Question: Q. 10. (i) What is line of sight (LOS) communication? What is the range of their frequencies?
(ii) A transmitting antenna at the top of a tower has a height of $20 \mathrm{~m}$ and the height of the receiving antenna is $45 \mathrm{~m}$. Calculate the maximum distance between them for satisfactory communication in LOS mode. $\left(\right.$ Radius of the Earth $=6.4 \times 10^{6} \mathrm{~m}$ )
U] [O.D. I, II, III, 2013]
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Solution:
Ans. Space waves are used for the line of sight (LOS) communication.
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The range of their frequencies is $40 \mathrm{MHz}$ and above.
We have, height of transmitting antenna, $h_{T}=20 \mathrm{~m}$ and height of receiving antenna, $h_{R}=45 \mathrm{~m}$.
Then, maximum distance between the two antennas,
$$ \begin{aligned} & d_{M}=\sqrt{2 h_{T} R}+\sqrt{2 h_{R} R} \ & d_{M}=\sqrt{2 \times 20 \times 6.4 \times 10^{6}} \end{aligned} $$
$\sqrt{2 \times 45 \times 6.4 \times 10^{6}}$
$=20 \times 8 \times 100+8 \times 100 \times 30$
$=8 \times 100(20+30)$
$=40000 \mathrm{~m}=40 \mathrm{~km}$
