The AR6A Single-Sideband Microwave Radio System: The Traveling-Wave-Tube amplifier

This paper describes the amplifier for the AR6A radio transmitter, which consists of a Traveling-Wave Tube (TWT), its magnetic focus system, and driving power supply. The amplification of single-sideband modulated signals requires an unusually low intermodulation noise level and relatively low thermal noise power at the amplifier output. Further, owing to the use of predistortion to achieve the overall repeater intermodulation level objective, the amplifier must perform at high stability. These objectives have been met by choosing suitable TWT design parameters, operating the tube far below its saturated power capability, and devoting close attention to the details of tube construction. The power supply provides well-regulated heater, helix, and collector voltages to control the TWT gain. The supply also regulates the beam current. Current detection circuits protect the tube and power supply from tube internal arcs.