IC TDA 8361
The IF
amplifier contains 3 AC-coupled control stages with a total gain control range of greater than 60 dB. The sensitivity of the circuit is comparable with that of modern IF ICs.
The reference carrier for the video demodulator is obtained by means of passive regeneration of the picture carrier. The external reference tuned circuit is the only remaining adjustment of the IC.
The AFC
circuit is driven with the same reference signal as the video demodulator. To ensure that the video content does not disturb the AFC operation a sample-and-hold circuit is incorporated; the capacitor for this function is internal. The AFC output voltage is 6 V.
Circuit TDA 8361
The time constant of the AGC system during positive modulation (TDA8362) is slow, this is to avoid any visible picture variations. This, however, causes the system to react very slowly to sudden changes in the input signal amplitude.