30 September 1988
Learning Event 4:
DESCRIBE THE USE OF A SOURCE-SYNCHRONIZING GENERATOR TIMING SYSTEM
Most of the difficulties encountered in system design can be avoided
This system provides maximum
flexibility and the best SC/H phase stability. The approach below will be
used with the same equipment employed in the previous delay system.
a. This time, rather than using the camera as the reference at the
switcher input, the master synchronizing generator's color bar will be used.
Because these color bars are fixed in their time relationship to the other
outputs of the master sync generator, they make a rock-solid, SC/H phase-
correct reference. All the sources still need to be in exact time at the
switcher input. The SC/H phase pulse drives will be provided to the camera
and character generator by their own dedicated source sync generators.
b. The source-synchronizing generator has the convenience of a single
line locking signal, and output advance or delay, relative to the lock
This results in a much simpler system to design and
maintain, and one that uses far less cabling. There is also redundancy in
the system, since the source sync generators will continue to free run if
the master should fail.
c. Camera 1 still requires drives which are advanced 850 ns to produce
a timed, composite video output; however, this advance will now come from
the source-synchronizing generator.
The above is true for the character
generator and video switcher, if they each have a dedicated source-
Final system timing is now a matter of looking at the switcher output
and comparing each of the sources to the master sync generator's color bars.
Each source-sync generator is adjusted to time the source it is driving. If
the source device has a subcarrier phase control built in, you should adjust
the horizontal phase using the source-sync generator and subcarrier with the
source device's SC phase control.
This adjustment will establish correct
SC/H phase; however, the source sync generator may need adjustment. A SC/H
phase meter will allow the source to be SC/H phased prior to adjustment of
the source-synchronizing generator for final timing.
Sync and subcarrier for the video processing amplifier should come
from the switcher source-sync generator. The source-synchronizing generator
on the video switcher could be removed and the video switcher and the
processor could be driven directly from the master sync generator.
would require placing about 430 ns of delay in the color bar path going to
This is the amount of delay required to generate switcher
color black and background from the applied drives.