Patent GB-774472-A (GB)
Title: Systems for establishing and maintaining communication between beam-emitting stations
IPC: H04B10/11
Filed: 1951-01-12
Abstract: 774,472. Photo-electric communication detection systems. TOUVET, G. Jan. 12, 1951, No. 884/51. Class 40 (3). In a system for automatically establishing and maintaining communication between two stations, each of which embodies a receiver together with a transmitter emitting a beam of radiation divided into solid-angle zones distinguished by characteristic frequencies, each station is provided with a control device for automatically controlling azimuth and/or elevation the direction of the beam emitted by it, each control device being governed by the frequency characterizing that zone of an incident beam which impinges on the associated receiver and being arranged so that the beams emitted from the two stations are automatically brought into substantial alignment with one another by a process of mutual correction applied to the angular deviations of the beams. Fig. 1 shows an optical transmission assembly for communicating intelligence over an infra-red or ultra-violet radiation beam wherein sectorshaped gas discharge tubes 1, 2, 3, 4 of the kind described in Specifications 774,471 and 774,475, [both in Group XXXV], energized at radio frequencies F 1 , F 2 , F 3 , F 4'  from control transmitters T 1 , T 2 , T 3'  T 4  are circularly disposed, while a tube 5 is arranged at the centre of the circle and also as an outer circumferential ring, and energized at frequency F 5  from a transmitter 5 which is modulated to communicate intelligence. The assembly is placed at the focus of a reflector to transmit a composite beam of radiation elements modulated at F 5  at the centre and periphery of its cross-section and at control frequencies F 1  to F 4  in the intermediate sectors disposed about its centre (Fig. 2). The remote receiver responsive to the beam of radiation may be directional or non-directional and comprises an array of photo-cells aligned similarly to the transmitting tubes, or a single photo-cell connected to multi-channel frequency selective output circuits. At each of two co-operating stations the transmitters and receivers are rotatably mounted on platforms 6, 7 (Fig. 3, 11) by a continuously-running motor 8 and a reversible motor 9 operating at, e.g., 10 times the speed so that when out of contact with a remote station the horizon is continuously traversed through 360 degrees during which motor 9 is energized from power lines 17, 18 through contacts 20 of relay 22 and motor 8 is energized through mechanically-operated contacts 13. When the local receiver is traversed through the searching beam of a distant transmitter, photocell 21 picks up the outer ring of the radiation beam modulated at F5 and energizes receiver R5 tuned thereto to operate relay 22 which holds over normally closed switch 25 and contacts 23. Contacts 20a open and 20b close to stop the continuous rotation of motor 9 and transfer its control to relays 27, 28. Contacts 29 close to energize electromagnets 11, 16 which respectively de-energize motor 8 at contacts 13, disconnect it mechanically from platform 6 at clutch 12, interlock platforms 6, 7 for unitary rotation by pin 14, and also engage a movable brush 15 with a segmented contact disc 15a carried by platform 7. Reception of a radiation element modulated at F 2  by photo-cell 36 energizes receiver R 2  tuned thereto to operate relay 37, which holds over normally closed changeover switch 40, and contact 38, and normally closed contacts 41 of relay 42. Normally closed contacts 43 in the holding circuit of relay 42 open, and contacts 44 close to energize relay 27 through the normally closed changeover switch 32 and normally closed contacts 45 of relay 28. Relay 27 operates, holds over contacts 46, opens contacts 47 to disable relay 28, and closes contacts 49 to energize motor 9 for anticlockwise rotation through contacts 20b operated by relay 22. Reception of a radiation element modulated at F 4  by photo-cell 50 energizes receiver R 4  tuned thereto to operate relay 42, which holds over normally closed changeover switch 53, contacts 51 and normally closed contacts 43 of relay 37. Normally closed contacts 41 in the holding circuit of relay 37 then open, and contacts 48 close to energize relay 28 through the normally closed changeover switch 33 and normally closed contacts 47 of relay 27. Relay 28 operates, holds over contacts 54, opens contacts 45 to disable relay 27, and closes contacts 55 to energize motor 9 for clockwise rotation through contacts 20b as before. Thus the motor rotates in either direction in accordance with the sense of the misalignment of the receiver photo-cell array with the incident beam from the remote transmitter and rotates the interlocked local receiver and transmitter in such a direction as to restore coincidence of orientation with the beam. Motion continues until the brush 15 contacts a segment of disc 15a to energize coil 30 which changes over switches 32, 33, to instantaneously break the holding circuits of relays 27, 28, which are then selectively reenergized according to the instantaneously prevailing misalignment to drive the motor clockwise or anticlockwise another step according to the reception of radiation by photo-cells 36 or 50, in dependence on the deviation of the incident beam. Thus the local receiver and transmitter are together orientated step-by-step towards the centre of the incident beam from the remote station and the remote receiver and transmitter are similarly orientated on to the incident beam from the local station. Changeover contacts 40, 53 are operated at timed intervals greater than twice the period of operation of changeover switches 32, 33 by, e.g., a bimetallic thermal element or a second ring of segments rotated by platform 7, to release relays 37, 42 and thus sequentially test the system for coincidence with the incident beam. at which coincidence only the element of radiation modulated at F 5  is received and relays 42, 37 are accordingly inoperative. At coincidence the operation of switches 40, 53 breaks the relay holding circuits so that relays 42, 37 and relays 28, 27 are de-energized, and the motor is stopped at the next periodic opening of switches 32, 33 so that the local receiver and transmitter are held in alignment with the incident beam. If misalignment exists it is corrected by further sequential operation of the traversing motor in alternate directions as described, and the remote receiver and transmitter are similarly maintained in alignment with their incident beam. A further relay 80 in the energizing circuit return of relays 42, 37 may be energized by an additional photo-cell and receiver responsive to an additional radiation element of frequency F 5  in the centre of the beam, to de-energize both relays and stop the motor on coincidence being attained. Vertical alignment may be attained by a similar arrangement of receiving photocells and control circuits responsive to radiation elements of frequencies F 1 , F 3  and aligning the transmitters and receivers with the incident beam in elevation. After correct alignment, information or control signals may be transmitted utilizing the modulation F 5  of the radiation element of the centre of the beam. On completion of a transmission, switch 25 is opened to release relay 22, unlock platforms 6 and 7, and return the system to continuous search operation. The switch may be automatically actuated after a predetermined delay time, to prevent the loss of potential contacts with other stations by operation of the switch before complete alignment has been achieved. The transmitters and receivers may be fixed and the emitted and incident beams rotated by optical director members such as mirrors in the radiation paths. The transmitter and receiver rotational interlock may be electrical instead of mechanical, e.g. by means of a selsyn system maintaining their axes parallel during rotation. In a modification of the motor control circuit (Fig. 8 not shown) the orientation movement of the transmitter and receiver at each station is carried out continuously (instead of in a step-bystep motion) until alignment is obtained. More accurate alignment may be obtained by the use of composite beams comprising more complex patterns of modulated radiation elements (Figs. 7a, 7b, 9a, not shown) and for horizontal alignment only, the modulated radiation elements may be distributed along a rectangular band (Fig. 9b, not shown), appropriately modified motor control circuits being employed (Figs. 6, 10, not shown). The relays are replaceable by thyratrons, and the system is applicable to constant intensity telegraphy or telephony transmission as described in Specification 774,471, to the control of guided missiles, and to the identification of friendly or enemy stations. The several radiation elements of the beams may' comprise optical radiation with distinctive spectral characteristics or distinctive planes of polarization; or radio waves having characteristic wavelengths or modulation frequencies.