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To: arun gera who wrote (2393)	3/30/1998 2:23:00 PM
From: David	Respond to of 3506

New frequency, as interpreted for a lay audience by today's NY Times: "The change would not affect the performance of the best commercial G.P.S. receivers, which cost up to $30,000 and, using satellite signals, can pinpoint a location to within centimeters . . . . They are used by surveyors laying out property lines and by scientists studying small movements of land to predict earthquakes. "But the cheapest devices, the ones sold for $100 to $200, could establish a location to within 33 feet or less. Existing inexpensive units promise accuracy to within 325 feet, and generally provide accuracy to within about 115 to 160 feet. "'What this does for the common user, the guy who has the $199 receiver, is you're going to be able to get back to a fishing hole or whatever, not within 150 feet, but within 20 or 30 feet,' the White House official said, speaking on a condition of anonymity. "G.P.S. receivers in cars can signal their position to a central office, so that a driver who is lost can ask for directions without knowing the car's precise location. Existing technology allows a central dispatcher to know that the driver is on, for example, Interstate 95, but with the new system the dispatcher would know whether it was in the northbound or southbound lanes. . . . "G.P.S. receivers work by processing signals from three to eight satellites, but might gain the new accuracy if only one of those signals came from an improved satellite, the White House official said. " . . . The new plan calls for a system that can eliminate service in certain geographic areas as needed in the event of a war in an area. "A second source of error [besides Selective Availability] is distortion of the radio signals in the ionosphere . . . The improved system would compensate for that by sending signals on two radio frequencies. "Each frequency would be affected differently by the distortion, and the receiver on the ground would compare the signals, calculate the extent of the distortion, and correct for it."