AUTOMATIC GAIN CONTROL SYSTEM OF TV RELAY BROADCASTING MACHINE

摘要

PURPOSE:To prevent a voice signal from being amplified more than the prescribed level in an automatic gain control circuit of a TV relay broadcasting machine, by controlling the gain by the arithmetic result of the modulated signal and the voice signal. CONSTITUTION:Both the video component and the voice component are detected through the video wave detecting circuit DET2 and by the signal E(t) partially connected by the output band pass filter BPF. The peak value f2(alpha) is detected by the peak detecting circuit DET1, and at the same time the voice level f3(alpha) is obtained by the voice level detecting circuit DET3. These factors are added together by the adder circuit ADD to obtain f4(alpha). This addition signal f4(alpha) receives an error amplification through the error amplifier DCAMP, and the output is kept at a constant level via the automatic gain control circuit amplifier AGCAMP. As a result, the amplification factor of the voice signal is reduced less than the prescribed level even in case the video carrier component of the input signal does not exist.