Deviser S7200 User Manual page 105

8-3.2 Video Parameters Gated Measurement
VITS (Vertical Interval Test Signal)
In the past, engineers often used full-field test signal to test TV systems. This particular test process requires
the field or HE engineer to interrupt the specific channels from broadcasting. In today's HFC networks, for
competitive and other reasons, this is no longer a feasible plan. With the continuous growth of the CATV
industry, it is critical that broadcast TV programs are not interrupted during testing and monitoring of CATV
system performance. VITS, a method of inserting undetectable test signals during the vertical blanking
interval, allows CATV operators to conduct performance testing without disrupting service to customers.
1. VITS insert position provision.
The composite test signal is inserted into an empty, unimportant or undesired line of the vertical blanking
interval behind the sync pulse field, e.g. lines 16-22 or line 329-335 in a 625-line system. (These particular lines
do not typically show, and/or cannot be visualized on the viewable portion of your television screen.)
In 1969, CCIR changed its recommendation for usage of international TV programs from 625 line systems to
VITS. The recommended VITS insertion position is as follows:
The following figures illustrate some of the most widely used VITS signals.
CCIR17 test signal
The first peak from the left is a white flag with peak amplitude of 700mV (relative to blanking level) and a
width of 10µs; a zero carrier reference (base white) for measuring video signal amplitude and depth of
modulation. The second from the left is 2T pulse with a half-amplitude width of 200ns, it is used to measure K
factor. Cable TV systems use K-2T factor to replace echo measurement.
The third from the left is a composite sine square pulse with a half-amplitude width of 20T (2μs). The 4.43MHz
color subcarrier sine wave is filled in the 20 sine square envelope (standard for luminance signal), 20T
modulated chrominance pulse is used to measure Chrominance-Luminance Delay Inequality and Gain
Inequality. The fourth from the left is 5-step luminance staircase signal; every staircase step is 140mV, which
is used to measure luminance nonlinear characteristic.
Insertion Line
16 (329) Data and communication signal
17, 18 (330, 33) International VITS signal position, for
21 (334)
CCIR Line 17
Part III: Background and Concepts
Application
Teletext broadcast
105