Patent GB-263919-A (GB)
Title: Improvements in picture transmission systems
IPC: H04N1/327
Filed: 1925-10-02
Abstract: 263,919. Western-Electric Co., Ltd., (Bell Telephone Laboratories, Inc.). Oct. 2, 1925. Copying- telegraphs; synchronous movements.-In a copying-telegraph system employing two carrier waves of different frequencies which are modulated, one in accordance with the tone values of elemental areas of the picture or the like to be transmitted, and the other by synchronizing current, means are provided for signalling over the circuit by a current of a third frequency, in order to facilitate the preliminary tests and adjustments and the control of the transmission. The arrangement includes switches for connect- .ing telephone sets to, and simultaneously disconnecting the picture transmission devices from, the circuit. The gereral operation of the system is similar to that described in Specification 242,694. Picture exploring device at transmitter, Fig. 1. A transparency of the picture is mounted on a drum 10 on a shaft 11 carried by a frame 15 slidable in guides on a support 16, and the shaft 11 is driven through gearing 19, 20 from a shaft 17 driven through a magneticallycontrolled clutch from the shaft 22 of a phonic motor 12 and threaded to impart sliding movement to the frame 15. The shaft 22 drives through gearing 23, 24 a crown wheel 26 loose on the shaft 17, and the wheel is clutched to its shaft by the engagement with the crown, under the action of a spring 28, of a toothed sector 27 pivoted to the shaft. The sector is normally held disengaged by a spring-controlled stop arm 30 which is operated to release the sector by energizing a magnet 31, and the arm falls into position to disengage the sector when the magnet is de-energized. The circuit of the magnet 31 includes switches 48, 49, 52, and stopping switches 50, 51 controlled by the frame 15. The motor 12 is driven by current supplied through the switch 49 and controlled by contacts 39, 40 on a fork 14 driven by a magnet 34 which is energized through switches 49, 50, and 51. Additional arms are provided on the switches 50, 51 serving to open the circuit of the magnet 34 in the event of the frame 15 moving in the wrong direction due to the operator's failure to reverse the motor after a transmission. An image of an aperture in a screen 70, illuminated by lamp 69, is projected by a lens 71 on successive elemental areas of the picture, and the tone values of these areas thus determine the amounts of light incident on the cathode 66 of a photoelectric cell 64 within the drum. Production and modulation of the picture current carrier wave. The wave is produced by a valve 150, Fig. 2, with a grid battery 159, and with a plate battery 152 and a choke coil 153. The feed back circuit includes a resistance 156 and a transformer 157 with a condenser 158 connected across the transformer primary, and this condenser is adjustable for determining the frequency in the output circuit which includes a resistance 154 and a potentiometer 155. A condenser 161 prevents current from battery 152 from affecting transformer 157. The output current is impressed on the input circuit of the modulator PM through a transformer 160, a switch 163, and a transformer 140. The circuit of the photoelectric cell 64 includes the leads 72, 73, a source of potential 103, a double-throw switch 100, and a resistance 104, and the resulting picture current is amplified by the device PCA before being impressed on the modulator PM. The source 103 includes three adjustable sections 110, 111, 112. Each of the sections 110, 111 comprises a series of battery steps with their terminals connected to the contact studs of regulating switches 113, 114, each provided with parallel connected by a resistance 117 or 118 to enable the regulation to be effected without opening the main circuit or short-circuiting an part of the batteries. The section 112 comprises a potentiometer 115 in series with the battery and a resistance 116. The grid circuit of the first valve 105 of the amplifier PCA includes the resistance 104 and a resistance 110<1> which is also in the filament-heating circuit. and the plate circuit includes a battery 120, a resistance 121, and an ammeter 122. The grid circuit of the second valve 106 includes part of the battery 120 and a biassing potentiometer 123, and the plate circuit includes a battery 127, a resistance 128, and an ammeter 129. The grid circuit of the valve 131 of the modulator PM includes a resistance 141 connected across the secondary of the transformer 140, a biassing potentiometer 132, and a switch 135 for adding or removing the potential of a battery 134. The plate circuit cf the valve 131 includes a battery 144, an ammeter 142, and the primary of a transformer 143 of which the secondary is connected through the switch 163, or switch 200, Fig. 3, and a filter 166 to leads 184, 185. Production and modulation of the synchronizing carrier wave. The wave is produced by a valve 170. Fig. 2, with circuit connections similar to those of the valve 150. The output circuit includes a resistance 175 and the primary of a transformer 176 of which the secondary is connected through a modulator circuit 174 and a filter 183 to the leads 184, 185. The modulation is produced by a contact 33, Fig. 1, on the fork 14 through leads 53, 54, and a switch key 252, Fig. 3. Amplification of the modulated carrier waves and transmission to line. The leads 184. 