Controlled-Carrier Transmission of AM/VSB Television From Space

Television broadcasting from space, using AM/vestigal sideband (VSB) modulation, requires high satellite power. A method of reducing the necessary prime power, while maintaining signal quality, is described. The method, termed controlled-carrier transmission, is a form of automatic level control at the transmitter that permits the power supply (e.g., solar array plus power conditioner) to be designed for the average long-term power demand rather than for the maximum average power demand, for which ground transmitters are conventionally designed. By this means, power reductions on the order of 30 percent, depending on the type of power amplifier used, may be obtained resulting in significant cost and weight savings for AM broadcasting satellites. A laboratory simulation of the proposed method was set up and the resulting pictures were subjectively evaluated. These tests indicate that, for practical purposes, the average viewer found no difference between conventional and controlled-carrier transmission.