Transmission/Technical Information

How can I improve my television reception?

The trouble with television signals is that they can get affected by almost anything as they fly through the ether from our transmitter to your aerial. Unfortunately, this means that we (or any other broadcaster for that matter) cannot guarantee that any aerial in any place will be able to receive a satisfactory signal. As a matter of general principle, TV signals travel in straight lines, so anything that gets in the way between the transmitter and your aerial may stop or at the least degrade the signal. Your aerial must be able to 'see' the transmitter. However, things aren't all that bad (usually), and there are many things that a viewer can do to improve their TV reception.

First, the ground rules. The people who decide where a TV transmitter should be built and how powerful it should be make assumptions about the quality of the aerial system in a typical house. Amongst these assumptions are: That the aerial in use is of high quality. Obviously this means that if you've got an old coat hanger and bent it round a bit, then its performance will probably be lower than that assumed by the planning people. Better to get a proprietary aerial made by a specialist manufacturer. You could look in Yellow Pages under 'TV and Radio Aerial'. You may also wish to satisfy yourself that you are dealing with a member of the Confederation of Aerial Industries (CAI).

Check that the aerial is placed at least 10 metres above ground level, this will generally mean that it is above the roof line. That the down-lead is of good quality. A piece of wet string, or some old flex is not the way to perfect reception. Once again, the higher quality of cable (i.e. the more expensive!) the better. Also try and avoid sharp bends in the cable. As with the actual aerial itself, the down-lead can deteriorate with time. Consideration should be given to replacement (or at least an inspection) after about 10 years, including the aerial terminal block, which could have started to corrode. It has been known for water to pour out of the bottom of the down-lead when the plug was removed!

Generally, there are a few things that viewers can do in order to pin down the cause of a particular problem.

  • It is usually a good thing if you can ask your neighbour(s) if they are getting the same problem that you are.
  • Are you getting the same problem on all the TVs in the house
  • are they using the same aerial?
  • Is the problem on all channels, or just one?
  • Is there a VCR/DVD in the aerial path to your TV
  • is that performing correctly?
  • Are you confident that the TV is tuned in correctly?

Specific problems and their possible causes:

Ghosting: This happens when your aerial receives more than one 'version' of the TV signal. Usually this occurs when, as well as the 'direct' line-of-sight signal, an additional signal from the same transmitter is received. This may be caused by a reflection from some large object such as a building, or the side of a hill or even a clump of trees. The reflected signal takes a longer path to get to your aerial, and so takes a longer time, thus arriving at the aerial slightly later than the original. This then is displayed on your TV as another, weaker picture, slightly displaced from the main picture. This is known as an 'echo'. The obvious way of removing this problem is to remove the cause. Simply bulldoze the offending hill or flat and all may be well. Alternatively a simpler solution may be to rotate the aerial away from the offending reflection. As you move the direction of the aerial away from the line of sight to the transmitter, the signal strength will start to deteriorate, but you may find that there is a particular direction where the main signal is still strong enough, and the reflected signal has reduced to such a level that it is no longer a nuisance. Alternatively, a longer aerial may solve the problem. The longer the aerial, the more directional it is. That is to say that it is less prone to picking up signals that are not straight in front of it. So this may also solve the echo problem. Or you could try both tricks.... It has been known to move the aerial to point directly at the reflection, and get rid of the main signal altogether, but this is unusual. Also you may want to try rotating the aerial slightly on its axis (if the mounting allows you to do this), as the polarisation (the direction that the signal waggles) of the reflected signal may have been affected. In extremis, it may be necessary to change to a different transmitter, but this may not always be possible. Your local TV dealer or aerial installer will be able to help you.

Noisy pictures: 'Noisy pictures' may sound a bit cock-eyed, but the same thing that produces 'shash' noises on the programme sound, also affect the pictures. The effect as seen on the screen is a sort of 'snowy' picture with little white dots appearing randomly all over the screen. This is caused by lack of signal strength at the aerial input to your TV. There could be many reasons for this: Transmitter fault Despite what may be the perceived case, transmitter faults are quite rare. When they do occur, they are (usually!) detected very quickly and rectified as soon as possible. OFCOM sets very high standards for transmitter performance, which we (and the other commercial broadcasters) have to maintain. Any such fault condition will not be permitted to continue for a moment longer than is possible.

