Patent GB-621615-A (GB)
Title: Method of and means for transmitting signals applicable to telecommunication installations
IPC: H04J3/00
Filed: 1945-10-23
Abstract: 621,615. Multiplex systems. VALENSI, G. Oct. 23, 1945, No. 27963. Convention date, July 16, 1943. [Class 40 (iv)] [Also in Group XL (b)]  In a multi-channel carrier telephone system the numerical impulses and supervisiory signals for all speech channels are transmitted by television technique over one channel which is connected by synchronous distributers at both ends of the line to each of the speech channels in turn for a period sufficient for the transmission of the signals relating thereto. In the system shown in Figs. 1a, 1b, the sending end distributer is an iconoscope I and the receiving end distributer a cathoderay oscillograph having a fluorescent screen OC. The sending and receiving lines LE, LR are coaxial circuits, the channel and group modulators and demodulators MV, DV and MG, DG respectively being fed by oscillators OV, OG synchronized by the master oscillator MO. The signal sending panel PE comprises a group of lamps lp, l<SP>1</SP>-<SP>10</SP>, lf for each speech channel while the receiving panel PR comprises a similar array of photo-electric cells. The sending panel is scanned synchronously with the receiving panel so that the illumination of any lamp results in the operation of the corresponding photo-electric cell. The lamps may be illuminated under control of relays rp, r<SP>1</SP>-<SP>10</SP>, rfby operation of an operator's keyboard or, in the case of tandem calls by a signal repeater which operates the relays. Each of the relay-lamp pairs r<SP>1</SP>, l<SP>1</SP> ... is used to transmit a numerical signal and a service signal, the relay-lamp pair rp, lp serving to send a preliminary signal to indicate the numerical signal. The relay rf and its associated lamp lf are for the purpose of sending an acknowledgement signal of each signal received and are brought into action automatically on the reception of each signal. The depression of the selection key and the key for digit 1 on the keyboard brings up rp and r<SP>1</SP> and the lamps lp and l<SP>1</SP> are illuminated, so that the photoelectric cells cp and c<SP>1</SP> of the panel PR of the receiving exchange are illuminated. The illumination of cp causes the thyratron thpto fire, thereby freeing the normally blocked thyratron th<SP>1</SP>;<SP>1</SP> and blocking the thyratron th<SP>1</SP>,  Since the th<SP>1</SP>,<SP>1</SP> thyratrons correspond to numbering signals and th to service signals, the operation of the selection key serves to predetermine which of the two signals associated with each numerical key is to be effective. At the same time the illumination of c<SP>1</SP> causes th<SP>1</SP>,<SP>1</SP> to fire, whereupon relay r<SP>1</SP>,<SP>1</SP> operates and releases the corresponding impulse train to the called exchange. The scanning is controlled by relaxation oscillators OR, OR<SP>2</SP> synchronized by the master oscillator MO either directly or over the pilot path VP. The output of the generator G which is of rectangular waveform with a period of one second, is fed to the anodes of the thyratrons, the arrangement taking one second to dispose of one signal for each channel. Operation of any of the relays r 1,1 r<SP>1</SP> <SP>2</SP> ... brings up rf to send the acknowledgement signal. Use of 4-unit or 5-unit code. Fig. 2 (not shown) illustrates a modification using a 4-unit code for the transmission of all signals, and the use of a 5-unit code is also described. Known telegraphic apparatus, e.g. keyboards with arhythmic manipulation, may be used for controlling the relays and lamps, provision being made for the locking of the undepressed keys until the acknowledgement signal is received (see Group XL (b)). Alternative methods of scanning. Instead of using cathode-ray tubes, scanning may be performed by the use of mirror wheels (Fig. 3) or reflecting screws (Fig. 3a, not shown). The Fig. 3 modification comprises a Weiller drum RM carrying mirrors equal in number to the number of horizontal rows of lamps in the sending panel PE and arranged so that during revolution all the lamps are scanned, being conjugated in turn with the photo-electric cell CP. For reception, light from a source E passes through a Kerr cell CK and is focused by the optical system so as to scan the receiving panel PR after impinging on the mirror drum, the currents incoming at AO serving to modulate the light beam to vary its intensity as the panel is scanned. The mirror wheel RM driven by a D.C. motor is synchronized by the master oscillator MO. Prevention of operation by parasitic currents. Accidental operation of the r relays by parasitic imputes is avoided either by arranging the lamps corresponding to the same speech channel on different horizontal lines of the panels, or by repeating each signal several times before it becomes effective. The latter method involves the use of the construction of Figs. 6, 7 (see Group XL (b)) comprising a friction clutch operated by synchronizing pulses, a ratchet-and-pawl drive from the receiving relay, and a rack-and-pinion drive to the code bar, which is moved one-third of the distance towards the operative position every time the receiving relay is operated, providing the. clutch is engaged, so that unless the signal is repeated three times while the clutch is engaged it will be ineffective. Alternative transmitters. The arrangement of relays r and lamps l may be replaced by ionic relays in the form of ampoules having a portion of the wall coated with fluorescent material (Fig. 8, not shown). These relays fire under control of the grid and the light from the fluorescent portion is employed for transmission. The modifications of Figs. 9, 10 (not shown) use another method of producing the light for transmission. A code screen (Fig. 9a, not shown) carries the thirty combinations for a five-unit code, each comprising transparent and opaque portions to represent marks and spaces, and is disposed between a light source and a mirror rotatable under control of an operator such that the angle of the mirror determines which of the thirty combinations is conjugated with the mosaic of an iconoscope, to control transmission.