An Analysis of Continuous Records of Field Intensity at Broadcast Frequencies

Continuous records of the field intensities of most of the broadcast stations in the United States have been made at the National Bureau of Standards receiving station near Washington, D.C. Typical records of received field intensities from several stations are presented. Maximum field intensities during ten-minute time intervals are analyzed in the following ways to illustrate sky-wave propagation phenomena at broadcast frequencies for distances up to 4000 kilometers. (1) The diurnal variation of the ten-minute maxima is given for several stations. (2a) The variation of the ten-minute maxima is shown with respect to distance for night field intensities. (2b) These variations are also shown for sky waves received during the daytime. Empirical formulas are developed to represent the data of (2a) and (2b). The data are explained in terms of a theory of propagation of waves in the ionosphere. During the past three years graphical records of the field intensity of over three-hundred broadcast stations in the United States and Territories have been made at the National Bureau of Standards receiving station at Meadows, Maryland, near Washington, D.C. The method used for recording the field intensity is described elsewhere. It is the purpose of this paper to report these data and some of the conclusions reached from an analysis of these records.