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ABC guide to... Step-by-step guides to understanding digital TV
ion part 2 t u ib r t is d . 0 01 2 t s u g u A
Loftboxes: one cable for TV and radio
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distribution part 2
The location of your main AV equipment need not dictate your viewing pleasure. Consider using a loftbox to hide away your signal splitting and amplification Using just UHF signals, you can implement a surprisingly comprehensive distribution system for your home with relative ease – if you make use of a loftbox to provide much of the splitting and amplifying electronics. From simply watching your Sky reception in other rooms, to a complex system for Freeview, radio and Sky+ piped around the home, a loftbox takes out much of the hard work – and keeps down the cable requirements to just two cables to the living room and a single cable to each other TV point. What a loftbox can do for you 01 A loftbox is basically a UHF signal distribution amplifier. It sends the TV aerial signal to a number of points around the home (four or eight TV points are most commonly provided). Unlike a standard distribution amplifier, a loftbox also distributes FM and/or DAB radio, and takes in a satellite LNB feed and adds all the signals together to send them down to the AV gear in the living room on just one cable. Crucially, a loftbox also takes a return feed from the UHF output of the satellite receiver and distributes that alongside TV and radio signals to each TV point (where a diplexing, or decombiner, wallplate is fitted to separate the TV and radio signals, with connectors for each). This means that with just two cables (instead of four) between the loftbox and the living room, and one to each other TV point, you get all the terrestrial TV and radio and the tuned satellite channel at each and every TV point. Instead of a satellite receiver, you can use the return feed line to carry the UHF output from any AV equipment, and you can daisychain the devices (e.g. satellite receiver, DVD recorder, Freeview or Top Up TV box) so all the outputs are available around the home. In addition, loftboxes are also compatible with TV-Link type remote relays, so you can use a TV-Link ‘eye’ to control the receiver and other AV
equipment from any of the TV points. Many models also include another UHF input to take the feed from a security camera. What are the downsides of a
02 loftbox?
Although a loftbox will distribute digital terrestrial UHF signals (from your aerial), your satellite receiver and other AV equipment produce only analogue modulated UHF output – with relatively poor quality and mono sound, to boot – so all your secondary TVs must include analogue tuners to be able to watch the output from the satellite receiver or other AV gear. A loftbox system is economic on cable, but you do need to use cable that’s good enough to carry the signals used and because the system carries both satellite IF signals, UHF and radio signals you should use the absolutely best-quality cable you can lay your hands on. Don’t skimp on the quality of the diplexing wall plates either, as cheap units here will allow interference free rein. Remember, too, that you’ll never get a good signal out if your aerial is not up to scratch. The most common cause of problems, however, is probably the crowded UHF spectrum. It can be hard (but it is essential) to find suitably empty spaces for the AV equipment’s output channels that do not interfere with the existing terrestrial transmissions and can be distributed about your home untarnished. Where to put the loftbox
03 It’s not called a loftbox for nothing and the loft is often the ideal place for one. This keeps it close to the aerial – the loftbox includes an aerial signal amplifier and so it is best placed just a short cable length away from the aerial itself – and fairly central to the other TV points. Remember that if your loft is well insulated, it can get very hot up there on warm days so, being mains powered, the loftbox should be installed on a non-
flammable surface with plenty of ventilation. If the cable route from your aerial to the loft is too long you could use a separate masthead amplifier, or you may be better off installing the loftbox elsewhere – say, in a (cool) airing cupboard, the cupboard under the stairs, or another central location. It can be placed wherever is convenient – where it’s out of the way, where the cable run to the aerial is quite short, and where there is mains power available. Which loftbox to choose
04 Global Communications came up with the loftbox idea over 10 years ago and many manufacturers have since copied the idea. In terms of performance and the effect on signal quality, all loftboxes operate in much the same way and there is not a great deal to choose between the different models available However, the robustness and standard of construction of loftboxes can differ, so it’s not just a question of price. You will, of course, need to choose between the models on offer to select the required number of outputs and the required facilities – Sky+ and/or multi-room compatibility – although additional outputs can be added with a
Glossary Co-ax cable
Cable for carrying the signal in a terrestrial or satellite TV system. Coaxial cable contains a central conductor to carry the signal and a surrounding shield, insulated from the central core, to provide the ground connection and prevent radio interference picked up by or radiated from the central conductor.
UHF
TV signal with picture and sound information modulated on an ultra-high frequency radio carrier of 470-890MHz.
abc guide to... simple UHF distribution amplifier and a ‘standard’ loftbox system can be later upgraded for multiple LNB feeds. How a loftbox can cope with Sky+
05 For a dual-tuner system such as that used by a Sky+ or Freesat+ receiver, two LNB feeds from a quad LNB are required. Although you can, of course, use a separate third co-ax cable laid between the dish and the living room AV stack, a special loftbox designed for Sky+ combines the second LNB feed with the
TV aerial
return UHF signal on the second co-ax cable from the loftbox, so just two cables are still required. Alternatively, a diplexer may be added to the system with an ‘ordinary’ loftbox to share the second cable between the second LNB feed and the UHF return, with another diplexer (or a suitable wallplate) in the living room to separate the two again there. How a loftbox can be used with
06 multi-room installations
As well as dual-tuner capability, the Triax
DDU range of loftboxes include inputs for two further LNB feeds for two of the TV points, so in two other rooms you can watch independent satellite channels as well as the DTT, FM, DAB and AV channels available throughout the home. You can add the same feature to other loftboxes by including a combiner on a loftbox TV point output, to combine another LNB signal with the feed to that output, and a three-way triplexing wallplate at the other end of the cable to separate the signals again n Geoff Bains
Dish with quad LNB
FM aerial
Triplexing wallplates
TV4
TV2
TV1
TV3
Diplexers to add two LNB feeds (included in multi-room loftbox)
DAB aerial
Diplexing wallplates
Diplexer to add second LNB feed (included in Sky+ loftbox)
Diplexer to separate LNB feed (included in Sky+ wallplate)
RF out2 Satellite receiver LNB2
RF out1 Main TV
LNB1
Aerial in
Triplexing wallplate with additional return socket Radio tuners
RF out Aerial in DVD recorder
As complex a loftbox system as you’re likely to see, providing terrestrial TV, radio, Sky+ channel, and a DVD recorder output to four other rooms along with independent satellite feeds for receivers in two rooms – with only a standard loftbox at its heart. All the separate diplexing units can be dispensed with if the right loftbox is chosen