Microwave Transmission
Microwave transmission also requires line of sight in order to work properly. In order to allow two way communications two frequencies are used. However, this does not mean that there has to be two antennas because the frequencies can be dealt with by one antenna at both ends.
The distance covered by microwave signals is based upon the height of the antenna. In order to increase this coverage each antenna has a built-in repeater that regenerates the signal before passing it on to the next antenna in line. The placement of the antenna to do this is approximately 25 miles.
The main drawback of microwave signals is that they can be affected by weather, especially rain.
Click on this link to review the wikipedia resource on microwave transmission.
