PURPOSE AND FUNCTION The Bird WATTCHER® RF monitor is a continuous service equipment designed for the protection and performance observation of radio frequency transmission systems. The Control and Alarm System operates with high reliability electromechanical components working on simple dc and low voltage ac circuits without the use of vacuum tubes or high impedance balanced circuitry. It is designed for use on RF power levels from 1 Watt to 250 kilowatt, and a frequency range from 0.45 to 2400 MHz. In use, a two-element THRULINE® line section will be required. The THRU LI NE® RF line section will depend upon the type of coaxial transmission line being used in the system. Two plug-in elements are selected to cover the power levels and frequency ranges used. The function of the element is to detect (sense) the forward or reflected RF power in the line section at any give time. The direction in which the "arrow", on the Element cap, is oriented indicates the direction in which it is sensing the RF power flow in the system. The dc outputs of these detectors are fed respectively to the two panel meters, which indicate directly the forward and the reverse RF energies (incident or reflected power). The reflected power meter has a relay contact incorporated into it, and if the set level is reached, visual and audible alarms will function; and when so wired, external warning devices and transmitter disabling controls can be activated. The monitor is provided with a selector that can be set for operation in one of the two modes as described below. 1.2 MODEL DIFFERENCES The Model 3126 RF Power Monitor/Alarm is identical to the Model 3127 except the Model 3126 has a forward meter with a 15/30/60 kilowatt scale (P/N 2150-090). The reflected meter has a 1.5/3.0/6.0 kilowatt scale (P/N 2150-091).