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Cedar Rapids, Iowa | The FM radio in your car - lets say there is a local FM radio station that broadcasts from a tower a mile away from where you are. When you are that close to the tower, you can tune your radio to the channel above or below their center frequency and still hear the station. When you are 20 miles from that tower, you will still hear the radio station on their center channel, but not on the channels above and below it. When a signal is broadcast at a very high power relative to what you're listening for, it will walk over neighboring frequencies. This is why you never see two FM radio stations broadcasting from towers in the same area on frequencies that are right next to each other.
LightSquared is already broadcasting signal from their satellite in the L Band. That isn't causing any issue because it at a similar power level to what the GPS signals are. However, when broadcasting their data from terrestrial towers, that signal is a billion times louder than what GPS is. The different power levels in close frequency proximity are the problem.
FM radio and TV stations often broadcast in excess of 100,000 watts output. LightSquared is only planning to push 1,400 watts. GPS receivers are able to filter out FM radio and TV because those frequencies are well outside the GPS realm. LightSquared is right next to GPS. | |
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LightSquared / GPS problem in a nutshell
