Basic Radio is a free introductory textbook on electronics based on tubes. See the editorial for more information....


Author: J.B. Hoag

Above the beacon transmitters (of the type which suppress the sky-wave) there is a " cone of silence." This may be used by the pilot to inform him that he is passing over the station. It is not infallible, because the silence might also be due to a breakdown of the receiver or of the transmitter.

Radio markers are sometimes used. They consist of narrow pencils of radio waves transmitted vertically at 75 MHz (wavelength of 4 meters). These are about 1 mile wide at 1 mile up. Near an airport there is an outer marker, about 5 miles out, and near the edge of the field there is an inner marker.

Last Update: 2009-11-01