Design Article
HD multi-room video distribution over IP-based home and commercial networks
Michael Braithwaite, CTO, NetStreams
4/20/2007 3:40 AM EDT
What is distributed video?
Distributed video is a system where all kinds of video (and audio) signals from A/V source components are routed to remote display locations. At the remote locations display devices such as CRT televisions, flat panel displays, projectors, and projection systems are used for viewing the A/V sources at the head end.
A need for distributed video arises when designing a system that utilizes many A/V sources, and/or many display locations and/or the display locations are distant from the A/V sources. Another reason would be for sharing source components such as a DVD changers, digital cable or satellite tuners.
Traditionally video in a commercial or residential installation has been distributed using two methods -- Broadband (also known as "Radio Frequency" or "RF"), and Base band analog. Both methods have been in use for the past 50 years, and both have inherent disadvantages.
Broadband ("RF")
This is a system design in which each of the A/V source components are connected to a radio frequency (RF) modulator. The RF Modulator takes the internal RGB, YUV, or composite video and audio signals from the A/V source components and generates a PAL or NTSC broadcast signal that can be fed into the distributed video system. The outputs from the RF modulators are then routed into RF combiners and then into large RF amplifiers.
When designing an RF system the RF amplifier(s) need the ability to boost the PAL/NTSC signal level high enough to make it to the farthest remote display location. In a system design where remote display locations are very distant from the head end, the RF amplifier has to boost the signal very high. The goal would be to have RF amplifier gain to achieve a 0dB signal level at the most distant remote display location. Other remote display locations in this type of system would need to be attenuated so that the RF signal would not be higher than 0dB. This involves small passive "tap points" or "tap offs in line attenuators installed at each remote display location.
Figure 1: RF Distribution, typical installation
The wiring topology for a system such as this consists of coaxial type cable, with the most common types being RG6 and RG59. In most designs the coaxial cables are in a home run from the head end to each remote display locations; however there are some deployments with more of a "ring" or daisy chain approach.
Next: Disadvantages of video distribution over RF
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