communication-systems Question 20
Question: Q. 8. What is space wave propagation ? State the factors which limit its range of propagation. Derive an expression for the maximum line of sight distance between two antennas for space wave propagation.
U] [2016; OD, North Set]
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Solution:
Ans. Space Wave Propagation :
The mode of propagation in which radio waves travel, along a straight line, from the transmitting to the receiving antenna.
Limiting Factors :
(i) Curvature of the earth
(ii) Insufficient height of the receiving antenna (Award this $1 / 2$ mark if the student writes any one of these two factors)
Derivation :
From the figure, we have
$$ \begin{array}{rlrl} & & (R+h)^{2} & =R^{2}+d^{2} \ \text { Or } & 2 R h & \cong d^{2}\left(\text { as } h^{2}«2 R h\right) \ & \therefore & d & =\sqrt{2 R h} \end{array} $$
For a transmitting antenna of height $\mathrm{h}{\mathrm{T}}$, and receiving antenna of height $h{R}$, the maximum line of sight distance becomes
$\therefore$
$$ d_{\mathrm{M}}=\sqrt{2 R h_{T}}+\sqrt{2 R h_{R}} $$
[Note: Give 1 mark if the student writes the expression of $d_{M}$ ]
[CBSE Marking Scheme, 2016]
