Specifications

DIGITAL VIDEO RECORDER PROBLEM SOLVING.
The new digital revolution has brought us many new and exciting products for
the CCTV industry. The DIGITAL VIDEO RECORDER or (DVR) may be one of the
most important upgrades that can be made to any CCTV system. The DVR takes a
camera video signal and converts it to a digital bit stream and saves it on a
computer hard drive. It can then be played back with remarkable fidelity. This new
technology brings with it a new set of problems and solutions. This article will
discuss some of the problems and solutions for DVR installations. To understand
the problem we must look at the standards.
STANDARDS.
A video standard was developed by the
Institute of Radio Engineers so that all
manufactured video equipment would be compatible. The unit of measure for this
standard is the I.R.E. Unit. One I.R.E. unit is equal to .007142 Volts peak to peak. A
Black and White (B/W) video signal is 140 I.R.E. units equal to 1 Volt peak to peak.
A color video signal has three vital standard measurements the SYNC = 40 I.R.E.
units, the WHITE = 100 I.R.E. units, and the COLORBURST = 40 I.R.E. units. Both
the B/W and Color signal measure a total of 140 I.R.E. units, but unlike the B/W
signal the Color signal measures 1.142857 Volts peak to peak. The additional
0.142857 Volts peak to peak is caused by the color information called "CHROMA" in
the video picture. It is a common misunderstanding that all video is 1 Volt peak to
peak. Only a B/W video signal is 1 Volt peak to peak, a Color signal is 1.142857
Volts peak to peak. Now how does all this relate to the DVR problem?
THE PROBLEM.
When properly installed the DVR does not output a video picture, displays a
"NO VIDEO" image or has a blank blue video screen. Yet if the video input signal is
connected to a monitor it displays a video picture. At first you might think that the
DVR is defective, that is very unlikely. It is more likely to be a video level standards
problem.
HEADROOM IN THE DVR.
Most DVR's are designed to accept a video signal of 1 Volt peak to peak with
some extra range known as "headroom". This headroom allows the video signal to
exceed the 1 Volt peak to peak by some percentage. Usually 20% over the 1 Volt
peak to peak video level. That makes it possible for the equipment to accept a video
signal of up to 1.2 Volts peak to peak. The standard Color signal measures
1.142857 Volts peak to peak so this amount of headroom should be adequate.
CCTV TRAINING MANUAL PAGE 12 OF 28