An obsolete radio directional aid that could be received by a normal wireless telegraph (W/T) receiver. A ground station transmitted repeatedly the Morse letters A or N over four sectors; the adjacent sectors were different. The overlapping of the signals created four beams, or legs, in which a continuous note could be heard, thus providing a track guide. The beams were not usually at 90° but often adjusted to provide a track along an airway. At points along the beams, fan markers were placed to provide an indication of distance from the station. Over the actual transmitter, a marker beacon sending repeated Z signals could be heard.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved