Articles and whitepapers
Multiroom Video Over CAT5 (3/4/2006)
Chris Skelton, Bluedelta Design
The age of a single television in the lounge,
with the whole family huddling around it after dinner, has long
passed. The diversity of programming now available makes it extremely
unlikely that any modern family will be able to agree on what to
watch. Long gone too are the days when the bedroom had just a 14"
portable. That's now the 28" widescreen that occupied pride of place
in the lounge - until the new 42" plasma became a 'must buy', and
forced it into early retirement.
While we have entered the age of plasma and
LCD TVs, of bigger and better pictures, and of looming high definition,
it is strange that many multiroom video systems are still being
installed using UHF over coax. How often have you seen a nice flatscreen
with a grainy picture - just because the last few meters of the
link are an ancient bit of coax with a traditional 'TV aerial plug'
at either end?
It is the 21st Century, so what about a wireless
video sender to improve the picture? To anyone who has not seen
one of these in operation, they can look very attractive. But they
are prone to the 'occasional' drop out of signal, or blizzard across
the screen when the microwave is turned on. If you are going to
invest in decent audio visual equipment, you need to ensure you
make the best use of the pictures everywhere.
Why use CAT5?
There are a couple of ways of achieving high-quality
output from your DVD to another device - the most obvious being
SCART cables, although 15 meters of SCART is not only costly, it
is also hard to hide. The industry has been 'playing' with CAT5
for some time, primarily in the field of security video or remote
computer monitors, but it is only recently that systems have begun
to emerge that are either economically viable or truly tailored
to the domestic environment.
Third-generation video-over-CAT5 systems
address these issues by making use of the properties of the twisted
pair wires, namely providing a high degree of noise immunity both
to external sources of interference and to crosstalk between the
separate signals within the cable itself. Provided the relevant
signals are injected at the master sender, and received at a slave
receiver in a true differential manner, then external noise is cancelled.
The main problems up to now have been prohibitive
cost coupled with limited ability and limited fan-out. Today's third
generation video-over-CAT5 devices however, are addressing these
issues and retailing at well under half the price of the previous
The three generations of video-over-CAT5
can be described as follows:
Generation 1 (G1) - passive BALUNs. This
is really a legacy from the CCTV industry, and while useful in some
applications, it is only applicable to single point-to-point links,
i.e. fan-out = 1. It also suffers from very limited range and bandwidth.
Generation 2 (G2) - early active systems.
Some of these are very good, but very expensive too. They often
pass video very well, but some have no provision for audio, most
have no provision for remote control return, and surprisingly, none
at all have the ability to pass on/off/widescreen information to
the remote displays. In addition, G2 systems share a limited maximum
fan-out of 12 or less.
Generation 3 (G3) - current state of the
art. This is truly user-focused, and can supply a seamless audiovisual
experience to each outlet. A G3 system will convey CVBS or S-video
along with stereo audio and full widescreen signalling, so each
outlet essentially behaves like a direct SCART connection. A G3
system should be modular, and able to operate with a fan-out of
16 or more.
G3 systems are designed so that the entry
level cost of a simple point-to-point system is low, but the system
can be expanded when required. So, if the user wants to have their
AV source equipment in a separate communications room away from
the viewing device for example, they can expand the system to have
a second or third viewing location, as well as the ability to watch
from one of several AV sources while still being able to control
from a remote location. All should be easy additions after the initial
system is set up.
Video-over-CAT5 systems can be broken down
to the following key components:
To start with, you will need to interface your video equipment to
the CAT5 network, and pass back any remote control information from
the remote locations back to the source equipment. In its simplest
form, the Master will be a single SCART interface.
In the simplest star-wired systems, this is a compact unit similar
to, but not the same as, an Ethernet hub. It performs the dual function
of video/audio distribution from a Master device to multiple Slave
devices, and of returning remote control information from the Slave
devices to the Master.
The Bluedelta Milestone distribution hub
This is required for more complex systems where multiple sources
need to connect independently to multiple displays. Ideally, this
will incorporate the input interfaces, and provide independent outputs
to the remote TVs. This all sounds very nice, but there can be significant
operational difficulties associated with the user interfacing of
routers, which none of the current systems have addressed convincingly.
Finally, you will need something to connect to the remote TV. In
its simplest form, the Slave device is a compact unit which can
either plug directly into the television's SCART input or connect
to it via RCA. Of course the Slave should have an infra-red pickup
in order to relay remote control commands back down the cable to
The Bluedelta Milestone Slave unit plugged into back of a remote
Infra-red pickup on front of flatscreen, connected to Slave unit
at the back
What about high definition?
All the components required to implement
HDMI in multiple locations will need to be very different to those
used for current systems. Unfortunately there is no crossover between
the technologies, and there is no solution in existence or in prospect
that will deal with both systems together. The best solution is
to allocate a second set of CAT5 cabling to be used separately for
the HDMI link. With CAT5 cable being low cost, it may be worth running
two cables to a suitable face plate at the time of your initial
install, as future-proofing.
Wallplate with two CAT5 sockets
While HDMI is coming, and several companies
are working on CAT5-based point-to-point links, the very high bandwidths
required for HDTV will seriously limit the transmission range available.
In addition, the complexity of the HDCP content protection system
will likely make true multi-outlet networks impractically expensive
for the foreseeable future.
No matter how good your equipment is, it
will be let down by inadequate infrastructure. Remember that you
may need to use many video sources, not all of which will be equipped
with the same interface, so ensure you work with a modular system
that offers interface adaptation.
A multiservice wallplate
The upcoming fourth-generation (G4) systems
will be based on third-generation technology, and should become
available in early to mid 2007. They will support full RGBS and/or
YPbPr and where routers are used, the control issues will have been
addressed. G4 systems will be truly user-focused, supplying a seamless
audiovisual experience to each individual outlet.
A properly-installed video-over-CAT5 system
will be reliable, use suitable interconnect fascias and provide
the best possible service to all outlets. The inherent noise immunity
of CAT5 cabling will stand it in good stead with the growth in wireless
home gadgets. It will be simple to install, especially in houses
already flood-wired with CAT5, and will lend itself to simple upgrade
and expansion, whether to keep pace with new technology or to simply
add a couple more outlets.
Chris Skelton is the Managing Director of Bluedelta
Design, designer and manufacturer of the Smart Scart automatic SCART
switch, Phantom PVR, and Milestone video-over-cat5 cable systems.