In a line of sight radio communication, a distance of about 50 km is kept between the transmitting and receiving antennas. If the height of the receiving antenna is 70m, then the minimum height of the transmitting antenna should be :
(Radius of the Earth = 6.4 × 10⁶ m).

The wavelength of the carrier waves in a modern optical fiber communication network is close to :

To double the covering range of a TV transmittion tower, its height should be multiplied by :

A 100 V carrier wave is made to vary between 160 V and 40 V by a modulating signal. What is the modulation index ?