I learned this, and more, from an amazing comment by a guy named Michael replying to David Pogue's NY Times blog entry about disappointing reception on his iPhone's AT&T network. Michael's offering appears on page four of the comments...but I'll paste in the best stuff below (love the part about the buses). Geeks will enjoy the following soulfood:
"Cell phone signal strength is tested, but I don’t know how the results are used. Nor do I know who tests the carriers’ networks - the carriers or a contract company.
"One way that network strength is tested is in the back of Greyhound buses, on a fairly continual basis. I don’t know much more than that, except the test guy and his recording equipment gets the rear seat. This method tests signals along major USA corridors - like Interstate highways.
"DJH’s comment is correct - some carriers oversubscribe their networks. This was true of Sprint in 2000 in major metropolitan areas. You had a minute or two to discuss the core of your message before being dropped. [ Comcast was noteworthy for this same practice around the same time for Internet/TV subscriptions. ]
"Another issue that appears to have been changed between the iPhone 2.5G and 3G is the chrome decoration on the case. It’s a very good Faraday cage (signal hindrance), as is your car, and most buildings (with metal lathe, steel roofs, steel ductwork, metal skins, and energy efficient [metallized] windows. These conductive paths present a barrier to RF signals, as well as producing an echo chamber effect.
"The 3G iPhone seems to have removed much of the chrome decoration that acted as a Faraday cage. Unfortunately, the cell phone antennas are located at the bottom of the phone, right where most people hold them. People are conductive, and make pretty good Faraday cages. Interestingly enough, some people are more conductive than others. Maybe David Pogue’s electrolytes are stronger than other cell phone users? :-)"
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