A microwave transmitter has an output of 10 W and is separated from the extreme receiver by a distance of 50 km. Suppose that this transmitter is used in a radio communications system, in which the transmitting and receiving antennas are parabolas, each one with a gain of 45 db and an antenna efficiency of 75%.

a) Determine at what frequency the transmission system should operate, if the allowable losses in free space are FLS = 138.5 db.

b) Determine the power at the receiver (dbm), if the loss in the transmission line on the receiver side is 4 db.

c) Determine the Directivity of the parabolic antennas in db.