The Transmission of Pictures

Radio Record, Volume II, Issue 39, 12 April 1929, Page 32

The Transmission of Pictures

New Wireless Triumph

*‘s"I\HE day when the transmission and reception of telegraph messages in facsimile instead of by the Morse system will become the normal procedure has been brought appreciably nearer," states the "Morning Post," England. Recently a number of pictures and hand-written messages were flashed across the Atlantic on a short-wave beam circuit, in operation between New York and Somerset. The pictures, which included cartoons and views of American buildings, reached England almost simultaneously with their transmission from America. They were received with astonishing ease and quickness. The system is remarkable for its clarity. A "facsimile" .service is in preparation which may in time make it the normal procedure for telegrams to be received in-the actual handwriting of the sender-an advantage evident in the transmission of elaborate columns of figures, where absolute accuracy is assured. The system at present employed enables two images, each eight inches by ten inches, to be received from America in less than 20 minutes, and may actually reduce costs as compared with present methods. In commercial operations, one of the channels could be used for ordinary telegrams, and the other reserved for urgent messages. The Method, "THE telegram or drawing to be transmitted is placed over a cylinder and is traversed by a point of light. This light is provided by a motor headlamp bulb which is focussed into a spot, and this is rotated so that the light passes through 2 slot in the metal eylinder over which the message is slowly drawn. Every part of the image is, therefore, illuminated by the spot of light. at a speed which is very accurately controlled. A photo-electric cell is so arranged that the reflection of the light. which varies in intensity with the degree of whiteness or darkness of the image, falls upon it, and electric currents are therefore produced. These are magnified and radiated by the "beam" transmitter. The receiving gear comprises the usual receiver and apparatus for reversing the process carried out at the transmitter. A sheet of photographic paper is placed over the receiving cylinder and is held down by a cover of celluloid through which the spot of light may be observed. As at the transmitter, this spot of light rotates and passes through a slot in the cylinder over which the sensitised paper is drawn, and it is controlled by a Lerr cell. ‘This operates as a light shutter, which allows a spot of light to fall on the paper only when a current is passed through the cell, and is therefore one one of the vital parts of the apparatus. The light is normally cut off from the paper, but when a current is received the cell operates and allows the light to fall on the paper, with the result that the light and dark portions of the message are reproduced at the receiver.

As the image at. the transmitter ig traversed by the light, so the light at the receiver is tracing out a copy with complete accuracy, and except for bad atmospherics or other disturbances the copy will be as clear as the original. The copy may be in the form of a photographic positive or negative, and is quickly fixed. . An advantage of the system is that the receiving machine may be located many miles from the receiving station, and this is equally true of the trazjsmitter, although at the moment ciently good telephone lines are not normally available at the American end. Errors through mistakes on the part of operators are ayoided by this system. and when greater speeds are possible there may be a great saving in the cost of telegraphic transmissions. Years of Experiment. LMOST ever since the inception of the telegraph, the problem of picture transmission has fascinated electrical engineers. As early as 1842 Alexander Bain invented a highly ingenious system, and many others have followed more or less in his footsteps with widely varying results. The first telegraphic picture service opened to the public, however, was that which has been in commercial operation between Radio House, the Marconij,. main telegraph office in London, and New York since May, 1926. Some hundreds of news pictures, cartoons, fashion plates, signatures, cheques, and plans have been transmitted commercially across the Atlantic by this system. During the recent facsimile tests, Bryan Davis, the young son of the English engineer in charge of the American end of the experiments, was able to send a picture of himself in a new hat, with a New Year message, to his grandparents at Chelmsford. He also persuaded the engineers to transmit favourite pages of his picturebooks and adventure stories across the Atlantic for test transmissions, and the engineers say that, with their simple pictures and clear type, these make ideal facsimilegrams,