U-segment RF modulator

The U-band radio frequency modulator is a modulator whose output radio frequency carrier frequency range is in the UHF band.
    As can be seen from the figure, its main body is the integrated circuit ICl (LA7051), and the task of IC1 is audio audio frequency and video clamping. The video image signal
is input from the ② pin of ICI, white peak limiting and video clamping are performed in IC1, and then output from the ① pin. The audio signal is input from the ④ pin through the pre-emphasis circuit and
is amplified and FM modulated in the ICI. There are two resonant circuits of the audio carrier frequency oscillator that resonate at 6MHz and 6.5 MHz respectively
to adapt to the needs of different regions of PAL-I/D. The selection of the resonant circuit is controlled by the @ pin voltage. The FM audio signal is output from the @ pin of ICI.
After filtering out the interference signal through the LC series resonant circuit, it is added to the video signal and then sent to the radio frequency modulation circuit. The radio frequency modulation circuit is composed of D2,
D3 and 13. The radio frequency carrier The oscillator is a capacitive three-point oscillator with transistor VT1 as the main body . The modulated signal is also sent to
the lower end of mixer T5. Together with the signal from the antenna amplifier, it is sent to the RF output.