Choosing a new TV aerial for Freeview

In this area to receive Freeview via your aerial, you need to be receiving your signals from a main Transmitter. The ones you can receive in this area are Mendip, Stockland Hill, Beacon Hill, Isle of Wight, and possibly Hunts Haw Cross. These are the main transmitters that cover our part of the country. You cannot receive them all and some of you may not get them at all.

Horizontal alligned aerialIf your aerial is Horizontal e.g. the elements are in a flat plain, then you are probably on a main Transmitter. However there are a limited number of relays which are also horizontal; these may only cover a very small area such as the one at Ramp sham. At the moment none of the local relays in this area carry digital. If your aerial is mounted vertically i.e. with the elements mainly in a vertical plane, then you are most likely to be on a relay transmitter.

vertically alligned The main requirement for receiving digital television is a good signal. This is not something you can see on your own TV, because a digital TV signal seen on an analogue TV just gives a snowy picture as if the aerial is unplugged.
The Post Code check is only a very approximate guide and means, if you have a reasonably good aerial and cable, there is a good chance you will receive the signals. This does not mean that other areas cannot also receive the signals with a change of aerial.

Traditionally, Aerial Installers in this country have just put up the cheapest aerial they could get, and pointed it at the nearest Transmitter or relay. This worked well, as most people had no idea what a really good picture looked like, and if the picture was a little snowy the reason given was " they are all like this here as it is a poor signal area" with which the installer left. Most installers did not have a signal strength meter and just pointed it in the approximate direction. You, the customer, believed what he said as you had nothing to judge the picture by.

Now many of you have seen the reproduction from DVD, digital satellite etc. and know what a picture should look like. You go out and buy a wide screen TV and suddenly that just passable picture on the old TV looks very poor and grainy - not at all like your neighbour’s SKY pictures. Here you start to see the difference between Analogue and Digital Pictures. So you start to think about Freeview.

Triax 52As already stated, in order to make Freeview work well you need a good strong signal. Assuming you can pick up signals from the main Transmitter, you will need a good quality aerial which has been "Bench Marked" to ensure it meets the appropriate BS-EN standards (we use the Triax Unix 52); most of the major aerial manufacturers have aerials to this standard (see CAI Web Site).

 In addition, double Screened, low loss coaxial Cable to BS EN 50117 standard is required. This can be identified as it has a copper braid with a layer of copper foil inside it, and the cable is normally marked as well. Cable with tin foil, often called RG6, does not meet the standards required. If you live some distance from the transmitter you may also need a mast head amplifier. Again an amplifier in a plastic box is not good enough. You should use one with a complete metal screened case around it.

If you are using an aerial installer, try and use one who is CAI registered - the CAI web site has a list of installers in your area.

Your installer should have a signal strength meter to align your aerial, as digital reception is very critical. He should also be able to measure the Carrier to Noise level of the signal. If you ask him, he should say you have digital signals of at least 45 udB at your TV point, and a carrier to Noise level of better than 28 dB.

One of the great advantages of Freeview is its rejection of Ghosting. You may be using a relay because of strong, but poor quality signals from the main transmitter. Digital does not suffer from Ghosting.

Digital Problems:- If you are in a fringe area, your digital signals may sometimes break up. This is often caused by impulse noise in the same frequency. Sources of impulse noise are many and varied. Car ignition, central heating systems, petrol garden tools, shower pumps, etc., in fact if it is electrical, it may cause interference. This is a problem which should disappear in the future when power levels are increased. The Stockland Hill transmitter is only at one quarter power of the IOW transmitter at the present time, but this should change in the future.

Pricing:- Correctly installed digital aerials are not cheap. A recent survey gave prices from £160.00 + VAT for a full installation with aerial, mast head amplifier etc., so beware of someone offering to do it for £50.00. And make sure you have a proper name, address and headed bill from the company, and check that they are insured for roof work. Comments such as "It’s covered by your house insurance "are not valid answers! Also just a mobile number should arouse your suspicions. Over the next few years there are hundreds of thousands of aerials to be upgraded, and unfortunately, some people see it as an instant money tree.

Mike Toms.  Tower Hill Technical Services

 

You can view the BBC film clip on this subject, which offers further information on TV reception problems

 

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