185 are connected through a potentiometer 210, Fig. 3, and a transformer 209 to the grid circuit of an amplifying valve 211 of which the plate circuit is connected through a transformer 212, switches 230, 232, 233, and 234, and a transformer 243 to the line conductors 322, 323. Amplifying, filtering, and detecting arrangements at receiving station. The receiving end of the line conductors 322, 323 is connected through a transformer 300, Fig. 4, to an amplifier RA, the upper half of the secondary of the transformer being connected through a switch 315 to the amplifier, and the lower half being available for a signalling current in the opposite direction. An adjustable resistance 301 and an adjustable condenser 302 are arranged in parallel in the connection to the mid-point of the secondary for dividing correctly the incoming and outgoing currents. The amplifier RA comprises a valve 318 of which the input circuit includes a potentiometer 320 and a transformer 319, and the output circuit includes a transformer 321. The secondary of this transformer is connected in parallel, as shown in Fig. 5, through a filter 400, a potentiometer 404, and a transformer 405 to the input circuit of an amplifying valve 403, and through a filter 401, a potentiometer 432, and a transformer 431 to the input circuit of an amplifying valve 430, the filters 400. 401 being similar to the filters 166, 183, Fig. 2, respectively. The output circuit of the valve 403 is connected through a transformer 411 to the input circuit of an amplifying valve 410 which is adapted to function alternatively as a detector, for use in starting the rotation of the drum 554, Fig. 6, carrying the sensitized reproducing surface, upon energizing a relay 45 by operation of a switch 313, Fig. 4, or closure of the left-hand contact of a relay 501, Fig. 6. When the valve 410 is functioning as an amplifier, the grid is polarized by a battery 416 through a contact 419 of the relay 415, and, when functioning as a detector, the grid is polarized by a stronger battery 418 which is substituted for the battery 416 by the movement of the relay armature from contact 419 to contact 424. The synchronizing current amplified by the valve 430 is delivered through a transformer 433 to the grid circuit of a detector valve 434. Picture reconstituting device, Fig. 6. Rotary and axial movements are imparted to the drum 554 from a phonic motor 533 through mechanism similar to that for driving the drum 10, Fig. 1. the motor being driven by current through contacts 553, 554. closed by a fork 523. To maintain this fork in synchronism with the fork 14. Fig. 1, the energizing of its driving magnet 522. is, in the upper position of a switch 526, controlled by the vibration of the armature of a relay 508 energized by the output current from the valve 434, Fig. 5. This current passes through the primary of a transformer 509 and the main winding of the relay, an accelerating winding is energized by current induced in the secondary of the transformer, and a third winding is energized by a biasing current from a battery 406, Fig. 5, through an adjustable resistance 407. With the valve 410 functioning as an amplifier its plate circuit includes a contact 423 of the relay 415 and the primary of a transformer 422 of which the secondary is connected through a contact 309 of the switch 303, Fig. 4, to a string 558 mounted in a strong magnetic field and vibratable by the current to control the amount of light from a lamp 560 incident on the sensitized surface on the drum 554. When the valve 410 is functioning as a detector its plate circuit includes the primary of a transformer 505, Fig. 6, and a winding of the relay 501, the secondary being in the circuit of an accelerating winding of the relay. A biasing winding of the relay is energized from the battery 406. Interruption of the picture current carrier wave due to operation of the switch 52, Fig. 1, thus causes the armature of the relay 501 to engage its righthand contact. The circuit of the clutch magnet 547 is thereby closed for starting the drum 554 simultaneously with the drum 10, and the relay 415 is de-energized to enable the valve 410 to function again as an amplifier. Signalling from receiving to transmitting station. The receiving operator, by actuating a key 303, Fig. 4, closes a contact 306 to supply current through an interrupter 304 operating at the signalling frequency. The interrupted current passes through a filter 305 and the contact 308 of the key 303 to the lower half of t