some sort
> of coating/content to reduce IR transmission?
>
> Google found an (expensive) paper from IEEE where the abstract said:
>    At average, about 30 dB attenuation is observed from 800 MHz to 6 GHz
> so I assume the answer is mostly "sure does".
>
> Does anybody have more info?  Is there a rule of thumb?  (maybe X dB, or X
> dB/inch)  Does it vary wildly from brand to brand of glass?


varies wildly..  I remember being at a conference in Santa Clara in 1993 
with a Trimble Scout (one of the very first handheld GPS units that was 
practical.. the Sony one ate batteries).  Inside the main indoor hall 
with all the skylights you couldn't get a fix at all.

And the LA Convention Center had a similar problem in the mid 90s, when 
cellphones were really getting popular.  You couldn't get a cell signal, 
and there were all these conspiracy theories that it was the convention 
center wanting people to pay for wireline phone at their booth.

by the way...

There was a fantastic project by a young woman from Ilmenau Germany at 
the International Science and Engineering Fair this year. She modified 
thermal insulating windows (with the metallic coating) by designing a 
pattern of slots in the coating which passed cell phone and WiFi 
frequencies, without markedly affecting the thermal properties. You 
can't arrange the slots any old way, or you get grating lobes (Young two 
slit experiment with a vengeance).

>
> ----------
>
> Context is that I took some low cost consumer GPS toys when I visited a
> friend who had recently moved into a new office building.  He's on the 4th
> floor, well above anything else on that side, so we had a clear view for half
> of the sky looking West or slightly North of West.
>
> We tried a SiRF III and a Sure demo board.  I had forgotten to update the
> Sure clock the night before so it was having a hard time getting off the
> ground.  We took everything outside where they locked up within a few
> minutes.  Back inside with the antennas on a window sill, both just barely
> worked some of the time.
>
> The glass below the sill was a different color, slightly less yellow.  We
> tried the lower (floor level) sill but didn't notice any difference.  That
> wasn't a serious test with numbers and error bars, but we probably would have
> noticed if it had suddenly started working much better.
>
>
>