What type,of wave is used for LOS [Line of Sight Model]? What is the range of frequency for this- type of wave?

Name the type of wave which are used for line of slight (LOS) communication. What is the range of their frequencies? A transmitting antenna at the top of a tower has a hight 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 xx 10^(6) m)

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