Prediction of Medium-Frequency Skywave Field Strength in North America

Medium-frequency skywave propagation is a very complicated matter. As a result, it has been very difficult to predict the skywave field strength, particularly for propagation paths in North America. The existing method in the FCC Rules and Regulations offers reasonable accuracy only when the sunspot number is low. A more recent method proposed by CCIR Interim Working Party 6/4 works well for other regions of the world but displayed certain limitations when applied to propagation paths in North America. Its treatment of frequency is exactly the opposite to observations made from measurements taken in North America. Its treatment of solar activity is also oversimplified. A new method developed by this author mathematically takes care of the uniqueness of North American paths, consequently, better results have been obtained. This paper presents the derivation of the new method together with a comparative study of the three methods that are now available. Extensive FCC data has been used as a common base.