Radio Broadcast (May-Oct 1925)

A New Method of Transmitting Pictures by Wire or Radio 21 time increase the capacities of their present stations. HOW PICTURES SOLND IF YOU should ever listen to radio signals that are serving to transmit photographs, you will hear a buzz of constant pitch but of varying intensity. The variations in intensity seem to repeat every second, or probably oftener, but each repetition will be slightly different from the previous buzz. Each impulse, that goes to make up the buzz, represents the light coming from a tiny area on the picture being transmitted. Every one knows that newspaper prints are made up of thousands of tiny dots. In light places on the pictures, these dots are very small. The dark portions are made up of dots so large they form together to make a solid black mass. When transmitting any photograph, a dot is sent with each electrical impulse, but these impulses occur so rapidly that they appear as a buzz when one hears them on the radio. Rows of dots are sent in rapid succession; this explains the repetition of the signal intensities at short intervals. It is not necessary to split the photograph up into tin}' dots before transmitting, for this is automatically done by the electrical apparatus in the photograph transmitter. At the receiving station, the electrical impulses are transferred on a suitable paper back into dots and these dots are arranged exactly as they are on the original picture. To do this, both transmitting and receiving apparatus must operate at exactly the same speed, that is to say, they must be synchronized. The technical problems involved in synchronizing have been some of the most important of the many difficult ones in developing the transmitting apparatus. A picture that is to be transmitted across the Atlantic by the Radio Corporation of America's system, or from one city to another over the Bell System lines, is first printed on a transparent film. This process is rather simple and does not require much time. Nevertheless, such a procedure would involve undesirable complications for constant and regular commercial service. Both the Telepix and Belin systems call for especial types of negatives peculiar to the transmitting methods employed. The making of such negatives requires a little more time than do the prints used on the Radio Corporation and American Telephone and Telegraph Company i Radio Broadcast Photograph THE RADIO BROADCAST LABORATORY Showing the antenna and counterpoise system. Two masts eighty-five feet high support the two cage antennas. The longer antenna has a spread of 154 feet. The laboratory where Mr. Cooley did much of the development work on his photograph transmission system is located in the white cabin between the two masts. The buildings of Doubleday, Page & Company are in the background