direct wave[də¦rekt ′wāv]
A radio wave that is propagated directly through space from transmitter to receiver without being refracted by the ionosphere.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
An electromagnetic wave that travels directly from a transmitting antenna to the receiving antenna along a straight line. Direct waves are responsible for part, but not all, of the signal propagation between two antennae when a sight line connecting the antennae lies above the ground. The surface (ground) wave and the reflected wave also contribute to the overall signal at the receiving antenna. Also called a line-of-sight wave or a space wave, it is prevalent in frequencies above 30 MHz.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved