b. By using suitable keying equipment, it is possible to introduce information
onto one or more of these blank lines to be transmitted to a specific destination.
If desired, this information can be blanked out at the receiving point before the
signal is put on air, or since it is not normally visible on the receiver, it may
be broadcast.
c. The NTSC established VITS on lines 17 and 18, and line 19 for transmission of
the VIR test signals.
The Major networks and Bell Systems, working through the
Network Transmission Committee, are working to development methods to place other
test and coded signals into the other lines of the vertical blanking interval.
d. The advantage, of course, of introducing these signals in the vertical
interval is that a system can be checked in service, and digital information can be
passed along the transmission links while a program is actually being transmitted.
To this end, it is also desirable that all these signals be available for nearly
simultaneous observation, and this is the ultimate objective.
2. The specification and standards for the VITS are illustrated in Figures 3-6, 3-
7 and 3-8.
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