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Guidelines for Improving Digital Television and Radio Reception |
1
Terrestrial television and radio aerials
1.1
General
1.2 Life expectancy
1.3 Direction and polarisation
1.4 Television aerials
1.5 DTT picture degradation
1.6 Set-top aerials
1.7 Separation between aerials
1.8 DAB aerials
2
Amplifiers
2.1
General
2.2 Masthead amplifiers
2.3 Setback amplifiers
2.4 Distribution amplifiers
3
Coaxial feeder cable
3.1
General
3.2 Fixing and routing of coaxial cable
3.3 Sharing of coaxial down leads
3.4 Termination of coaxial cables
4
Receiving equipment
4.1
DTT receivers
4.2 Digital satellite receivers
4.3 Digital radio receivers
5
Recording equipment
5.1
Video recording and playback equipment
5.2 Other associated equipment
6
Solving reception problems
6.1
General
6.2 Digital co-channel interference
6.3 General interference
6.4 Finding the source of interference
6.5 Remedies
7
Effects due to a lack of immunity
7.1
General
7.2 Use of filters and ferrite RF chokes
7.3 Video recorders
7.4 Cable television
7.5 Satellite television
Annexes
Annex
A: Sources of information
Annex
B: Glossary
This publication provides guidance to television and radio dealers, service engineers and aerial installers on dealing with interference to digital television and radio reception. Similar guidance has been produced for analogue television and radio interference in information sheet RA 323 'Guidelines for Improving Television and Radio Reception', available from us (see Annex A).
Other guides on achieving good digital reception are available, principally the R-Books produced by the Digital Television Group (see Annex A). The specific aim of this document, however, is to provide information on the best way to avoid the potentially damaging impact of interference, which can come from a wide range of radio frequency (RF) sources.
The Radiocommunications Agency (RA) is responsible for investigating television or radio interference problems resulting from the use of unauthorised radio transmitters or faulty electrical equipment. If such a source is suspected, viewers and listeners can seek our guidance by completing the form in leaflet RA 179 'Television and Radio Interference' (see Annex A).
In appropriate cases we will carry out a specific investigation. However, experience has shown us that many cases of interference are caused by inadequate or faulty aerial installations, resulting in a poor signal to the receiver, and/or defective or deficient receiving apparatus. As these are the responsibility of the householder, we will direct viewers and listeners toward their dealer if we find that the interference is caused by problems within the installation. These guidelines aim to help dealers avoid such problems during installation, and to resolve them if they occur on existing systems.
We have produced this publication with assistance from the British Broadcasting Corporation (BBC), the Confederation of Aerial Industries Ltd (CAI), the Digital Television Group (DTG), Independent Television, the Independent Television Commission (ITC), Intellect, the Radio Society of Great Britain and York EMC Services Ltd. It describes the most common types of interference along with possible solutions, and should assist the radio and television trade in not just resolving interference to digital reception but also, through good installation practice, avoiding interference in the first place.
1. Terrestrial television and radio aerials
Terrestrial television
and radio services are planned primarily for receivers that use directional
aerials installed outside the building, ten metres above ground level. All viewers
and listeners, no matter how close they live to the transmitting station, are
advised to
use an outside aerial, with attenuator if necessary, to achieve optimum interference-free
reception (if planning conditions permit).
For digital radio, as with analogue radio, simpler aerials often provide satisfactory results, making portable and mobile reception possible. However, simpler aerials are more likely to suffer from interference, and RA will not usually be able to assist if problems arise. A similar situation applies to digital television, but here there is even stronger emphasis on the use of an appropriate roof-mounted aerial.
Please note that many existing transmitter sites delivering analogue television do not carry digital terrestrial television (DTT) signals. Where they do, the viewer's existing receiving aerial may not be satisfactory for receiving DTT services and may therefore need to be changed.
There are planning restrictions on outdoor aerials in some areas. Where this is the case, the best alternative is a loft aerial, although generally it will not offer such robust reception; this is mainly due to the reduced height of the aerial and the attenuation of the signal through the roofing material. Some concrete tiles, for example, can reduce UHF television signals by as much as 20 dB because of their high metallic content. A set-top television aerial is far less likely to be satisfactory; the signal it receives will be considerably poorer than that provided by a rooftop aerial and it will be far more prone to receiving interference.
