Alcorn Mcbride V+ series, User Manual

Page: 234 / 276

14-14 SMPTE Machine Hardware Reference
Video Synchronization
The SMPTE Machine is designed to extract the vertical frame clock from an
external video sync signal. This feature is only used when generating SMPTE
and locking the generated signal to Video sync. This signal should be NTSC or
PAL composite video at the standard sync level of 4.1 volts peak-to-peak.
The sync signal is connected to the SMPTE Machine via a rear panel BNC
connector. If additional devices are to be wired to the same sync signal, a BNC
“T” may be used to daisy-chain the signal. If the SMPTE Machine is the last
device in the chain, the internal 75-Ohm terminator should be connected
(factory
default) ; otherwise it should be disconnected.
A common sync connection scheme is to use the “Gen” output of player to
drive the “C-Sync” inputs of another player, with the second “C-Sync”
connector of that player connecting to a third, and so on. The final player’s
second “C-Sync” connector would go to the SMPTE Machine, which needs to
have its terminator enabled.
The SMPTE Machine may also work with “Black Burst Sync”, if its level is
high enough. Black burst sync is generally provided not at sync level, but at
video level (approximately 0.7 volts peak-to-peak). Signals at this level should
not be terminated with the 75-Ohm terminator. If you are trying to use a video
level signal, have the terminator disconnected, and still can’t get the sync to
work reliably, it is possible to increase the SMPTE Machine input sensitivity by
removing R23. Since this procedure is performed with wire cutters, it should
not be undertaken lightly. It also voids the warranty. But if it’s 3 AM in Abu
Dhabi and your show opens at dawn, what the heck.
Sync Termination
Composite sync signals contain high frequency components. When the signal
reaches the end of the line it has a tendency to reflect back toward the sync
generator. This reflected signal is undesirable because it degrades the “real”
signal. To prevent signal reflection, a terminating resistor is usually placed at
the end of the line.
The SMPTE Machine provides an internal 75-Ohm terminating resistor. The
unit is shipped from the factory with termination enabled (jumper installed).

Configuring sync termination
1. If the SMPTE Machine is the last unit in the daisy-chain, verify that W6 is
present.
2. If the SMPTE Machine is NOT the last unit on the daisy-chain, remove W6.