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Installing Freeview aerials Want to see more?
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Installing Freeview aerials Installing a TV aerial for Freeview isn’t too hard if you avoid tall ladders. Just follow our simple tips While most Freeview viewers will baulk at the thought of installing their own aerial to upgrade for digital TV – not least because the external aerial that is preferable requires working on the roof, or high on a wall – it is possible to do the job yourself. Will I need to upgrade my aerial for
01 Freeview?
There’s every chance that if your current TV aerial works well for analogue TV (getting reliable teletext on all five channels is a simple indicator of good reception), you may not need to upgrade for digital TV. However, current digital TV transmissions use different frequencies (and signal strengths) from the analogue transmissions, and after the digital switchover in your area these frequencies may change – in some cases to the same frequencies currently used by analogue signals. So you may need another aerial for digital TV, either now or after switchover. And you may not. If you are converting to digital TV well ahead of switchover, then you may as well try the new Freeview receiver with the aerial you have. If it works, all well and good. If not, then you need to think about buying a new aerial.
Aerial set for vertical polarisation
Aerial set for horizontal polarisation
How to mount the aerial
02 You can use an existing mast or bracket for a new aerial, but it’s not always a good idea. The mast and its fittings may be very old and liable to fail when disturbed by the removal of the old aerial (always take down a redundant aerial) and fitting the new one, or by the increased weight of a high-gain aerial. You may also need to move the mast – to give a clear line of sight to a different transmitter, or to have the DTT aerial as high as possible (so that potential interference from, say, passing traffic, street lights, and thermostats and electric motors inside neighbouring homes are as far below the aerial’s reception line). Make sure that the aerial mast mounts are securely fixed to a robust wall with the correct fixings or lashed to a chimney 2 What Satellite & Digital TV
V-H polarisation: The aerial must be installed with the correct orientation to match the polarisation of the signal it is to receive
with the correct kit (don’t drill into a chimney). Most importantly, before attempting any work at height, think carefully about whether you have the equipment and abilities to survive the experience. How to find the transmitter
03 If many of your neighbouring homes have aerials recently installed for digital TV reception, you can orientate your aerial in the same direction as these – but beware of copying antennas for analogue reception that do not relate to your installation. If neighbouring aerials give a mixed message or you simply want a different transmitter, you need to know where the
transmitter is. Ofcom publishes full details of analogue and digital transmitters used for BBC, ITV and Channel 5 (www.ofcom. org.uk/static/reception_advice/index.asp. html). Using this and a map, you can work out the direction to the transmitter site. Alternatively, the Wolfbane website (www.wolfbane.com/cgi-bin/tvd.exe) does the work for you – just enter your postcode and whether you want to see just local transmitters, distant ones, or those for real DX reception and the website will show all the available transmitters, the details of what is transmitted, and their bearings from your postcode. Wolfbane even gives the estimated signal strength and recommended aerial type – far more
abc guide to...
Available transmitters, in order of signal strength at the reception site
Draws a profile of the terrain between your aerial and the transmitter. Currently only an experimental function
Height of aerial above sea level. With the height of the transmitter and distance to the transmitter, can be used to determine if the transmitter is in line of sight and if any elevation angle needs to be applied to the aerial Bearing from due North to transmitter (requires correction for magnetic variation for accurate compass alignment)
The six multiplexes carrying the Freeview channels
Height above sea of the transmitter
Aerial frequency ‘group’ required
Power of the transmitter
Polarity of the signal
UHF channel number of the multiplex
realistic than any of the simple postcode coverage checkers. How to choose the right cable 04 The best signal from the highest gain aerial can be wasted with the wrong cable between the aerial and the receiver. Poor quality co-ax – once routinely used for aerial installations – won’t work well for digital TV, and good cable degrades with age. So even if you use an existing aerial it can pay to replace the cable. The co-ax cable has two jobs to do – to lose as little as possible of the signal passed from the aerial to the receiver and to keep out unwanted interference along the way. Although you can buy quite reasonable UHF co-ax for connecting a TV aerial, cable made for a satellite dish is
much better, and this should be used in preference. Get the best quality doublescreened satellite co-ax (that is, with both a braid and a foil shield beneath the outer sheath) that you can find, and it will perform well for many years. How to connect up the aerial
05 Unless you have a DTT signal
strength meter you will need to connect the aerial to the receiver to align it, so you should install the cable once the aerial mast is in place. Leave plenty of slack at the aerial and pick a route for the cable that takes advantage of any architectural features to hide it. Make sure the cable is clipped to the wall of the house every couple of feet along so it cannot move in the wind and become damaged.
Glossary Aerial
A device to receive broadcast electromagnetic TV signals and convert them to electrical signals for processing by a receiver.
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.
Polarisation
The orientation of the oscillating waves that make up the signal. Satellite and terrestrial TV signals are usually polarised vertically and horizontally. An antenna intended for reception of one polarisation will reject signals of the opposite polarisation.
Wolfbane explained: An example output from the Wolfbane reception predictor with explanations of the various data
Suggested aerial type required Predicted signal strength (ideally over 50 dBµV/m, but over 25dBµV/m should be receivable with high-gain antenna)
How to align the aerial
06 With the aerial mast securely mounted in the intended position, the aerial is positioned on the mast and the cable connected. Most aerials clamp to the mast and can be fixed in two positions to provide reception of horizontal or vertical polarised signals. Check the transmitter polarisation from the Ofcom or Wolfbane websites. The ‘elements’ of the aerial (cross pieces on the long main strut) show the polarisation, so if the aerial is mounted with the elements horizontal it will receive horizontally polarised signals. Use a compass to find the correct bearing to the transmitter. You can safely do this on the ground – standing beneath the aerial’s fixing position, find a nearby landmark in the right direction. Swivel the aerial around on the mast until it points to the landmark and tighten the clamp to hold it in position. Now you should fine-tune the alignment using either a DTT signal meter or the onscreen signal strength indicator from the Freeview box or TV. You will need someone to relay the readings on the screen. Move the aerial left and right to find the strongest signal. Finally, tilt the aerial upwards a couple of degrees to minimise interference, tidy up the cable slack (reduce its length if necessary) and waterproof the connection. Now you can enjoy all that digital terrestrial TV can provide n Geoff Bains What Satellite & Digital TV 3