communication-systems Question 21
Question: Q. 9. Give (brief) reasons for the following :
(i) We use the ‘sky wave mode of propagation, of electromagnetic wayes, only for frequencies up to 30 to $40 \mathrm{MHz}$.
(ii) The LOS (Line of sight) communication via space waves base (fairly) limited range.
(iii) A mobile phone user gets an ‘uninterrupted link to talk’ while walking.
U] [Foreign, 2016]
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Solution:
Ans. (i) The ionosphere can act as a ‘reflector’ only for $E M$ waves of frequencies up to 30 to $40 \mathrm{MHz}$. Higher frequency $E M$ waves penetrate the ionosphere and escape.
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(ii) The range is (fairly) limited because the EM waves loose energy (fairly rapidly) when they glide over the surface of the earth.
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(iii) This is because of the presence of a network of base stations/cells which keep on passing the signals from one base station/cell to the other.
