Patent GB-897101-A (GB)
Title: Improvements in collision warning apparatus
Inventor: FREEDMAN HAROLD PHILIP
IPC: G01S13/933
Filed: 1958-04-11
Abstract: 897,101. Anti-collision radio systems. AVEL CORPORATION GENEVA. April 3, 1959 [April 11, 1958], No. 11603/58. Classes 40(5) and 40(7). [Also in Group XXXVI] In a system for giving a warning on a Master craft B, Fig. 1, if it is on a collision course with reference to an Intruder craft A, the Intruder craft A transmits by radio to the Master craft B data indicating its speed VA and heading a and the Master craft B determines (1) its own speed VB and heading b and (2) the relative and true bearings d and (b+d) of the Intruder craft A and computes the components C and D of the relative velocity of the two craft resolved respectively perpendicular and parallel to the line of sight BA according to the equations a warning indicating the danger of collision being produced if C = O and D # O. The velocity data of the Intruder craft A is transmitted in the form of orthogonally resolved components V A  sin a, V A  cos a by pulse space modulation; alternatively pulse-duration, pulsecode or frequency modulation may be employed. In the aircraft system described the Master craft B carries a scanning pulse radar CCW, Fig. 2, with a P.P.I. display operating at a radio frequency f1 and the intruder craft A carries a transponder, Fig. 3 (not shown), which, in response to each interrogating pulse, transmits at a radio frequency f2 a reply signal comprising two identical groups of four pulses, Fig. 5 (not shown), spaced apart by an interval proportional to the height of the craft A, the spacing between the first and second pulses of each group being fixed and the spacing between the second and third and between the third and fourth being proportional to VA sin a and VA cos a respectively. Reply signals having a coding corresponding to the height of the Master craft B are received at the craft B by an aerial A4 and receiver Rx3 and are selected by a height gate HG controlled by an altimeter H and voltages VA sin a and V A  cos a produced by decoders Dl and D2 are applied to an electronic computer EC, Fig. 4 (not shown) (see Group XXXVI), together with voltages sin (b+d), cos (b+d), V B  sin d, V B  cos d produced by resolvers R1-R4 having inputs VB, b and d from the airspeed meter AS, compass CR and radar aerial Al, the output from the computer EC being applied to a warning indicator W. As shown in Fig. 2 the angle d is the instantaneous position of the radar aerial A1; alternatively if the responsor Rx3 is provided with a rotating directional aerial A4 then the angle d may be the instantaneous position of the aerial A4. The Master craft B also carries a transponder Rx2, Tx2 similar to that carried by the Intruder craft A so that the craft B can co-operate with other interrogationequipped Master craft, the reply signal transmitted by Tx2 being coded in accordance with V B  sin b, V B  cos b and the height of the Master craft B; a muting signal from the pulse generator P9 of the radar CCW is applied to the transponder receiver Rx2 to prevent triggering by the transmitted radar pulses and a fourth muting signal (not shown) may be applied to the receiver Rx3 to include reply signals from craft beyond a safe distance. The pulse spacing coders and decoders comprise conventional arrangements of adjustable delay lines (e.g. as in Specification 659,007) and coincidence circuits illustrated in Figs. 5 and 6 (not shown). If required the interrogating pulses from the radar CCW may be coded in frequency, pulse duration or pulse spacing as in Specification 897,100 the transponder being arranged to reply only to signals with a height code corresponding to the height of the transponder. Specifications 838,034, 874,261 and 874,263 also are referred to.