| 摘要 |
<p>A high definition television broadcast transmission system includes a feature of maintaining a constant transmission output power. A system includes components, such as a digital encoder (12), for providing an information signal. A pilot source (30) provides a pilot signal. A combiner (26) combines the information and pilot signals. A power amplifier (50) amplifies the combined information and pilot signals to a broadcast transmission power level. An automatic gain control (38), located upstream of the amplifier (50), increases gain of the information signal in response to a control signal. The broadcast transmission power level of the information signal is dependent upon the gain applied by the gain control. A sample signal contains the combined information and pilot signals, is derived from an output of the power amplifier (50). A pilot-indicative signal is isolated from the sample signal. The control signal for the gain control (38) is determined using the pilot-indicative signal.</p> |
