Question

Name the type of waves which are used for line of sight (LOS) communication. What is the range of their frequencies ?
A transmitting antenna at the top of a tower has a height of 20 m and the height of the receiving antenna is 45 m. Calculate the maximum distance between them for satisfactory communication in LOS mode. (Radius of the Earth $=6.4\times {10}^6$m)

Answer 1

Space waves are used for the line of sight (LOS) communication.
The range of their frequencies is 40 MHz and above.
We have height of transmitting antenna, $h_r$ = 20 m and height of receiving antenna or height of tower, $h_R$ = 45 m
Then, maximum distance between the two antennas,
$d_{max}=\sqrt{2R{h}_T}+\sqrt{2R{h}_R}$
Where R is radius of earth
$d_{max}=\sqrt{2\times 6.4\times {10}^6\times 20}+\sqrt{2\times 6.4\times {10}^6\times 45}$
$=2\times 8\times {10}^3+3\times 8\times {10}^3$
$=40km$.
Thus, the maximum distance between the antennas is 40 km.