Promax GV-698, Instruction Manual

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- Oscillators which generate the carrier frequencies needed for the two
standards (B/G and I) of 5.85 MHz and 6.552 MHz are 90º out of phase and
go to the inputs of the modulators. The outputs of the modulators are
summed and will form the signal to be transmitted.
l) RF modulator
The radio-frequency signal is AM modulated by the video signal through a
diode modulator. These diodes are suitably polarized in order to achieve the
best possible modulation over the wide range of frequencies covered by the
generator. The carrier frequency is generated by voltage controlled oscillators
(varicaps). The oscillator selection is carried out, as the control voltage in
tuning, by a PLL thus achieving a synthesized output frequency.
m) Main board
The base board is responsible for the interconnection of all the boards, and in
addition, for the generation of all the necessary voltages (+5 V, -5 V, +12 V,
+33 V). The keyboard and the majority of output connectors are also placed
here.
05/96 GV-698