Patent GB-288234-A (GB)
IPC: H04N5/16
Filed: 1928-01-11
Abstract: 288,234. Electrical Research Products, Inc., (Assignees of Ives, H. E., and Gray, F.). April 6, 1927, [Convention date]. Television. - In a television apparatus designed particularly for transmitting images derived from a moving kinematographic film the direct and low frequency components of the usual currents are suppressed at the transmitter and restored manually at the receiver, the spirally arranged apertures on the scanning disc are adjustably positioned and set so that their paths overlap, and the received image is reconstructed by scanning a neon lamp having a luminous surface larger than the field of view. At the transmitter a magnified image of the intermittently moving kinematograph film is projected upon the photoelectric cell through a scanning disc and an aperture which masks off undesired parts of the image. At the receiver a similar aperture masks part of the large illuminated surface of a glow discharge tube controlled by the received signals. Scanning discs.-The scanning discs contain spirally arranged apertures which overlap slightly. The amount of overlap is so gauged as to reduce inequalities in exposure to a minimum, so as to obviate a line structure in the reproduced picture thus circular apertures may have diameters greater by a quarter than the radial spacing, or square apertures moving diagonally may have their diagonals double the radial spacing, or the apertures may be made up of squares with overlapping triangles. The apertures may be punched either in a disc of thin material or in thin adjustable circular plates 320, Fig. 8, attached to the scanning disc 302 by screws 321 which pass through large holes in the plates. A sector of the scanning disc covering 45‹ is left free of holes to allow for the time during which the film is being moved step-bystep. Thermionic valve circuits.-At the transmitting station the photo-electric cell 202, Fig. 4, is coupled to the first valve of a multistage amplifier across a resistance 204 which is small enough in relation to internal capacity of the valve to give a small time constant in view of the presence of high frequency components of the signals. In order to prevent excessive grid bias from building up in the later stages of the amplifier in consequence of slow changes in the e.m.f. of the batteries in the earlier stages, the resistancecapacity couplings 207, 208 are so calculated as to cut off not only direct current but also lowfrequency alternating components below 10 cycles. At the receiver the input potentiometer 262 and grid bias 268 are so adjusted as to ensure that the operating point of the valve 265 shall move symmetrically within the straight part of the characteristic and that the output voltage shall not fall below the critical voltage of the lamp 310 upon the luminous surface of which the picture is viewed through the scanning disc. The amplifiers are protected against electric magnetic and mechanical disturbances. Synchronous movements.-At the transmitter the kinematograph motor 118 is driven synchronously with the television motor by means shown in Fig. 3. The motor 118 is short circuited through a resistance 166 during half the rotation of the commutator 160 (connecting brushes 163, 164) and half that of the commutator 170 (connecting brushes 173, 174). When these short-circuit periods coincide without overlap the total short-circuit period is a minimum and the motor 118 runs at its maximum speed, but the resistance 176 is adjusted so that this speed is slightly too fast in relation to the speed of the television motor and commutator 160. The half-rings of the commutators therefore lose phase and the total short-circuit period lengthens itself, and the speed is reduced till synchronism is attained. At the receiving apparatus the device for adjusting phase comprises a worm-gear 307, 309, Fig. 5, whereby the common exterior frames of the driving motor 303 and synchronizing motor 304 may be rotated bodily. Synchronism indicatnrs. - At the transmitter the phase relation between kinematograph and television apparatus is indicated bv a stroboscopic device comprising a lamp 177, Fig. 3, which is intermittently illuminated under the control of the commutator 160 associated with the television transmitter, the commutator ring 172 associated with the kinematograph carries a mark 179 and the apparent position of this under the intermittent illumination of the lamp 177 is compared with the position of a fixed mark 178.