Radio broadcast .. (1922-30)

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IO2 RADIO BROADCAST Radio direction finder frame on which telescope is mounted for use in sighting on the radio transmitting station. The scale of degrees is the circular disk just below the hand of the observer to go through such a complicated procedure to learn the direction of sources of light waves because the human eye is itself an almost perfect direction finder for sources of light waves on account of its highly developed sense of sight. We do not have physical senses which enable us to feel or see actually the direction from which waves reach us from a radio transmitting station, so it is necessary to use a device which will give us some effect which can be observed through one of our senses, and this effect must be different when the device used is in the line of the front of the radio wave from what it must be when the device is perpendicular to the front of the wave or in line with the direction in which the wave is carried or transmitted along the surface of the earth. Such a device is found in one of the many types of antennas used for receiving radio signals. When this type of antenna is used with the proper tuning and other receiving apparatus, it changes the energy carried by the radio waves into sound which can be heard by our ears. An antenna which is conveniently used in this way is made by winding a few turns of wire upon a frame a few feet square. The ends of this coil are connected to the rest of the receiving apparatus. When the coil is in the general vicinity of the radio transmitting station it is found that the signals which one hears are louder or weaker, depending upon the position of this coil antenna when turned about a vertical axis. When the coil is parallel to the front of the radio wave, there is little or no response, that is, one hears no radio signals. When the coil is perpendicular to the front of the radio wave, but is turned in the line of direction of transmission of this wave, there is a maximum response, that is, loud signals are heard. Therefore a coil antenna is a direction finder which will enable one to determine the direction of a radio transmitting station which is the source of radio waves. A common form of direction finder for use in receiving from the present day radio telephone broadcasting stations is a coil of about six turns of wire wound on a frame four feet square. All practical uses of the radio direction finder require that it be connected to a sensitive detector and amplifier in order to secure reasonably loud signals. This is necessary because of the small size of antenna which can be conveniently turned around in one direction or another. The principal practical uses of the radio direction finder in radio communication are: (1) Its use on shipboard as an aid to the navigation of the ship.* By its use the captain of the ship may tell the direction to a transmitting station located at a lighthouse. (2) Its use at a radio station along the coast for determining the direction to a ship which *See Bureau of Standards, Scientific Paper No. 428.