Patent GB-912883-A (GB)
Title: Improvements in high speed telegraphic or telemetering systems
IPC: G08B26/00
Filed: 1959-02-12
Abstract: 912,883. Electric selective-signalling systems. VALENSI, G. Feb. 12, 1959 [Feb. 13, 1958; Dec. 31, 1958], No. 4947/59. Class 40 (1). [Also in Group XL (b)] In a telegraph transmission system in which each character to be transmitted is represented by a preliminary synchronizing signal sp of short duration t followed by a code signal of longer duration T, the amplitude of which determines the selection of the character for reproduction, the transmitter is arranged to produce a synchronizing pulse of duration t and of amplitude relatively large compared with that of the coded pulses of a train of duration T and representing in a binary code the amplitude of the character selecting signal, and the receiver is arranged to separate the synchronizing signal from the binary code signal which is converted to the corresponding character-selecting amplitude signal and which in conjunction with the synchronizing signal is applied to a cathode-ray tube to control an arrangement to reproduce the desired character. The system may be employed to obtain a printed version of a telegraphic message or, for telemetering systems, to obtain a visual reproduction of indications relating to a number of instruments. In the system shown in Fig. 3, a character to be transmitted is represented by a tape perforation on line 2 corresponding to the preliminary pulse sp and selective perforations in the six lines 3 ... 8 representative of the amplitude designation of the character. The perforated tape 1 is moved continuously in the direction of the arrow v past a scanning system comprising a linear light-source 9 and a set of seven photo-transistors 12 ... 18. The phototransistor 12 is connected via an amplifier 20 to a valve Z1 producing from a pulse sp a pulse sp2 of duration t which is converted by a shaping circuit SF1 to a sine-wave oscillation sp1 fed through a delay device DL to an electronic mixer MX. The outputs from the phototransistors 13 ... 18 are fed to an array of combining resistors 23<SP>11</SP> ... 28<SP>11</SP> having progressively doubled values (R, 2R ... 32R) and to amplifier 22 so that signals sc of different amplitude values corresponding to the various selective combinations of holes are produced. The signals sc are of duration T corresponding to the time interval between successive initial pulses sp1, sp2. Alternate signals sc are fed to gates GA, GB controlled by a timing circuit TC and via holding and coding circuits SHA, CDA, and SHB, CDB to gates GA<SP>1</SP>, GB<SP>1</SP> to provide quantized signals I representative of the amplitude of a signal sc. The code signals I are fed via a valve 12 having a circuit RC of short period to a shaping circuit SF2 providing sine wave oscillations II fed to the mixer MX. The amplitude of the pulses I1 are arranged to be less than that of the pulses sp1, sp2, &c. The output of MX is fed over a telephone line A1, A2 to amplitude discriminating device ST which passes the peaks of the signals sp to a shaping circuit SF3 to produce the pulses sp2, sp<SP>1</SP>2 ... separated by a time T and applied through a delay device DL<SP>1</SP> to the control grid W of a cathode-ray tube CRT. The output from the circuit SF3 is also utilized to open the gate G1 for periods T to allow the received signal I2 to pass through a rectifying circuit R and a slicing circuit SL to produce the shaped impulse train I<SP>1</SP>2 to pass to a frequency recovery circuit FRD controlling a timing circuit TC<SP>1</SP> to open gates G2, G3 to alternate signals. The signals from the gates G2, G3 pass to decoding circuits DCA, DCB and hold circuits SHA<SP>1</SP>, SHB<SP>1</SP> to provide signals sc, sc<SP>1</SP> ... of the corresponding amplitudes which are passed by gates G4, G5 also controlled by circuit TC<SP>1</SP> to the circuit RA and the plates V of the CRT controlling the vertical position of the beam. The fluorescent screen F of the tube is associated with a screen DS having fifty-three columns, each including the fifty-three letters, numerals, signs and symbols which can be transmitted. A lenticulated screen l1 ... l53 corresponding to the character screen DS is associated with lenses L1, L2 to project an image of the selected character on to a slot s of a camera CM enclosing a film f which is stepped for each character by a pulse sp2, sp<SP>1</SP>2 ... fed via a circuit BA to valves 24, 25, charging a capacitor 26. Each pulse derived from the circuit BA is also fed to the horizontal plates H of the CRT so that successive characters are selected from successive vertical columns of the characters on the screen DS. At the end of a line formed by fifty-three characters, negative pulses from valve 25 are no longer fed to a valve 29 which becomes conducting, effecting the discharge of capacitor 28 which applies a voltage to the horizontal plates H so that the beam is restored to an initial position and, in response to