Patent GB-1071171-A (GB)
Title: Radio communication system
Inventor: EARP CHARLES WILLIAM
IPC: G01S1/40
Filed: 1963-03-01
Abstract: 1,071,171. Radio position ending; radio signalling. STANDARD TELEPHONES & CABLES Ltd. Feb. 28, 1964 [March 1, 1963], No. 8314/63. Headings H4D and H4L. In a radio communication system wherein exclusive communication can be obtained between a ground station and a selected craft or vehicle, the ground station comprises means to determine a co-ordinate of the position of the craft or vehicle and means to control the position of a singularity in an electromagnetic radiation field in dependence upon the determined co-ordinate, such that it includes the craft or vehicle within its area. The detection at the craft or vehicle of the singularity causes the opening of a channel to communication signals from the ground station. In a first embodiment the ground station, Fig. 1, comprises a control centre (1) for determining the co-ordinate, and spaced master and slave transmitting stations (2) and (3) respectively for setting up said singularity. The control centre (1) comprises a P.P.I. radar display (4) showing the response of the craft to be communicated. Two cursor lines (5) and (6) are marked on transparent overlays pivoted about points (7) and (8) respectively corresponding on the sale of the display, to the positions of the two transmitting stations (3) and (2). Each overlay is connected to a servo transmitter (11) and (12) which feed signals to servo receivers (14) and (16) at the transmitting stations (3) and (2), which control in turn the radiating directions of highly directive antennµ (26) and (19), via motors (23) and (17). The overlays are manually adjusted so that the cursors intersect over the response of the aircraft. This causes the beams produced by the antennµ (26) and (19) to be positioned such that they cross at the craft. The master station (2) includes a generator (21) producing a signal F at frequency -. This signal is frequency 2 doubled and amplitude modulated with speech fed from the control centre by land line (33) in means (22), and the resulting amplitude modulated signal at frequency F is radiated by antenna (19). The slave station (3) comprises an audio frequency generator (27) producing sig- #F nals at frequency -- which are fed to one in- 2 put of a frequency changer (28). The output of generator (21) is also radiated from antenna (31) and is received at the slave station and fed to the second input of the frequency changer (28). A signal at a frequency of F + #F is taken from the output of the frequency changer and fed, via amplifier (29), to antenna (26). A band stop filter (34) cuts out any speech component at frequency #F. At an aircraft positioned at the inter-section of the two radiated beams, receiving means, Fig. 2, are provided, wherein the amplitude modulated signal at frequency F, and the signal at frequency F + #F are received in an amplitude modulation radio-receiver (40) to produce the speech modulation and a signal at frequency F. The latter signal passes, via audio band-pass filter (44) and tone rectifier (52) to energize relay coil (42). Energizing the coil closes contact (46), energizing a warning light (47), and closes contact (51) so that the speech signal can pass, via bandstop filter (50), rejecting signals at frequency F, to earphones (49). A general broadcast to all the aircraft in a given area can be made by unidirectional radiation of speech signals for which a tone of frequency F is superimposed. In a second embodiment, the ground station, Fig. 3, comprises a control centre (101) and three spaced transmitting stations (102), (103) and (104). A P.P.I. display (105) is provided with mechanical indexes comprising marker means slidable along radial carriers pivoted at points (106), (107) and (108) representing the three spaced transmitting stations. The indexes are connected to delays (114), (115) and (116) such that the time delay introduced by any one delay associated with a particular transmitting station is proportional to the sum of the displacements of the indexes marker means associated with the other two transmitting stations along their respective radial carriers. The delays are introduced in the circuit between a pulse generator (117) and the three transmitting stations. The delayed pulses are radiated with carrier frequencies #1, #2, and #3 from the three transmitting stations (102), (103), and (104) respectively. The speech signal is radiated from the control centre by a transmitter (122). The pulses from the three transmitting stations are only received simultaneously at the point corresponding to intersection (109) of the marker means of the three indexes. One index only may be used and its displacement from the three points (106), (107) and (108) computed. At an aircraft positioned at the said point of simultaneous reception, the three pulse signals and the speech signal are received and converted to IF signals in amplifier/ converter (131), Fig. 4. The three pulse signals are then fed, via detectors (132B), (132C) and (132D) to a coincidence gate (133). Simultaneous reception of the three pulse signals causes the coincidence gate to energize a relay coil (134), causing the energizing of light (137) and the closing of the speech channel, comprising detector (132A), audio amplifier (139), switch (142), and earphones (143). In a modification of the second embodiment, Figs. 5 and 6 (not shown), the pulse signals may be transmitted with the same carrier frequency, but the pulse signal fed to delay (115), Fig. 3, is delayed by a period T from that fed to delay (114), and the pulse signal fed to delay (116) is delayed by 2T from that fed to delay (114). In the aircraft a single IF detector is used for all three pulse signals and delays of 2T and T are inserted in two of the inputs to the coincidence gate (133) to neutralize the T and 2T delays inserted at the ground station. A general broadcast to a number of aircraft can be made by transmitting three trains of pulses from the control centre, spaced by the delays of T and 2T. The pulses arrive at the aircraft to open the speech path. In a third embodiment, Fig. 7, use is made of the fact that when an antenna, radiating a constant frequency signal, is oscillated along a line with simple harmonic motion, phase modulation is produced in the radiated field at all points except those along the perpendicular bisector of the antenna's path. The master station (301) comprises a linear array of antennµ (303) fed by capacitive commutator means (304) so that, by oscillating the movable plate (306) along the fixed plates (305) the linear antenna oscillation is simulated. The slave station (302) comprises a similar linear antenna array and commutating means whereby a second linear antenna oscillation can be simulated. The two antenna arrays are orientated such that their perpendicular bisectors intersect at the aircraft to be communicated. The master antenna array is energized by a signal at a frequency F amplitude modulated by the speech signal and the slave antenna array is energized by a signal at a frequency F + #F, produced in the same manner as in the embodiment of Fig. 1. The commutation of the two moving plates (306) is controlled by audio generators (307) and (308) such as to be in quadrature. In the aircraft to be communicated with Fig. 8 (not shown) the two received signals beat together to produce the speech signal and the signal at frequency #F. Lack of phase modulation of the latter signal is detected by a phase modulation detector and #F signal detector. No output from the phase modulation detector together with some output from the #F signal detector causes a gate to energize the speech passing relay. In a fourth embodiment, Fig. 9 (not shown), the antenna arrays are each replaced by a single antenna rotating in a circle, fed with a signal whose phase is varied in such a manner that the produced radiation field corresponds to an antenna oscillating in a straight line. Alternatively the rotating antennµ may be replaced by two circular antenna arrays with commutating feeding means. In an unillustrated embodiment the ground station and aircraft carry highly stable signal sources which are initially phase synchronized. The highly stable signal source at the ground station is used to amplitude modulate a highly directional beam after having been phase shifted by an amount representing the distance of the desired aircraft, the beam being directed with the determined bearing of the aircraft. The phase of the amplitude modulation of the beam when received by the aircraft is thus equal to the phase of the output of the aircraft's highly stable signal source.