Patent GB-874268-A (GB)
Title: Improvements in proximity warning devices
Inventor: VIELLE JOHN
IPC: G01S13/933
Filed: 1958-02-12
Abstract: 874,268. Combined radio receiving and transmitting systems; radio direction-finding. AVEL CORPORATION GENEVA. Feb. 2, 1959 [Feb. 12, 1958], No. 4616/58. Classes 40(5) and 40(7) Relates to a proximity warning device for aircraft which includes a transmitter receiver combination, the receiver and transmitter being switched alternately, wherein a height-sensitive device controls the frequency of an oscillator which drives the transmitter and also controls the tuning of the receiver. Fig. 2 shows the control circuit arrangement carried in an aircraft, in which a low frequency random frequency source I controls the switching of a multivibrator 4 via a normally open gate circuit 3 and amplifier 2 whereby a switch 5 is put alternately to the transmit or receive position. With the switch 5 in the transmit position a signal is sent to a coder 6 controlled by a compass repeater 7 whereby a pulse of length characteristic of the course is caused to energize a relay RL2 for the duration of the pulse and switch on the transmitter for that period. The pulse from the coder 6 is differentiated and clipped at 8 so that at the end of the pulse, after the relay RL2 has released momentarily, a coder 9 driven by an air speed repeater 10 operates the relay RL2 as before. At the end of the second pulse RL2 releases and a pulse from the coder 9 resets the switch 5 to the receive position. The receiver output is supplied via a point 0 to a pair of decoders 11, 12, for course and speed, and to a differentiator and clipper 13 which controls the multivibrator 4. When a sufficiently strong signal is received a negative voltage appears at the point 00 and blocks the gate 3 to prevent the source 1 from controlling the multivibrator 4. At the end of the received pulse the differentiator 13 causes the multivibrator 4 to operate the switch 5 to the transmit position. The voltage at the point 00, which has a long decay time holds the gate 3 closed during the subsequent transmitting period. In the transmitter-receiver, Figs. 1A, 1B, 1C, a height sensitive unit H operates a variable capacitor VC1 controlling the frequency of an oscillator V21, which varies from 170 kc./s. to 200 kc./s. according to the altitude, a diode V22 acting as an amplitude limiter. The output of the oscillator V21 is supplied via a line L to a mixer V19 which also receives a 2À8 mc./s. input from a crystalcontrolled oscillator V20. The output of the mixer V19 (2À97 to 3À0 mc./s. according to height) is supplied to a transmitter Tx via a relay contact RL2c of the relay RL2 (Fig. 2), contacts RL2a and RL2b also being closed during transmission. The receiving portion includes a rotatable loop antenna Al driven by a motor M1, and a fixed sensing antenna A2. The signal supplied from the antenna Al is given a 90 degrees phase shift via V1 and the valves V3, V4, which are also supplied with the output at 100 c/s. from a square wave generator V11, V12, cause the signal appearing on the line A to be phase inverted every five milliseconds. The signal on line A is supplied to one primary winding of a transformer T1, the signal supplied by the fixed antenna A2 being amplified at V10 and supplied via line D to the other primary winding. An intermediate frequency of 470 kc./s. is supplied by an oscillator V14 to a mixer V13 and an output from the mixer V19 is supplied via line J to the mixer V13. Frequencies in the range 3À44 to 3À47 mc./s. are selected by a band pass filter T2 and supplied to the mixer V5 which is also supplied by the transformer Tl. Since the received frequency is in the range 2À97 to 3À0 mc./s. the output of the mixer V5 will be 470 kc./s. plus or minus a frequency which depends upon the difference in height between the two aircraft. It is assumed that if the difference between the transmitted and received frequencies is less than 250 cycles per second the aircraft are dangerously close in height, and the output of the mixer V5 is passed via. a filter selecting frequencies of 470 kc./s. plus or minus 250 c/s. and an I.F. amplifier V6, to the lines M and N. The signal on line N is supplied to a detector V7a and the 100 c/s. component from the detector is fed via an amplifier V25 to a control winding of the motor M1 A further winding of the motor receives a 100 c/s. reference frequency from the valve V12 via line K and valve V24, whereby the motor operates to bring the antenna A1 to a null position. The negative component at the anode of V7a is applied via a valve V9a and filter L2, C3, C4, C5, rejecting the 100 c/s. signal, to drive the output 0 negative with respect to earth, the output 0 being connected to the decoders 11, 12, Fig. 2, and to the differentiator 13. The output 0 is also applied via a diode V7b to provide A.G.C., and via a valve V 9b which normally holds a relay RL1  energized, causes relay RL1 to release. Contact RL1a holds a mixer valve V17 cut off under no-signal conditions. When a signal is received a negative control voltage from a diode V8b is fed via contact RL1c to point 00 to control the gate 3, Fig. 2. An oscillator V16 provides an output at 469À5 kc./s. which, when the relay RL1 releases, is fed via contacts RL1a to the mixer V17, which also receives a signal on line N from T4, and the output from V17 (500250 c/s.) is fed via a thermistor Th1 to a valve V18 whereby a reading is produced on an indicator 1 showing the relative height separation of the two aircraft. A light LP1 is energized through contact RL1b only when signals are being received. A relay RL3 is energized by the valve V25 and through contacts RL3a prevents operation of the collision warning circuit until the antenna A1 has homed.