Question

Distinguish between ‘sky waves’ and ‘space waves’ modes of propagation in communication system. 

(a) Why is sky wave mode propagation restricted to frequencies upto 40MHz? 

(b) Give two examples where space wave mode of propagation is used.

Answer 1

Sky wave — Sky wave propagation can be achieved by ionospheric reflection of radio waves back towards the earth, in the frequency range from few MHz up to 30 to 40MHz. Space wave — In this mode of propagation, radio wave travels in a straight line from transmitting antenna to the receiving antenna. 

(a) Sky wave propagation is restricted to frequency upto 40MHz, because the radio waves of frequencies more than 40MHz penetrates into the ionosphere. 

(b) Space wave propagation (LOS) is used in 

(i) Television broadcast 

(ii) Microwave link 

(iii) Satellite communication