| 摘要 |
An improved automatic gain control (AGC) for a television transmission system comprising a transmitter for transmitting a TV signal via a transmission path to a receiver and having a certain bandwidth in which said transmitter includes a generator for generating a baseband TV signal which can be pre-emphasized, and a variable gain amplifier responsive to the baseband TV signal to produce an amplified baseband video signal. The AGC system comprises a band eliminating filter responsive to the baseband output signal to produce a control signal whose amplitude reflects the change in energy content of that portion of the TV output signal lying outside the allowed transmission bandwidth. The variable gain amplifier is responsive to the control signal to vary its gain substantially inversely as the out-of-band energy content varies. At the receiver a detector detects a component of the received TV signal which has known characteristics, usually constant, in the absence of the gain introduced at the transmitter. The detector produces a control signal which controls an amplifier to compensate for such gain and return the TV signal to its original form.
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