Radio Broadcast (May-Oct 1922)

RADIO BROADCAST 115 midable than a number of turns of insulated wire wound on a wooden frame a few feet square. This frame takes the place of the usual antenna and the ground connection. Its two leads are brought to the antenna, and the ground binding posts of the receiving set. The loop is used indoors, and must be so mounted that it can be turned about on its vertical axis. When the loop is facing end on toward the desired transmitting station, it receives the signals loudest. Indeed, the loop is the basis of the radio compass, which has proved such a boon to navigators, enabling them to take their bearings from shore stations. The loop is invaluable in radio-phone reception because aside from the sharp tuning qualities of the loop as compared with the usual antenna, it also enables an additional distinction to be made between the desired transmitter and the undesired transmitters by swinging the loop into the best position. The best type of receiving set must be employed in connection with loop antennae. The crystal detector will not do. Unless a very short distance is to be covered, say twenty-five miles or less, a two-stage amplifier must be employed. For greater distances than seventyfive miles, a two-stage radio-frequency amplifier must be used to build up the intercepted wave energy, and a two-stage audio-frequency amplifier may be used in addition to build up the sound strength. The efficiency of radio transmission varies from time to time. One evening a given receiving set will receive loud and clearly from a transmitter four hundred miles distant. Another evening, it will barely receive from a transmitter one hundred miles distant. Therefore, the effective range of a radio receiving set is always based on the distance which it will span under average conditions, and often this range is greatly exceeded for short periods. Broadcasting on Power Lines A DEMONSTRATION was recently given by General George O. Squier, Chief Signal Officer, U. S. A., of the , application of his "wired wireless" or "line radio" system for broadcasting which is bound to have a far reaching effect on the future development of the broadcasting art. General Squier has demonstrated experimentally in his laboratories that it is entirely feasible and practical to transmit high frequency current telephony over power lines, electric light circuits, and for it to be received at any point on the line. A single transmitter connected to the power lines at some suitable point may broadcast over a considerable area and may be received by a large number of people by connecting receivers at various points on the line, the connection being made by a suitable plug in any light socket. The transmitters or receivers are of the usual types now employed for radio telephony and may be connected to the power line in various ways; the preferred arrangement used at present is shown in the following diagram. In this method of connection, the danger of short circuiting the mains is entirely avoided, the condensers between the mains acting as a by-pass for the high frequency currents only, permitting the power current, direct or alternating, but of low frequency, to flow along the POWER. RECEIVER GROUND mains. For the radio currents the two mains are connected in parallel and used as one conductor, the ground being the return conductor. Good results are also obtained by connecting the transmitters and receivers between the mains, suitably protected by condensers to keep the large power current from passing through the radio apparatus, but the arrangement indicated above is more suitable. The advantages of the line radio method of broadcasting as contrasted with space radio broadcasting are many. In the first place, the ether channels used for space radio broadcasting are limited, and even the few wave channels which are available for broadcasting can be more profitably employed for such radio activities where space radio is the only or best