Abstract: An accurate location system 10 for use in locating the position of a tracked unit 16 having at least a first and a second transmitter 14, 22 for propagating at least first and second signals and a master station 12 for receiving and storing the first and second signals, respectively. The tracked unit 16 receives and operates on the first and second signals from the first and second transmitters 14, 22, respectively, for providing third and fourth signals which are transponded to the master station 12. A correlation detector 40 located within the master station 12 receives and cross-correlates the transponded third and fourth signals with the stored first and second signals within the master station for determining the additional times of flight (.tau.) of the third and fourth signals transponded to the master station. The locus of points of constant (.tau.

Abstract: A vehicle locating system (VLS) comprises a large number, for example, several million, vehicle-mounted transmitters and several benchmark transmitters; first, second and third signal relay stations and a central processing station at which the transmitter locations are determined, the central station being connected by conventional links to subscriber stations. One hundred microsecond-long RF signals are transmitted by each transmitter in a non-synchronized, mutually random manner. Each signal comprises a 20 microsecond synchronization symbol followed by six, four bit transmitter indentification symbols, each of ten microseconds length. Following the indentification symbols are 10 microsecond message and processing symbols. The control station includes correlation means for correlating the synchronization symbols on each relayed signal against stored data to identify the beginnings of the signals.

Abstract: Rapid frequency synthesizer apparatus, particularly for use in high speed frequency hooping systems, includes a voltage controlled oscillator (VCO) and a memory in which are stored digital control voltage commands corresponding to the various frequencies to be synthesized by the VCO. A controller, responsive to channel selection commands, addresses the memory and causes the corresponding digital control voltage command to be generated. A digital-to-analog converter receives the digital control voltage command and converts it to an analog control voltage signal which is fed to the VCO. The resulting VCO output signal, at frequency, f.sub.out, is compared in a frequency counter with a reference frequency f.sub.R. The controller controls operation of the frequency counter so that a difference between the actual synthesized frequency and the programmed frequency is determined.