FROM THE BENCH
E-mail: fromthebench@gcmagazine.co.uk
Home networking in practice Alan Bennett examines the various ways in which TV signals and data can be distributed in the home
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he proliferation of Smart TVs and PC use has increased the number of connections to the phone line in homes, even though many of the latter have wireless connection. At the same time, the amount of TV aerial work has dropped off tremendously since analogue switch off, not only because the necessary upgrading has been completed, but also because the stronger and more robust digital signals have enabled Freeview transmissions to be received on aerials (even broken ones!) which would not have sufficed for analogue reception. Many dealers and aerial contractors, then, are turning their attention to home networking – and even solar energy, but that’s another story...
UHF co-ax In-home UHF distribution amplifiers and co-ax cable networks, originally installed for analogue TV distribution, are now handling Freeview digital signals and in most cases making a good job of it – and, of course, carrying a lot more channels and programmes than before. Even so, they can introduce a problem, arising from the boosting of carrier strengths since switchover. This can overload distribution- and masthead amplifiers, causing data corruption. The effect, of course, is picture freezing, streaking and pixilation. It depends on signal propagation and aerial gain at the channel frequencies involved, and may be intermittent and erratic. The solution is to reduce signal strength at the amplifier input by removing masthead or booster amplifiers or by fitting attenuators as necessary. In some cases the distribution amplifier – where it has only a few outputs – can be removed altogether and replaced by a passive splitter; simpler, more reliable and needing no power supply. In new installations we find it simplest, where circumstances per-
mit, to install the distributor (whatever form it takes) under the eaves and run the cables externally to the rooms where outlets are required; this saves all need to disturb carpets and decorations, cut joists, chase walls etc. It’s also simple to modify and to diagnose any faults which may arise. The same applies to multi-room satellite operation.
Analogue cabling I understand that the majority of links between set-top boxes, disc players etc. are at present still analogue, which continues to give perfectly good results in standard definition so long as RGB (as opposed to composite) links are used. For this a cheap and effective distribution system is available from Keene Electronics. Known as Video-over-Cat5/6, it uses twisted pair cable of the sort intended for computer data links. It can carry high-quality RGB video and stereo sound over distances up to 100m, carries a link-back path for remote control zappers, and connects to Scart sockets.
Streaming video A PC or media player streams video in digital form to any point in the home via Ethernet cabling or Wi-Fi (wireless) links. For those not yet into them, media players acquire (from phone lines and over-air transmissions), control and launch for home distribution digital TV signals without the need for a computer, which the latter would be somewhat wasted on this task. Media players often include HDD video storage as well, also in some cases a catch-up TV system. Some features of media players have now been overtaken by the likes of YouView and Google TV, however, and some customers’ requirements could be taken care of more simply by these. Ethernet cabling is generally used where a physical link is involved in video/data streaming; it uses J45 plugs at both ends and can
be hand terminated or bought in various pre-plugged lengths. Run length can be much greater than with HDMI cables so that HDTV signals can be taken to any point in the house, and there are no compatibility or ‘handshaking’ issues. Powerline distribution systems, once used (with considerable trouble!) for analogue transmission, are available in the form of extenders for Wi-Fi and Ethernet links. They plug into 13A wall sockets at each end and can retail below £100. For distribution of HDTV signals between HDMI connectors AEI offers a DigiSender type HD PRO. Also available are the HD Juice Box and Power Internet type PE Socket for extending Ethernet cable systems. Sometimes Powerline links can be compromised by interference, radiated to (e.g.) radio receivers, and picked up from appliances like electric motors.
MoCA This stands for Multimedia over CoAxial, and can be used, as well as for new installations, on in-home co-ax networks originally put in for the distribution of analogue TV signals. It carries Ethernet data for sound and vision. The plug-and-play MoCA adapter (e.g. Asheridge echoBox) is fitted at each point where Ethernet coupling is required, the first of which is hooked up to the Ethernet router provided by the ISP. There is no need for configuration or auto-seek by the connected devices, and amplifiers/splitters on the network handle the signal with ease. MoCA can be used in a cable already carrying Freeview signals. It is virtually immune to interference, has a very wide band (135Mb/s) and a short latency of 5ms, 4-6 times less than typical Wi-Fi and Powerline systems. For more information on MoCA call Asheridge on 01494 794770 or visit one of these sites: www.ethernetovercoax. co.uk or www.mocalliance.org JAN/FEB 2013 GET CONNECTED
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