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This paper describes and evaluates the various factors involved in selecting an all-weather, general-purpose, type of navigation system for the radio guidance of civil and military aircraft of all types at long distances from ground-based transmitters. An analysis is made of the factors which affect the range, accuracy, reliability, cost, suitability, and operational utilization of available and proposed radio navigational aids for long-range operation in the light of the most recent investigations and requirements of the Air Coordinating Committee and the International Civil Aviation Organization (ICAO). Considerations affecting the Â¿optimumÂ¿ choice of frequencies are presented based upon the most current operational information of radio wave propagation. An Â¿optimumÂ¿ frequency of 60 kc is selected, based on minimum transmitter power requirements. A brief description is given of the principles involved in several representative continuous wave and pulse types of radial, circular, and hyperbolic position-fixing aids and a comparison is made of pertinent operational and technical characteristics leading to the choice of a possible general-purpose system for civil and military applications. Consideration is given to the possible improvement in the tolerable signal-to-noise ratio, and consequent range extension, of these systems by the application of cross-correlation, coherent, or synchronous detection techniques. Based upon the above criteria, an all-weather, single-site, combined radial and circular system, designated Navarho, is selected as possessing the greatest promise of fulfilling most of the requirements for a general-purpose, ground-referenced system, yielding information automatically, instantaneously, and directly to the pilot.