Service manual

STP 11-25R13-SM-TG
S - 6
c. Vertical Synchronizing Pulse
(Vertical Sync). Vertical sync pulses (Figure S-4) are rectangular
pulses that synchronize the vertical scanning motion in the receiver precisely with the vertical scanning
motion of the camera at the program originating point. These pulses are part of the transmitted
composite video signal and have a frequency of 60 Hz. The vertical sync pulses have a duration of 3H
versus 0.08H for horizontal sync pulses (1H is equal to 1 horizontal line or 63.5 usec) which makes
possible the separation of vertical and horizontal sync pulses by relatively simple frequency separation
circuits.
d. Corresponding Blanking Pulse
. Each vertical sync pulse rides on a corresponding blanking
pulse. As shown in Figure S-4, each vertical pulse has six slots, making it appear to be a series of six
wide pulses at twice the horizontal frequency. The slots provide nothing of value as vertical
synchronizing information, but do provide uninterrupted information to the horizontal scanning circuits.
(1) The width of the slots in the vertical sync pulses is approximately equal to the width of the
horizontal sync pulses (0.07H versus 0.08H). The slots are made as wide as possible so that noise
pulses or other discrepancies occurring just before the leading edge of a slot do not disturb
synchronization.
(2) To eliminate problems of nonuniform spacing of the scanning lines as the system scans
successive fields horizontally, and to maintain continuous horizontal synchronizing information throughout
the vertical synchronization and blanking interval, it adds another series of pulses called equalizing
pulses to the composite video signal.
e. Equalizing Pulses
. Equalizing pulses (Figure S-4) occur in groups of six before and after each
vertical sync pulse. Each group has a duration of 3H. These pulses are part of the transmitted
composite video signal.
(1) The equalizing pulses serve two purposes in getting good vertical picture resolution at the
receiver.
(a) They equalize the time periods that occur between vertical sync signals of alternate fields.
(b) They maintain uninterrupted horizontal synchronization throughout the vertical blanking pulse
period.
(2) The pulses are spaced at periods of one-half H so that every other pulse serves as a horizontal
sync pulse.