These days, most homes with satellite TV or digital terrestrial TV also have more than one TV set. However, secondary TVs require either a separate receiver for each screen (which is rather expensive, especially if it's a Sky Digital pay-TV that you're watching) or a means to distribute the signals from the receiver to more than one TV screen.
UHF distribution is the most commonly used technique but there is one big problem with any UHF distribution system - it uses UHF! Although a modulated UHF signal is relatively easy to send around the home and cheap to service at each end of the cable, it provides the worst possible quality of video onscreen. What's more, the audio carried is also low quality and in mono only.
We have looked at a number of techniques and products to distribute signals in other formats and these methods are slowly gaining popularity among digital TV enthusiasts.
One of the easiest systems to implement is based on CAT5 computer network cable and Keene was quick off the mark with a system (the CAT5 Blaster) to use that a couple of years ago. Now a simpler and cheaper system has been introduced - the C5KDA distribution amplifier.
The CK5DA is a modular system with a single distribution amplifier unit and up to four receivers for secondary TV screens. Although it is relatively expensive (certainly far more than any UHF-based system), it has the potential to pipe decent quality TV around the home.
Balanced signal
The system works by using each of the four twisted pairs in a CAT5 cable to carry one signal in a 'balanced' format. This means that rather than send the signal as a voltage relative to a common earth connection, the two wires are used to carry voltages opposite to one another.
The two wires are entirely unshielded and simply twisted together so that any interference picked up by one is also picked up by the other and they cancel each other out.
The other great advantage of CAT5 cable over the co-ax is that it's pretty cheap (about £25 for a 100m reel) and easy to lay around the home because it's tough and flexible. You can even buy long ready-made cables if you don't want to wire up your own.
