Patent GB-1398483-A (GB)
Title: Integrated collision avoidance dme telemetry and synchronization system
IPC: G01S11/08
Filed: 1973-04-12
Abstract: 1398483 Radio navigation J P CHISHOLM 12 April 1973 [26 April 1972] 17667/73 Heading H4D The invention is concerned with an aircraft collision-avoidance or station-keeping, Fig. 4 (not shown), system (C.A.S.) in which participating aircraft time-share a cyclic time-slot cycle providing for absolute clock synchronization to master time, secondary radar distance measuring (D.M.E.) to a transponder at the master time station, and one-way distance measurement between aircraft for collision avoidance. According to the invention each aircraft incorporates occupancy-distinguishing means for distinguishing between portions of the time-slot cycle which must be monitored and utilized for the C.A.S. function and other portions which are available for the D.M.E. function, and means responsive to the occupancy-distinguishing means and operative during the monitored portions to tune the transmitter and receiver to a designated C.A.S. frequency and actuate the C.A.S. means and operative during the available portions to tune the transmitter and receiver to the selected D.M.E. channel. In one embodiment a master clock 12 is provided at a TACAN ground station and in an aircraft the transmitterreceiver tuning is voltage-controlled by a generator 116. The system utilizes a cycle of 2000 time slots each of 1500 microseconds duration, the first time slot of alternate cycles including synchronizing pulses from the ground station which are recognized by a unit 50 in an aircraft for absolutely synchronizing its local clock 42 in association with a D.M.E. measurement utilizing the TACAN ground transponder, see Specifications 1,250,570 and 1,278,636. A one-way ranging unit 60 affords the range of participating aircraft from "own" aircraft. Data including range and altitude is digitally telemetered to the ground station such that a computer 16 can provide a location display 18 of all participating aircraft, and the ground station telemeters instructions to specifically addressed aircraft. Occupancy-distinguishing.-In the embodiment it is arranged that during some time-slot cycles no D.M.E. function is carried out but "listens" and performs the C.A.S. function and in the remaining time-slot cycles the C.A.S. function is performed in those time-slots found to be occupied and permits the D.M.E. function in the other, unoccupied, time-slots; the two types of cycle are generated by a bistable 102. Logic means includes a circuit 90 counting out 2000 slots but two slots earlier than circuit 46 is provided for distinguishing occupancy; a "threat evaluation" circuit 63 may be added to inhibit the D.M.E. function only if there is a substantial danger of collision. Transmitter-receiver tuning.-After manual selection of the desired D.M.E. and C.A.S. channels, transmitter-receiver tuning switching between the two functions is accomplished by a bi-stable 112. A re-tuning time of 20 microseconds may be used and if a maximum range of 100 miles is needed for C.A.S. purposes the early part of a time-slot may be utilized for C.A.S. threat evaluation and the remainder of the slot for the D.M.E. function after a collision threat has been determined not to exist. Random operation.-A noise generator enabling or blocking an AND gate at random comprises a circuit 101 may be incorporated, to ensure that aircraft do not perform D.M.E. functions simultaneously.