30 September 1988
video distribution amplifiers are available to provide delay beyond one
compensation that is superior to coax and passive video delay lines. Pulse
DAs are available to allow for adjustment of pulse delay of up to four
microseconds and regenerate the pulse to eliminate distortion.
Video processing amplifiers have a fixed electrical path length even
though regenerated sync and color burst are adjustable.
delay of a video processing amplifier can be about 225 ns.
Sometimes multiple studio facilities have the output of one switcher
feeding a second and both share some common video sources.
instance, the common video sources to the second switcher will need to be
delayed by the path length of the first switcher.
This delay may be as
little as 50 ns for a small routing switcher, 700 ns for a large production
There are products available to aid in system design.
One is the
isophasing system, an automatic delay distribution amplifier, which will
correct source timing errors up to plus or minus 15 ns.
a. The isophasing system can provide up to 32 channels with 5 outputs
each, and keep all outputs within one degree of the subcarrier phase. This
unit simplifies system design and daily system maintenance.
b. Once all the timing requirements of the equipment are known, lay out
a system plan on paper. It is important that a specific piece of equipment
be defined as the zero timing point. It will become the timing reference by
which all calculations and measurements are made. This reference should be
a source in the plant that is not easily altered, such as the test output
The illustration in Figure 2-1 shows a small system that will use
cumulative delay to achieve system timing.
This system consists of a
camera, a character generator, two 1/2-inch and one 3/4-inch video cassette