Development of the Visual-Type Airway Radiobeacon System

Research work on a visual-type radiobeacon system for use on the airways of the United States has been under way at the Bureau of Standards during 1926-1929. As a result of this work a system has been developed which fulfills the requirements for course navigation on the civil airways. A directional transmitter is employed on the ground making possible the use of simple apparatus on board the airplane. A single radio receiver is sufficient to make use of all the radio aids provided. Visual indication is provided by means of a tuned-reed course indicator. The pilot observes the vibration amplitudes of two reeds. On the course the amplitudes are equal. Off the course they are unequal, the reed vibrating with the greater amplitude being on the side to which the airplane has deviated. Two types of beacon transmitters are described, the double-modulation and the triple-modulation. The former is capable of serving either two courses at 180 deg. with each other or four courses at arbitrary angles. The latter serves twelve courses at arbitrary angles and is better adapted for use at airports located at the junction of a large number of airways. Reed indicators for use with the double-modulation and triple-modulation beacons are described. A discussion of the radio receiver and receiving antenna system employed is included. Airplane engine ignition shielding is also discussed. A marker-beacon system has been developed whereby the pilot is given visual indication of his exact position at definite intervals along the route.