the first character signal of a new line, selects a character from the first column of the screen DS. A high voltage normally fed from a source # is cut-off by a gate G6 closed by pulses from a differentiating and reversing circuit in response to the initial and final portions of the pulses sc, sc<SP>1</SP>, ... In a modified printing arrangement, Fig. 3e, the appropriate character on the screen DS is illuminated by the positioning of the beam of CRT on the phosphorescent screen F and projected on to the slit s and paper sheet p of the camera CM, as described in connection with Fig. 3. The signals sp2<SP>1</SP>, sp2<SP>11</SP> ... are delayed at DL<SP>1</SP> so that the intensity of the beam is at a maximum when its vertical position is determined by the central part of the pulses sc, sc<SP>1</SP> ... The paper p which has a coating of zinc oxide in a resin binder including a dye sensitizer, is first made sensitive to visible light by a blanket negative electrostatic charge, and the characters of the screen DS being opaque on a transparent background, a corresponding negative electrostatic latent image is left on the paper sheet. A cylindrical magnet rm is rotated in a tank t containing a mixture of iron powder and particles of a toner of a low melting- point pigmented resin so that as the surface of the magnet passes near the paper p, the toner particles, which in the mixture are positively charged are attracted to the electrostatic latent image and form a corresponding powder image which is heated at hp to form a visible image of the character. A further modification, Fig. 3h (not shown), employs a xerographic printer in which the images of a line of characters are projected on to an axial strip of a rotating cylinder with its surface coated with a photoconductive material and given a negative electrostatic potential so that latent images of the received characters remain. A toner mixture comprising lycopodium powder and a carrier is applied to the cylinder and adheres to the latent electrostatic images on its surface. The cylinder subsequently rotates near a recording sheet carrying an electrostatic charge of opposite sign to that of the toner particles and on which a powder image is formed and is rendered visible by passing the sheet over a heated platen. In a modified telegraphic system, as shown in Figs. 5, 5b, perforations are made above and below transverse lines such as q, q + 1, q+2, on line 1 corresponding to the initial pulse sp and selectively on lines 2 ... 7, if a six-unit code is used to represent the amplitude signal sc. If a five-unit code is employed perforations are not made in the line-2 position. The tape b is fed continuously by a motor mo which also rotates a mirror drum mt so that a short linear light beam is traversed across the tape b. The beam produces from photo-cells ph, ph<SP>1</SP> and amplifiers 21, 22 two pulses of opposite polarity and from elongated photo-cells cp, cp<SP>1</SP> and amplifiers 22, 22<SP>1</SP> a train of pairs of pulses of opposite polarity corresponding to the selective pairs of perforations. The pulses from amplifiers 21, 211 are arranged to have an amplitude substantially greater than those from the amplifiers 22 and 22<SP>1</SP> and all the pulses are arranged to have or simulate a sinusoidal waveform by making the holes in the tape of special shape as indicated by Fig. 5c (not shown). At the receiving end A2 of the transmission line A1A2, the pulse trains are passed to an amplitude-limiting circuit ST and shaping circuit SF3 so that pulses sp2, sp<SP>1</SP>2 ... are derived and passed through delay circuit DC<SP>1</SP> to a circuit dr connected to the elongated cathode K of a CRT Oc. The pulses sp2, sp<SP>1</SP>2 ... are also fed to a thyratron valve th generating a saw-tooth waveform applied to the vertical plates v, v<SP>1</SP> of the tube Oc. In addition the pulses are sp2, sp<SP>1</SP>2 are applied at b, b<SP>1</SP> to effect the movement of the sheet PS for the recording of each character. The code signals defining the amplitude signal for selecting the character are applied through gate G1 opened during the interval between the sp pulses to amplifier R and shaping circuit SL to a frequency recovery circuit FRD controlling a timing circuit TC<SP>1</SP>. Alternate signals are applied via gates G2 and G3, decoding arrangements DCA, DCB and holding circuits SHA<SP>1</SP>, SHB<SP>1</SP> to control the horizontal position of the beam which can be selectively positioned on an electrode member E, Fig. 5e, having a band B carrying the various characters formed by short slots in a 7x5 mosaic corresponding to the shape of the character, the vertical lines of slots being coincident with groups of seven wires connected to terminal points b1 ... b7 on the tube Oc and connected to probes e1 ... e7 terminating near the surface of the recording sheet PS. The signal oc selects the character by controlling the horizontal position of the beam which is arranged to the horizontal extent of the character on the member B,