Short distance night time sky wave field strength at mediun frequency band

Abstract

A theoretical prediction method of night time sky wave field strengths of medium frequencies $\mbox{\underline{at}$ $\mbox{\underline{short}$ $\mbox{\underline{distances}$ (for example, within 1200 Km) is presented. At long distances, rays reflected from the ionospheric E layer are accounted only, because the rays penetrating E layer and reflected from the F layer experiences more attenuation in the ionosphere than the former. At short distances, however, the latter may not be neglected, since within the skip distance there is no rays reflected from the E layer at all. Therefore the latter is accounted here for the field strength. For the comparison of the calculated results with the measured data, horizontal component of the magnetic field is calculated, since a vertical loop antenna is used for the measurement. At long distances, the horizontal mode is usually neglected, since a multiplying factor sin Ψ becomes negligible, where Ψ is the elevation angle of the ray. At short distances, however, this component may not be neglected, since the elevation angle Ψ becomes large. This component is accounted here for the field strength. Calculations for the field strength are compared with the measurements (annual averages of the median values) of field from the 8 transmitting stations located in Japan. A computer program is also developed to calculate and plot sky wave field strength received by the receiver versus distance.