Ionospheric scatter communication

VHF propagation by means of ionospheric scatter has been under intensive investigation at the National Bureau of Standards since its discovery in early 1951. The main characteristics of this mode of propagation are now well known and are reviewed. Particular emphasis is placed on practical engineering considerations, such as spaced antenna diversity requirements, choice of polarizations and antennas, and antenna siting. Results are given for such matters as the optimum range of distances and optimum range of frequencies for practical communication. A complete two-way communication system, extending in three stages from Main to Northern Greenland, has been built for the United States Air Force. This system, which provides four radioteletype channels continuously, has been in operation for more than a year and performs entirely satisfactorily from the viewpoint of propagation for considerably better than ninety-nine per cent of the time on the two northern links.