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.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
