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 20m and the height of the receiving antenna is 45m. Calculate the maximum distance between them for satisfactory communication in LOS mode. (Radius of the Earth `= 6.4 xx 10^(6)` m)

Explanation

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_(T) = 20m` and
height of receiving antenna, `" "h_(R) = 45 m`.
Then, maximum distance between the two antennas,
`dm = sqrt(2Rh_(T))+sqrt(2Rh_(R))`
`dm = sqrt(2 xx 6.4 xx 10^(6) xx 20)+sqrt(2 xx 6.4 xx 10^(6) xx 4.5)`
`" "=2 xx 8 xx 10^(3) + 3 xx 8 xx 10^(3) = 40 km`.
Thus, the maximum distance between the antennas is 40 km.