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自从1965年美国发射了第一颗实用通信卫星(EARYBIRD)以来,卫星通信已从小功率转发器(5～20W)提供专用电视分配业务转向高功率(50～250W)转发,以提供个体和集体收看卫星直播电视业务。为了使地面用户使用性能价格比最好的设备,广播卫星采用点波束技术以获得最大的EIRP,同时选用FM体制传输信号,从而取得了约20dB的调频改善因子。这两点为卫星直播电视体制奠定了基础。
Since the United States launched EARYBIRD in 1965, satellite communications have shifted from dedicated TV distribution services (5 to 20W) to high-power (50 to 250W) forwarding for individual and collective viewing Satellite Live TV business. In order to make the terrestrial users to use the most cost-effective equipment, the broadcasting satellite adopts the spot beam technology to obtain the maximum EIRP, and selects the FM system to transmit the signal, thereby obtaining the frequency modulation improvement factor of about 20dB. These two points laid the foundation for the satellite live television system.