Patent GB-912501-A (GB)
Title: Transponder ranging apparatus
Inventor: VIELLE EUGENE EMILE
IPC: G01S13/933
Filed: 1958-05-12
Abstract: 912,501. Transponder apparatus; radio navigation. AVEL CORPORATION GENEVA. April 30, 1959 [May 12, 1958], No. 15189/58. Classes 40 (5) and 40 (7). Relates to transponder ranging and warning apparatus for use in the avoidance of collisions between ships or aircraft and provides a different warning time in accordance with whether the interrogations and responses are accepted from the front or the rear of the co-operating vessels. As shown in Fig. 1 the interrogator in an aircraft comprises a transmitter TX1 to which pulses are applied from a generator PG1 via a height coder HC1 controlled by a height-sensitive device H1, the pulses being radiated as pairs of pulses separated by a time interval t h  characteristic of height on a frequency f1 from an omnidirectional antenna A5. The responder in an aircraft, Fig. 2, comprises directional antennae A3, covering the forward sector and A4 covering the rearward sector, the two sectors overlapping, and each antenna being connected through its own buffer amplifier BA3, BA4, to a receiver RX6 providing A.G.C. for receivers RX3, RX4. The antennµ A3, A4, are also connected via fixed delay circuits D8, D9, to the respective receivers RX3, RX4, the arrangement being such that when an interrogation signal arrives after a delay t 0  due to the distance between the two aircraft only the receiver RX3 or RX4 receiving the stronger signal is effective. The outputs of the receivers RX3, RX4, are respectively connected to variable delay devices D3, D4, controlled by an air speed servo AS2 so that the delay device D3 produces a delay t 3  decreasing as the aircraft speed increases, and the device D4 produces a delay t 4  increasing as the speed increases. The delay t 4  is greater than the delay t 3  for equal speeds. Each delay device D3, D4, is connected to its respective height gate HG3, HG4, which are set by a height-sensitive device H2, the arrangement being such that a pair of pulses arriving at the input of the height gate produce a single output pulse, if the two aircraft are within the same height range. Assuming that A3 receives the stronger signal the input to HG3 will be a pair of pulses spaced by an amount representative of height, the first pulse arriving at a time t 0 +d+t 3  after transmission, where d is the delay introduced by D8 or D9. The output will be a single pulse occurring at a time t 0 +d+t 3 +th after transmission. The outputs from the height gates HG3, HG4, are connected to a height coder HC2, similar to HC1, to generate a pair of pulses representing height which are transmitted on a frequency f 2  from the antenna A6. The interrogator aircraft is provided with similar equipment to that shown in Fig. 2 including antennµ A 1  receiving from the forward sector, and A 2  receiving from the rearward sector, receiver RX5 providing A.G.C., buffer amplifiers BA1, BA2, receivers RX1, RX2, fixed delays D6, D7, and variable delays D1, D2, producing delays t1, t 2 , respectively controlled by an air speed servo AS 1. The delay t 2  is greater than the delay t 1  for equal speeds. If A1 receives the stronger signal the first pulse of the pulse pair at the output of the delay device D1 will appear at a time 2t 0 +2d+t h +t 1 +t 3  after transmission and the pulse pair will produce a single pulse in the height gate HG1, which is further delayed by a time t h . Two height gates may be provided as in Fig. 2. The output of the height gate HG1 is supplied to a range gate RG whitch is opened by a pulse from the generator PG1 for a time representing the maximum delay requiring consideration, the pulses from PG1 being passed via a delay device HD controlled by the height-sensitive device H1 so as to introduce a delay of 2t h  and via a fixed delay D5 introducing a delay of 2d. The delay device D5 controls a flip-flop FF1 to produce a long pulse for the total reception time which is of interest. The flip-flop may be height-controlled to provide increased manoeuvre time at high altitudes. The range gate RG actuates a warning device W which may switch on more accurate direction finding and data exchange apparatus. In a modification, Figs. 4 and 5 (not shown), a single rotating antenna co-operates with a single receiver and a delay device in which the amount of delay is varied cyclically in accordance with the position of the antenna and also is varied according to the speed. The delay devices may consist of a magrietic drum in which either the record of playback head is movable. If the pilot requires to climb or dive the height gates and coders may be offset so as to search at a height other than that at which the aircraft is flying, Fig. 9 (not shown), the arrangement being such that the range of height codings accepted increases with the distance between the two aircraft. Provision may be made for switching out the various delay circuits so that the true range may be determined or additional circuits may be provided giving the true range. In the case of ships the height coding facility is omitted. Specifications 659,007, 874,261, 887,861, 887,864 and 897,100 are referred to.