Patent GB-912502-A (GB)
Title: Improvements in proximity warning devices
Inventor: VIELLE EUGENE EMILE
IPC: G01S13/935
Filed: 1959-07-03
Abstract: 912,502. Transponder apparatus; radio navigation. AVEL CORPORATION GENEVA. June 30, 1960 [July 3, 1959], No. 23006/59. Addition to 912,501. Classes 40 (5) and 40 (7). The apparatus of the parent Specification for use in the avoidance of collisions between ships or aircraft is modified to give a warning signal when an aircraft is in dangerous proximity to a ground obstacle. In the aircraft, Fig. 1, a pulse generator PG1 feeds pulses to a height coder HC1 controlled by a height-sensitive device H1, and the output from the coder, a pair of pulses separated by an interval characteristic of height, modulates a transmitter TX1 radiating the interrogating signal at a frequency #1 from an omni-directional antenna A3. At the beacon, Fig. 2, the signals are supplied via an omni-directional antenna to a receiver RX3 and the output of the receiver is fed through a delay device D6, giving a delay D, to a height gate HG2 which is controlled by a height-sensitive device H 2  as in the parent Specification so that a predetermined range of height codings is accepted. The output of the height gate HG2, consisting of full line pulses aa, Fig. 4, are passed through a diode X1 and also through a fixed delay D7 and diode X2 to the transmitter TX2, the dotted line pulse aa delayed by an amount t c  showing the pulse at the output of the delay line D7. The signals from the height gate also pass through a height delay HD2 set by the height-sensitive device H2 to produce pulses bb delayed by an amount t h  characteristic of the beacon height and via a diode X3 to a pulse widener PW2 and via a fixed delay D8, producing dotted line pulses bb delayed by an amount t c , and diode X4 to the pulse widener. The delay t c  is characteristic of all beacons using the system. - The pulses cc are radiated by the transmitter TX2 on a carrier frequency # 2  and received by directional antennµ A1, A2, in the aircraft. Buffer amplifiers BA1, BA2, and receiver RX4 control the gain of receivers RX1, RX2, as in the parent Specification, so that only the receiver receiving the stronger signal will be operative. The signals from receivers RX1, RX2 are fed to respective delay devices D1, D2, controlled by an airspeed sensitive device AS1, the signals also being given a delay in accordance with the direction of reception. A height gate HG1, similar to height gate HG2 is controlled by the device H1 to give a delay t hh  to the signals from D1 or D2 which is characteristic of the aircraft height, and includes a coincidence gate so that if the delay thh is approximately equal to the delay t h  the first and second delayed pulses dd and the third and fourth undelayed pulses cc will produce output pulses ee separated by a time t @c  characteristic of the beacon. The pulse widening at the beacon enables coincidence to occur at a range of values of t hh . The output of the height gate HG1 is passed to a range gate RG operated by pulses from PG1 delayed by a height delay giving a delay of 2t hh  and a delay device D5 giving a delay 2D, which control a flip-flop FF1 as in the parent Specification. The signals from the range gate are supplied to a decoder DC incorporating a fixed delay t c  producing pulses ff and a coincidence circuit, so that if coincidence occurs between delayed and undelayed signals a signal gg is produced and operates a warning device BW. A device WM connected to the input of the height gate measures the width of the received pulses so that if the device BW is operated and the device WM shows that the minimum safe height is given by the width of the received pulses is above that set by the pilot as his maximum height a " turn " warning device TW is actuated. In an alternative arrangement, Figs. 5 to 9 (not shown), pulse widening is dispensed with and a sequence of three pulses is transmitted instead of four. The warning time is made proportional to the component of velocity of the aircraft towards the beacon, or another aircraft. The pulses from the beacon are given a spacing which is characteristic of the beacon. Additional facilities include means for determining the relative bearing of the beacon, for indicating how far it is necessary to climb in order to clear the obstruction, and for indicating how far the aircraft is inside the danger zone.