Microwave Transmission:

Using space as transmission medium, microwave emanates from an origination point on earth, such as telephone exchange, where many individual messages have been concentrated. Because the microwave beam travels in a straight line, it is advantageous to place microwave towers on hills or mountains to minimise interference from land mass. Usually, towers are placed between 25 to 30 miles apart to remain in sight of each other ('line-of-sight'). Microwave transmission can carry 600 to 1800 voice channels. Advantages of microwave transmission include lower cost than coaxial cable, where right-of-way must be obtained and higher costs are incurred when the physical cable is laid over long distances. As with other systems that transmit through free space the signals are subject to fading caused by absorption and scattering from moisture and precipitation in the air. In other words, atmospheric interference is greater and rain can cause. severe transmission problems. 

The great advantage is that the microwave transmission is a broad band facility able to carry several thousand channels. It is suitable for bulk transmission data over long distances.