User`s manual

Alcorn McBride Digital Video Machine HD User’s Manual Rev 1.0
14
R3 - 75Ω Video Sync Termination
When distributing video sync, it’s standard practice to terminate every dedicated video
sync line with 75Ω. An ideal system design would provide a dedicated sync line for
each DVMHD from the video sync generator. However, there are circumstances
where you may need to split a single sync line (typically done using BNC ‘T’
connectors) so that it can be shared with multiple DVMHD’s. In this situation, having
termination enabled on every DVMHD in the chain could easily over terminate the line,
degrade the signal, and result in the DVMHD’s being unable to lock to the sync input.
When video sync is distributed in this way, you should disable the 75Ω termination in
every DVMHD except for the last one in the chain.
Switch #3 of the right bank of DIP-switch allows you to disable the 75Ω termination if
necessary. By default, the DVMHD ships with this switch in the ON position. If you
need to disable the termination, just set this switch to the OFF position
R4 - Sync Input Type (C-Sync/Blackburst)
There are two common types of video sync sources; Composite Sync (C-Sync) and
Blackburst. A typical C-Sync signal operates at a peak-to-peak voltage of 4V.
However, Blackburst sync signals are typically much lower at less than 1V peak-to-
peak. This DIP switch settings allows the DVMHD to reliably support both types
despite this drastic difference in signal amplitude.
Switch #4 of the right bank of DIP switches is used to select between the two sync
types. By default, the DVMHD ships with this switch in the OFF position, which
configures the sync input for Blackburst. If you want to connect a C-Sync generator to
the DVMHD, you’ll need to set this switch to the ON position for C-Sync operation.
75Ω
Off
75Ω
On
Right
Bank
Blackburst C-Sync
Right
Bank