The microwave distance-measuring device (fig. 12-23) is an electronic instrument that transmits precisely controlled RADIO WAVES between two units. The waves are compared and electronically changed into a visually readable form from which the distance between the units can be computed.

As shown in figure 12-24, the unit that originates and transmits the modulated radio waves is called the master. The unit at the opposite end of the line from the master is known as the remote. The two are identical instruments, each being adaptable to use as either master or remote.

At the remote unit, the original transmission is received, interpreted, and put on a new

carrier. This new modulation is amplified and retransmitted to the master. The master analyzes the new transmission and translates it into a trace on a cathode ray tube that can be read visually. The trace information is converted into a distance based on the velocity of the radio waves. Because this velocity is affected by atmospheric conditions, corrections for temperature and barometric pressure are applied according to instructions.

Each instrument is equipped with a shortwave telephone set. By this means, the person at each instrument can maintain communication with the other. Details of the method of operating the system must be learned from the manufacturers instructions.