Question

Name the type of waves which are used for the line of sight (LOS) communications. 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 Earth = $6.4 \times {10^6}m$)

Answer 1

- Hint- For LOS communication, very high frequency waves are required. The same waves are used in space satellite communications. A proper height of antenna is required on earth so that the waves may go uninterrupted.

Formula Used:- ${d_m} = \sqrt {2R{h_t}} + \sqrt {2R{h_r}} $ ,where dm is the maximum satisfactory distance for communication, R is radius of earth and $h_t$ and $h_r$ are the heights of the transmitting and receiving antennas.

Complete step-by-step solution -

Space waves are used for this type of communication. They have frequencies greater than 40MHz.
To calculate the maximum distance,
${d_m} = \sqrt {2R{h_t}} + \sqrt {2R{h_r}} $
$
   = \sqrt {2 \times 6.4 \times {{10}^6} \times 20} + \sqrt {2 \times 6.4 \times {{10}^6} \times 45} \\
   = 16000 + 24000 \\
   = 40000m \\
$
= 40 km

Note:- The formula is important in this case. Also, the waves used for different types of communications must be remembered along with their frequencies.