RECOMMENDATION ITU-R P.684-1 - PREDICTION OF FIELD STRENGTH AT FREQUENCIES BELOW ABOUT 500 kHz 1 Introduction 2 "Wave-hop" propagation theory 2.1 General description 2.2 Calculating the ray-path field strength 3 Calculating field strength by waveguide modes: full wave solution 3.1 The ionospheric reflection matrix R(?) 3.2 The ground reflection matrix, d (?) 3.3 The mode finding method ("MODESRCH") 4 Calculation of field strength 4.1 Required parameters 4.2 WKB and horizontally homogeneous mode sums 4.3 Mode sums using mode conversion 4.4 Ionospheric parameters 4.5 Geomagnetic and geophysical parameters 5 Discussion ANNEX 1 - Example of a complete calculation of field in amplitude and phase using the wave-hop method of § 2 ANNEX 2 - Accuracy of the methods ANNEX 3 - Some example calculations using the waveguide mode method