An aerial defect: This could be the aerial being moved out of alignment by, for example, birds sitting on it and causing it to move. Or there could have been high winds which may also have moved it. Or it may just be corroding away such that the performance has started to deteriorate.

The downlead: This also could have started to deteriorate if it is a bit aged; included here is the actual connection to the aerial. It is important when installing an aerial that the terminal connector is adequately protected from the weather by sealing the connector box.

The transmission path: In the spring, there are occasions when the new growth of trees and the emerging of leaves can impinge on a previously good transmission path. Trees are a bit of a problem for TV transmissions, and should be avoided where possible. There are only three solutions: 1) lop the tree. Usually not possible/advisable. 2) Raise the aerial to overlook the tree. Can be expensive if a high mounting pole is required, and additionally care must be taken to ensure that the structure on which it is mounted is strong enough to take the extra loading. 3) Use a different transmitter - not always possible. Also in this category are new buildings or other structures that cut off the path.

Distribution systems: Aerial amplifiers, so called 'passive splitters', and distribution amplifiers can all have an effect on your reception. All of these systems need to have good quality connectors in order not to degrade the signal. Passive splitters in particular need to have quite a powerful signal from the aerial in order to adequately share it round the various outlets. Powered amplifiers can also deteriorate over time, and just reseating the connectors may render an improvement. If you live in a building with a communal aerial system, it may be worth checking with your neighbours to see if they are getting the same problem. If they are, then you will need to contact the person or organisation who is responsible for the upkeep of the building and report the fault to them. Even if they're not, there could still be a fault with the feed to your own wall socket.

Cable Companies: If you receive your signal from a cable company, then it is their responsibility to provide you with a signal of good quality, and you should contact them. They obtain their signals in the same way as ordinary viewers, either from a transmitter or from a satellite, and then redistribute them to their subscribers. If they tell you that it is a problem with the broadcaster, ask them what they (the cable company) are doing about it. Although the broadcasters are not responsible for the signal after it has been received by the cable company, clearly it is in everyone's interest to get any problem sorted out quickly. Therefore, when they report a problem to us, we will work with them as quickly as possible to help them resolve it.

Patterning: This can take many forms, though usually it appears as moving curved lines, the so-called 'herringbone' pattern, or as a series of white sparkly horizontal lines. Almost always, these are caused by interference. The curved (or sometimes diagonal) lines are caused by another transmission on a frequency the same as that which the channel you are watching is using. This is probably unintentional, and would be being produced by badly set up or maintained equipment being used by, for example, a less than totally meticulous local taxi firm or radio amateur or even a pirate radio station!

In these cases, the only action that can be officially taken is by the Ofcom, whose job it is to track down the sources of this type of interference. The white sparkly horizontal lines are usually caused by nearby electrical equipment that is not sufficiently suppressed. This could include 'fridges, washing machines, tumble driers etc. Deduction by elimination is the game here, switch off each item of domestic equipment in turn until the lines go away. Bear in mind that the cause might be next door!

Lack of picture/sound: This is clearly a terminal condition! Questions to be asked here are: Is the screen full of 'snow', or is it a clean black picture? This assumes of course that the set is actually switched on - it has been known! If the screen is full of snow, and the other channels are the same, then the chances are that there is an electricity supply problem at the transmitter affecting all channels. In these conditions, there is very little that can be done (except of course by the electricity supply company) but just sit back and wait. If the screen is clean black, then there is a fault with the supply of the picture before it gets to the transmitter. You can rest assured that we will know about this and will endeavour to fix it as soon as possible. This diagnostic ritual is somewhat complicated nowadays by the tendency of modern TVs to do their own thing when they lose an input. It may give a 'blue screen' or maybe the clean black screen mentioned above. On the up side, it may actually tell you what it thinks is wrong! More information and advice can be obtained from: OFCOM, Riverside House, 2a Southwark Bridge Road London, SE1 9HA Tel 020 7981 3040 www.ofcom.org.uk

For problems specifically to Channel 4 or related stations contact:

Channel 4 Enquiries, PO Box 1058, Belfast, BT1 9DU

Tel: 0345 0760191

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