Name the type of waves which are used for line of sight (LOS) communications. What is the range of their frequencies?

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, hT = 20m and height of receiving antenna, height of tower hR = 45m. Then, maximum distance between the two antennas dm = √(2RhT) + √(2RhR) = √(2 × 6.4 × 106 × 20) + √(2 × 6.4 × 106 × 45) = 2 × 8 × 103 + 3 × 8 × 103 = 40km. Thus, the maximum distance between the antennas is 40 km.