The role of the satellites, in ‘ line of sight ’ communication mode, can be regarded as similar to the role of a

The atmospheric region which acts as ‘ radio mirror ’ is

Thickest layer of the ionosphere is

Locus of points at which direct rays from the antenna are tangential to the earth surface is called as,

The atmospheric layer which reflects low-frequency waves and absorbs medium-frequency waves is,

The phenomenon in optics, that is similar to the phenomenon of ionospheric reflection of radio waves, (by the ionosphere) is the phenomenon of

The height of a T.V. tower is 180 m. The distance up to which the transmission can be made from this tower is (nearly) if the radius of earth is $6.4\times 10^{6}m\mathrm{.}6.4\backslash times10^6\; m.$

The percentage, by which the transmission range of a T.V. tower, would be affected, when the height of the tower is increased by 21% is (nearly).

It is known that the height of a transmission antenna should preferably be of the order. The length of antenna at a place is 0.75 m. Its optimum transmission frequency would be (nearly)

If an audio signal were to be transmitted directly over a long distance, the minimum size of transmitting antenna would be of the order of