The Ground wave Attenuation factor A. The relation between numerical distance p and phase constants b is shown in Fig. 11.7. The numerical distance p depends upon the frequency and the ground constants and the actual distance to the transmitter. It is proportional to the distance and the square of the frequency and varies almost inversely with the ground conductivity. The phase constant b is a measure of the power-factor angle of the earth. The attenuation factor A may be represented by following empirical formula