Re: [time-nuts] GPS through windows
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.
Re: [time-nuts] GPS through windows
The low-E coatings are known to attenuate WIFI. WIFI is probably a worse case than GPS, but the availability of the gear makes experimenting easy. I think they are sputtered metal either on the glass or on a thin film applied to the glass. Southwall Technology in Palo Alto pioneered or at least commercialized the technology. Pay-walls on technical journals have to go. The IEEE doesn't pay the author for the article. They used to make the author pay a small fee. Anyway, the exorbitant fees of technical journals discourages cross-discipline research. You can't be a member of every one of these societies. The US government papers (Department of Energy for instance) are free on the DOE websites, but under a paywall on other government websites. (AKA left hand not talking to the right hand.) End of soap-box rant. ___ 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.
Re: [time-nuts] GPS through windows
On Mon, Jun 4, 2012 at 11:26 PM, li...@lazygranch.com wrote: The low-E coatings are known to attenuate WIFI. WIFI is probably a worse case than GPS, but the availability of the gear makes experimenting easy. I think they are sputtered metal either on the glass or on a thin film applied to the glass. Southwall Technology in Palo Alto pioneered or at least commercialized the technology. They are interference filters. Layered coating 1/4 wavelength thick that send some waves back in phase and other out of phase, they reflect heat and UV be let light go through. I think it is a tin oxide coating of some kind. Sometime they use silver but only on the inside of a double pane window with the inside filled with inert gas, otherwise the silver tarnishes. OK, I think they can also over coat the silver with an oxide to keep the air away from it I think my windows at home have both. I can see the 1/4 wave coating change color with the angle I look at the glass, the silver simply darkens the glass. The argon gas between the panes is for insulation. I assume it is the metallic silver coat the messes with RF signals. I think the silver is very common in large buildings. But with a large building they make the glass custom to the architect's specifications so no one can know what is in your building. Chris Albertson Redondo Beach, California ___ 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.
Re: [time-nuts] GPS through windows
On 6/5/12 9:14 AM, Chris Albertson wrote: On Mon, Jun 4, 2012 at 11:26 PM,li...@lazygranch.com wrote: The low-E coatings are known to attenuate WIFI. WIFI is probably a worse case than GPS, but the availability of the gear makes experimenting easy. I think they are sputtered metal either on the glass or on a thin film applied to the glass. Southwall Technology in Palo Alto pioneered or at least commercialized the technology. They are interference filters. Layered coating 1/4 wavelength thick that send some waves back in phase and other out of phase, they reflect heat and UV be let light go through. I think it is a tin oxide coating of some kind. or Indium Tin Oxide (ITO) which is transparent and conductive. Sometime they use silver but only on the inside of a double pane window with the inside filled with inert gas, otherwise the silver tarnishes. OK, I think they can also over coat the silver with an oxide to keep the air away from it yes.. the german young lady was working with triple pane windows filled with Argon I think my windows at home have both. I can see the 1/4 wave coating change color with the angle I look at the glass, the silver simply darkens the glass. The argon gas between the panes is for insulation. I assume it is the metallic silver coat the messes with RF signals. I think the silver is very common in large buildings. But with a large building they make the glass custom to the architect's specifications so no one can know what is in your building. Chris Albertson Redondo Beach, California ___ 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. ___ 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.
Re: [time-nuts] GPS through windows
Part of the problem of using a window would remain even if the glass where removed. This is the antenna can not see the entire sky from a window. You can do ok if the window faces South (assume you are in the Northern Hemisphere) With a good timing GPS receiver you only need to see a very small number of satellites. So the window can work but you would get better results if you can see the horizon all 360 degrees around. Is there no access to the roof? What about the roof of some other building. Place the antenna and the receiver on the roof and send the data back via some kind of link. Using a higher gain antenna might (make up for any attenuation cause be coating on the glass. So it might work. On Mon, Jun 4, 2012 at 10:24 PM, Hal Murray hmur...@megapathdsl.net 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? -- 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. -- These are my opinions. I hate spam. ___ 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. -- Chris Albertson Redondo Beach, California ___ 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.
