from math import pi,sqrt
#Variable declaration
P_transmit = 25000.0 #Power transmitted by station transmitter (W)
gain_dbi = 29.0 #Gain of array (dBi)
r = 7500e3 #Distance (m)
h = 250e3 #Height (m)
z = 377.0 #Intrinsic impedence of free space (ohm)
#Calculation
gain = 10**(gain_dbi/10) #Gain of array (unitless)
erp = gain*P_transmit #Effective radiated power (W)
p_area = erp/(2*pi*r*h) #power per unit area at distance r (W/m^2)
field_str = sqrt(p_area*z) #Field strength (mV/m)
#Result
print "The effective radiated power is", round(erp,-5),"W"
print "The field strength at the distance r is ",round(field_str,3), "V/m^2"