An apparatus for locating a large number of cooperative targets consisting of a ground-based master station, three airborne repeaters and as many transponder units as there are cooperative targets. The master station transmits pulses, which are received by the repeaters. The repeaters in turn transmit the pulses at a second frequency. The transponders and the repeaters transmit back to the master station. By accurately measuring the time required for the pulses from the transponders and repeaters to return, the location of each cooperative target can be determined.
An aircraft identification (IFF) system involving ground interrogating stations and multiple airborne transponders. At least one interrogating digital code preceded by a synchronizing pulse sets up a sequence whereby replies are transmitted in the order of their reception at each airborne transmitter. Thus, multiple interrogation can be handled with higher response probability than heretofore. Digital logic is provided for selection of predetermined reply codes and their order and time of transmission from each airborne transponder.
A dual frequency ranging and communication system for communicating with and locating mobile vehicles in a multipath environment such as an urban center. This system functions in urban areas for both communication and ranging where line of sight radiation techniques may not properly function. A plurality of remote relay stations are located at points throughout the urban area, each station receiving and transmitting coded digital data and tone signals, the tone signals being used for phase ranging. Each of the vehicles is equipped with a transponder responsive only to the radio signal having a formatted message including the vehicle identification code with a ranging tone suitably impressed thereon. The formatted signal is transmitted from one of the relay stations at a first frequency and picked up by a preselected number of other relay stations as well as by the vehicle transponder. The vehicle transponder in turn generates a reply signal at a second frequency containing message data and a tone signal modulated on the second frequency for use in ranging, all of which signals are processed at a central location.
In an interrogator-transponder collision avoidance system a probe selector etects the presence of two distinct signals, P or Q. Detection of a P signal at the input dictates a Q output and vice versa. Additional circuitry resolves ambiguity when P and Q appear concomitantly. In the absence of either P or Q at the input, the output is randomly chosen to be either P or Q.
In an interrogator-transponder collision avoidance system a probe selector etects the presence of two distinct signals, P or Q. Detection of a P signal at the input dictates a Q output and vice versa. Additional circuitry resolves ambiguity when P and Q appear concomitantly. In the absence of either P or Q at the input, the output is randomly chosen to be either P or Q.
The position of a ship or other object being located is determined at an earth station using an active ranging satellite and a satellite which transmits time signals. One line of position is determined by two-way active ranging through the first satellite. The other line of position is determined by one-way ranging from the second satellite. The time interval between the time of arrival of the timing signal at the ship and reception of the active ranging signal at the ship is measured and sent back to the earth station with the ship's active ranging response. The position fix is then computed at the earth station.
