TM 11-6625-3025-14/ET426-AA-MMA-010/E154 VII210/T.O. 33A1-8-902-1-1
CHAPTER 4
FUNCTIONING OF EQUIPMENT
Section I. OVERALL FUNCTIONAL DESCRIPTION
4-1.
Introduction. This chapter provides a functional description of the test pattern generator. The functional
description is presented in two levels. Section I contains a brief overall functional description of the circuit cards shown in
the test pattern generator functional block diagram, figure FO-2, and section II contains a more detailed description of the
individual circuit card function based on fold-out schematic diagrams in each functional area.
4-2.
Sync Generation. (See figure FO-2). The synchronizing ("sync") generator produces pulses which are used to
synchronize camera, display monitor and other television devices in developing the tv raster. These pulses control the
order in which the television picture will be produced. Four basic types of electrical pulse signals have become commonly
used for such purposes, including H drive, V drive, blanking and sync (see figure 4-1), as described by Electronic
Industries Association (EIA) Standard RS-343. All pulses are generated from a very stable master oscillator which is
crystal controlled. Digital techniques are used to generate pulses at the horizontal and vertical rates of the scan rate to be
used. These include:
a. H DRIVE is a pulse train in which a pulse starts at the end of every television scanning line. Its function is to
mark the time interval between the end of one line and the start of another; the pulses may be used to control horizontal
deflection "flyback" and signal processing. The pulse train is continuous, uninterrupted even during the vertical
synchronizing interval. These pulses are useful for synchronizing an oscilloscope when inspecting the television waveform
at the horizontal line rate.
b. V DRIVE is a pulse train in which a pulse starts at the end of each television field. Its function is to mark the
time interval between the end of one television field and the next; these pulses may be used to control vertical deflection
"flyback" and signal processing. These pulses are useful for synchronizing an oscilloscope when inspecting the television
waveform at vertical field rate.
c. BLANKING is a mixture of horizontal and vertical information intended to control the "blackout" of the
television system during deflection return between horizontal lines and vertical fields. These pulses are wider than drives
or sync to insure that all transitions are made invisible.
d. SYNC is a complex combination of horizontal and vertical pulse information intended to control the decoding
of a television signal by a display device, recorder or other type of video processing equipment. Usually it is mixed with the
video information to produce a composite picture signal (figure 4-2) which is distributed for general
use.
4-1
