Patent GB-940292-A (GB)
Title: Improvements in or relating to colision warning apparatus
Inventor: FREEDMAN HAROLD PHILIP
IPC: G01S13/937
Filed: 1958-11-28
Abstract: 940,292. Radio direction-finding and signalling; radar. AVEL CORPORATION GENEVA. Nov. 19, 1959 [Nov. 28, 1958; Dec.11, 1958], Nos. 38513/58 and 40039/58. Headings H4D and H4L. Collision warning apparatus in a first craft comprises means to determine the course and speed of the first craft, means to receive a radio transmission from a second craft giving data regarding the course and speed of the latter, and means to compute the bearing on which the second craft must lie to be on a collision course with the first craft, the computer providing an output signal representing that bearing. The course b and speed V b  data of the second craft are transmitted as pulse pair spacings representing orthogonal components V b  sin b and V b  cos b as described in Specification 897,101, and corresponding voltages are subtracted from the outputs of resolver R1, Fig. 2, representing V a  sin a and V a  cos a where subscript a represents the first craft. Resolver R2 rotor output is amplified and fed to servomotor M which turns that rotor to a null position corresponding to collision bearing x 90 degrees; motor M rotates the null of cardioid-pattern direction-finding aerial DFA in order to ascertain whether a subsequent second craft transmission lies on the collision bearing. The directive device may be the aerial of a rangemeasuring transponder, or a goniometer, or a photo-electric cell movable around the screen of a cathode-ray tube goniometer, or a device responsive to visible or invisible light. In a radio system the second craft pulse train comprises five pulse pairs in seriatim, Fig. 4 (IX), the spacing between second and fifth pulses representing V b  sin b, between fifth and seventh representing V b  cos b, between first and third representing the first digit of a height code and between ninth and tenth representing the second digit of a height code; the pulse train is generated by controlled delay circuits. Fig. 3 (not shown), and the spacing between first and ninth pulses is made long enough to give time for the direction-sensitive device to be trained to the collision bearing. Fig. 5 illustrates the apparatus carried by a craft; receiver Rx1 output passes to coincidence gate 24 which produces a single pulse for each received pulse pair separated from one another by a time corresponding to that of the first height digit of the receiving aircraft, the gate output thus corresponding to the pulse train in Fig. 4 (VI). Decoder 26 separates out the first pulse pair (" origin signal ") of this train and decodes the orthogonal components for computer 27, the output from which causes motor M to position Ae3 null for the collision bearing. The decoder also sends a signal 23 to mute receivers Rx1, Rx2 until the ninth pulse of the train is expected as determined by delayed-pulse generator 28 fed with the first origin pulse from the decoder. If the ninth and tenth pulses originate on the collision bearing the ensuing output of anticoincidence gate 30 passes through gate 29, opened by generator 28, to a coincidence gate 31 directly and via a delay 32 set according to the second digit of the aircraft's own height code so as to actuate warning device 33 only if the other aircraft is on a collision bearing and at about the same height. In an alternative computer the components of velocity Vb are resolved parallel and perpendicular to the course of the first craft. Fig. 6 (not shown); relative closing speed is also indicated. The angular extent over which collision bearing warning is given may be controlled by adjusting the effective diameter of the polar diagram of a fixed rod aerial associated with a rotatable loop aerial to afford a cardioid polar diagram. The aerial for the direction-sensitive device may alternatively be a narrow beam type, anti-coincidence circuit 30, Fig. 5, then being replaced by a coincidence gate. Ranging, Figs. 5 and 7.-The apparatus of Fig. 5 may be modified to allow for range determination as indicated by Fig. 7, in this modification the final two pulses are not transmitted. At the end of the eighth pulse, decoder 26 sends a pulse to a delay circuit 40 long enough to enable aerial Ae3 to be turned into the correct position. At the end of this delay, circuit 40 sends a pulse to a change-over switch 41 to connect aerial Ae3 into circuit; this pulse also passes to an interrogation coder 42 to generate a double pulse (characterizing an interrogation) which is passed to a height coder 43 to generate two pulse pairs at a separation representing the second part of height coding; the two pulse pairs are transmitted. If the second aircraft is on the collision bearing it responds with two pulses which are passed via a height gate 45 from which a single pulse issues to a range gate 47; the latter is opened by the interrogation coder 42 and is closed after a time corresponding to the range of the most distant aircraft that constitutes a collision risk. The gate period may be controlled by the measured closing speed. Switch 41 is arranged to return to its normal condition whereby it connects an omni-directional aerial Ae4 to switch 44. Specification 874,261 also is referred to. Reference has been directed by the Comptroller to Specification 835,185.