General Instrument C6M-II, Руководство по установке

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C6M-II Installation Manual
Section 4
System Block Diagrams
This section describes the operation of the C6M-II through a series of block diagrams. The text
is keyed to letters on the block diagrams.
Video to IF Modulation System
Figure 4-1
Video to IF modulation system
A If the modulator option board is installed, baseband video input switching is available. The video
switch includes a Video A level sensor which automatically switches to Video B when the Video A
signal level is low or absent. Audio input switching follows the video input selection. A rear panel
connection provides external control.
B Video AGC is provided with the modulator option board for use with varying video signal levels and
when switching between video sources at different levels.
C The video system is applied to a dc clamp circuit. The dc clamp can be disabled through the
menu.
D The clamped signal is applied to a variable gain stage to permit depth of modulation adjustment.
Video modulation is controlled through the video modulation entry on the main menu.
E A dual diode bridge circuit provides amplitude modulation.
F The modulated IF output is buffered and then applied to an all-pass delay equalizer which corrects
the total group delay response error generated by the C6M-II system.
G The signal is bandpass filtered to remove unwanted frequencies at the
PIF OUT
connector on the
rear panel.
H The unmodulated 45.75 MHz carrier is generated by a phase-locked loop which locks a voltage
controlled oscillator to an internal 2 MHz reference.