"common misconception" begone ... + + + + + + + + + + + + + + + + GPS CAPABILITIES < snip > GPS provides two levels of service, Standard Positioning Service and the Precise Positioning Service . The Standard Positioning Service (SPS) is a positioning and timing service which will be available to all GPS users on a continuous, worldwide basis with no direct charge. SPS will be provided on the GPS L1 frequency which contains a coarse acquisition (C/A) code and a navigation data message. SPS provides a predictable positioning accuracy of 100 meters (95 percent) horizontally and 156 meters (95 percent) vertically and time transfer accuracy to UTC within 340 nanoseconds (95 percent). The Precise Positioning Service (PPS) is a highly accurate military positioning, velocity and timing service which will be available on a continuous, worldwide basis to users authorized by the U.S. P(Y) code capable military user equipment provides a predictable positioning accuracy of at least 22 meters (95 percent) horizontally and 27.7 meters vertically and time transfer accuracy to UTC within 200 nanoseconds (95 percent). PPS will be the data transmitted on the GPS L1 and L2 frequencies. PPS was designed primarily for U.S. military use. It will be denied to unauthorized users by the use of cryptography. PPS will be made available to U.S. and military and U.S. Federal Government users. Limited, non-Federal Government, civil use of PPS, both domestic and foreign, will be considered upon request and authorized on a case-by-case basis, provided: < snip > GPS SIGNAL CHARACTERISTICS The satellites transmit on two L-band frequencies: L1 = 1575.42 MHz and L2 = 1227.6 MHz. Three pseudo-random noise (PRN) ranging codes are in use. The coarse/acquisition (C/A) code has a 1.023 MHz chip rate, a period of 1 millisecond (ms) and is used primarily to acquire the P-code. The precision (P) code has a 10.23 MHz rate, a period of 7 days and is the principal navigation ranging code. The Y-code is used in place of the P-code whenever the anti-spoofing (A-S) mode of operation is activated. The C/A code is available on the L1 frequency and the P-code is available on both L1 and L2. The various satellites all transmit on the same frequencies, L1 and L2, but with individual code assignments. Due to the spread spectrum characteristic of the signals, the system provides a large margin of resistance to interference. Each satellite transmits a navigation message containing its orbital elements, clock behavior, system time and status messages. In addition, an almanac is also provided which gives the approximate data for each active satellite. This allows the user set to find all satellites once the first has been acquired. + + + + + + + + + + + + + + + + + + + + + + + + + + + + From: http://tycho.usno.navy.mil/gpsinfo.html RF Jim ----- Original Message ----- From: "Dave Tweed" To: Sent: Saturday, November 23, 2002 9:54 AM Subject: Re: [OT]: (Report of) GPS anomalies > RF Jim wrote: > > 2) the military (and other qualified users) have access to > > a 'chip rate' ten times what civilian users have with approximately > > ten times the accuracy commonly availiable on 'civilian' GPS > > receivers - aren't you? > > This is a common misconception. > > Actually, the chip rate has very little if anything to do with the overall > accuracy; the quality of the correlators and local clock is the real > limitation. The main reason military receivers do better is because they > get access to two different carrier frequencies, which allows them to > measure and compensate for atmospheric refraction in real-time. > > -- Dave Tweed > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads