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Freeview
Aerials for Freeview Choosing the right aerial for Freeview reception could save you a lot of trouble during Digital Switchover – and save you from the cowboys too Satellite TV offers a choice of thousands of channels, but it is more complex and more expensive to receive than terrestrial TV. If you only want to receive the ‘basic’ four or five channels, or just a minimum of additional free channels, then there may be little point stretching to digital TV by satellite and Freeview digital terrestrial TV is the simpler course. To get Freeview you may need only a Freeview receiver box or a TV with an integrated Freeview receiver. You won’t need a dish for Freeview, however, you may need to upgrade your TV aerial.
estimates say hundreds of thousands of homes will not receive all the Freeview channels even after Digital Switchover is completed across the whole country. Do I need a digital aerial?
03 There is really no such thing as a ‘digital’ TV aerial. Analogue and digital signals require the same sort of antenna. Although you do need an aerial suitable for the kind of transmissions that DTT uses, that depends on the broadcast frequencies and the distance to the transmitter and not whether the signal is digital or not. An old aerial for analogue TV may work well for Freeview reception.
How is Freeview broadcast?
01 Freeview is sent in much the same
Which aerial is best?
04 There is no overall ‘best’ aerial. The
only a few tens of miles. There are not enough transmitter masts to cover the entire country. In addition, although DTT signals pass around and through some objects better than satellite signals, it’s more likely that an obstruction, such as a hill or building, will block the signal from a terrestrial transmitter than from a satellite in orbit above your home. So, whereas there are very few homes unable to receiver satellite TV, those unable to receive a satisfactory terrestrial signal are relatively numerous. Some
Can everyone get Freeview?
02 Unfortunately, no. Unlike satellite
Yagi aerials receive a fixed frequency range 2 What Satellite & Digital TV
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TV, which is broadcast over the entire country (and much of Europe, in fact), DTT broadcasts are from transmitters mounted on tall masts that can reach for
If transmitters in adjacent areas use the same frequency for a multiplex (top) then a home receiving both transmissions would experience interference, so different frequencies are used (bottom) so that a receiver can differentiate between the transmissions.
choice depends on what you are trying to receive and where it is coming from. The Freeview multiplexes are scattered across the terrestrial TV frequency spectrum at different frequencies in different areas. A conventional ‘Yagi’ TV aerial (with a reflector plate or grid at the back and a line of ‘elements’ in front) works best over a limited frequency range and is often designed for a particular ‘group’ of frequencies. ‘Wideband’ versions do not operate equally well across all frequencies. However, Yagi aerials can be designed for high gain, or even super high-gain, for weak DTT signals in fringe areas. Better wideband reception – to receive all possible frequencies – can be had from a ‘log periodic’ aerial (with no rear reflector and decreasing element size along the antenna). Although these are usually lower gain and so best suited only to moderate or high signal levels, they are
Super high gain aerials may be too powerful after the switch
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way as the original analogue TV signals have been transmitted for over 50 years, and received with a normal TV aerial. The 100 or so digital channels are transmitted in six ‘multiplexes’. The frequencies used differ in different areas so that a home in range of two or more transmitters (as many are) does not suffer from identical transmissions received out of step, causing interference between them. In the next couple of years the process of Digital Switchover – already begun in some regions – will turn off the analogue transmissions around the country, leaving DTT as the sole means of receiving TV signals through an aerial.
A high gain variation on the Yagi design
An external aerial is best for reliable Freeview reception but you may be able to get away with an internal aerial in areas close to the transmitter. A loft aerial is the second choice, provided this is a ‘full-sized’, proper aerial. Remember that the roofing material will reduce the signal strength. The aerial should not be sited near large metal objects (such as a water tank) that can cause reflections and it won’t work at all if your loft space is insulated with metallised or foil-covered batts. A set-top type aerial is suitable in very few cases. Even if an existing set-top aerial works after a fashion for analogue reception it is unlikely to do so for Freeview (although there is no harm in trying out a set-top aerial you already have). Don’t be fooled by claims of miracles from a built-in booster amplifier – it won’t help. How it may all change anyway
06 When Freeview began (in 2002) the extra transmissions were fitted ‘between’ the analogue frequencies used, and at a lower power so they would not interfere with existing television. When an area undergoes ‘Digital Switchover’ (as some areas already have) the strong transmitters carrying the analogue signals are turned off and the digital transmissions will either change frequency, increase in power, or both – or remain as they are. It all depends on your local transmitter and those in adjacent areas. This means that a narrow-band aerial that works well pre-switchover may not pick up all the channels after switchover – even though the transmissions are
Range of frequencies suitable for ‘grouped’ aerial
Changes from (imaginary) pre-switchover transmission frequencies (top) to a post-switchover situation (middle) would require a difficult compromise between wideband and high-gain reception, while another postswitchover scenario (bottom) would render unnecessary an expensive high-gain antenna bought before the switchover.
Transmission power still requires high gain aerial
Frequency Range of frequencies too large for ‘grouped’ aerial
Transmission power no longer requires high gain aerial
Frequency Range of frequencies suitable for any aerial
Philex/Labgear
Set-top aerials often don’t work with DTT
Transmission power requires high gain aerial
Frequency
Transmission power
Can I use a set-top aerial or one in
05 the loft?
Transmission power
also particularly immune to local interference. The Wolfbane website (http://www. wolfbane.com/cgi-bin/tvd.exe) will tell you where your nearest transmitter is, the frequencies it uses, the signal level you can expect and even suggestions for aerial types.
Transmission power
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stronger – because they have moved out of its group. On the other hand, a wideband aerial may pick up interference from transmissions from adjacent areas that are stronger after switchover and require filtering to be added. In addition, a new high-gain aerial required to get all the channels before switchover may be unnecessary afterwards because the digital multiplexes have moved to the old analogue frequencies at a higher power. To complicate matters further, as HD digital terrestrial TV is introduced – first as test transmissions in a few areas and later across the whole country – this will cause further changes to the transmission of standard-definition channels. All of which means that if you have little experience of TV aerials it is wise to consult with a local professional with knowledge of the signals in your area and exactly what works there. Contact the CAI at www.cai.org.uk to find someone in your area n Geoff Bains
Glossary DTT
Digital terrestrial television. Digital television signal broadcast from ground-based transmitters to DVB-T standards.
Freeview
The network of TV and radio channels and interactive services broadcast free-to-air in the UK on (DTT). Owned by the BBC, BSkyB, Channel 4, ITV and Arqiva.
Multiplex
Transmission at a single frequency containing a number of digitally encoded and compressed TV and/or radio channels. Freeview operates in six multiplexes (1 and 2 for the BBC and A-D for commercial broadcasters), each carrying up to about 12 full-time TV channels. One multiplex will be used for HD transmissions in the future.
What Satellite & Digital TV 3