Kenwood TH-D72A/E User Manual

Also see for TH-D72A: Instruction manual Instruction manual Instruction manual Instruction manual Service manual

Contents

24 CONTENTS TH-D72A/E4 GPSGPS, standing for Global Positioning System, is becoming common nowadays and following is a briefintroduction.The American Defense Department developed GPS originally for military operations. The system isavailable for use by the general public. For example, anybody can use GPS in association withmodern vehicle navigation systems. Position precision for public use is 15 m or 50 feet. Moreover,precision can be improved when used for vehicle navigation and aboard ships through use of mapmatching technology and differential GPS techniques.A total of 24 or more GPS satellites are at a high-level altitude of approximately 20,000 km or 12,500miles on six circular tracks with orbital radii of approximately 26,000 km or 16,200 miles. Therefore,there are four or more satellites located in each orbital track. GPS typically operates at the frequencyof 1575.42 MHz with the bandwidth of 2.046 MHz. Because multiple GPS satellites transmit signalsat the same frequency, spread-spectrum (SS) modulation is used. Due care must be taken wheninstalling amateur radio equipment and antennas for use on the 430 MHz or 1200 MHz bands toprevent from interfering with GPS signals.Figure 4-1 GPS IIR Satellite in OrbitThe GPS receiver receives the radio signals transmitted from the GPS satellites and measures thetime duration between when the signal leaves the satellite and when the signal arrives at the GPSreceiver. The receiver measures the time duration between when the signal leaves the satellite andwhen the signal arrives at the GPS receiver. Knowing this time allows calculation of the distance thatthe signal traveled from that particular satellite. By receiving multiple signals from different satellitesand doing this distance calculation multiple times, the intersection of the spherical surfaces thatrepresent the respective radius distances to the various satellites will determine a single point. Theprecision of the determination of the intersecting point relies on the satellites and the data collected.4.1 What is GPS?4.1.1 Position Determination Principle