Aerials and cable deteriorate with time, causing sudden or gradual loss of the signal. Aerial systems generally last for seven to ten years. A number of factors affect the life of an aerial system, including:
In cases of poor reception on an existing aerial system, the strength of the signal should be checked using the appropriate test equipment at the receiver.
1.3 Direction and polarisation
The aerial should be mounted using the appropriate polarisation, and directed towards the transmitter that provides the best reception. Broadcast organisations such as the BBC, the DTG and the ITC supply data on the appropriate transmitter to use. Reception of signals from other transmitters outside the service area may be possible, but the quality of service is unlikely to be good and cannot be guaranteed.
The directionality of an aerial may not always be enough to achieve good reception. Vertical and lateral positioning may be needed; a cranked arm-mounting pole can be useful in these circumstances.
Aerial quality is a key factor in achieving and maintaining good, interference-free reception. The recommended type of aerial is one that meets a recognised standard of quality and performance, such as the CAI Aerial Benchmark (see Annex B).
The measured signal strength at the termination of the down lead should be 45 to 65 dBµV for DTT (and 60 to 80 dBµV for analogue), measured with a suitable DTT meter for DTT signals. To allow for variations in signal strength and to ensure optimum results, the signal strength for both analogue and DTT should be 6 dB above the minimum recommended level.
Consistent results cannot be expected if the minimum signal level falls below 45 dBµV on DTT multiplexes (i.e. a group of services transmitted to a single channel). However, care must be taken to ensure that the analogue levels do not exceed 80 dBµV, or the DTT receiver may display 'lock-up' or picture failure. Excessive signals may require the use of an attenuator.
The existing aerial may not be suitable for the group of DTT channels intended for reception. Specific channel-group aerials should be used, except where diverse channels are used to cover all the available multiplexes.
Unlike analogue reception (which suffers gradual degradation), DTT reception is subject to a number of different effects, as explained in Section 6 of these guidelines.
DTT reception does not generally suffer from ghosting, but sudden picture degradation may occur in extreme circumstances due to signal reflections. RA 323 'Guidelines for Improving Television and Radio Reception' contains more information (see Annex A).
All television services are intended to be received using an external aerial. A set-top aerial can give good reception in some conditions but is not recommended. Please note that RA will not visit householders to investigate complaints of television interference where an external aerial is not being used (although we will consider investigating if the local authority does not allow external aerials to be installed).
1.7 Separation between aerials
If more than one aerial is to be mounted on a single pole, the aerials should preferably be mounted one above the other and at least one metre apart (with the exception of those configured as a 'phased array').
Digital audio broadcasting (DAB) services are delivered in the UK in Band III (between 217.5 and 230 MHz), with many services provided as part of a 'single frequency network' (SFN).
DAB aerials can be either omnidirectional or directional types. Directional (i.e. 'Yagi' or similar) aerials are generally recommended only in areas of low signal strength, where high gain is necessary to achieve an adequate signal. In other areas, an omnidirectional type is preferable because it will allow reception from more than one transmitter forming part of the SFN; it is a feature of SFNs that more than one transmitter can contribute constructively to the received signal.
All DAB transmissions are vertically polarised, so care should be taken to ensure that the mounting pole does not impair the performance of vertically mounted aerials.
Amplifiers can generally be classified into three categories: masthead amplifiers, setback amplifiers and distribution amplifiers.
Used carefully, amplifiers can resolve particular reception problems – but indiscriminate use can sometimes make matters worse. The wide bandwidth of many amplifiers may cause them to amplify both wanted and unwanted signals, with resultant interference effects. Excessive amplifier gain will also overload the equipment. An amplifier should be selected for the specific installation, and may need to be used in association with attenuators and/or filters. Ideally, amplifiers should be screened and low-noise, and connectors should be of a suitable quality (e.g. F-type connectors).
In some situations, such as with a long cable run, a masthead amplifier can give a worthwhile improvement to reception. It should be used only where the off-air signal meets the required DTT reception minimum at the aerial, and after every effort has been made to increase the signal level by other means (such as adjusting the location of the aerial or using an aerial of a higher gain).
The amplifier should be mounted as close as possible to the aerial while avoiding feedback problems. The amplifier gain should be the minimum required to overcome the cable losses. Care should be taken not to overload amplifiers.
Setback amplifiers are readily available and easy to install, so they are often perceived as a simple means of improving reception. However, they should be used with care. As the amplifier is at the bottom of the aerial down lead, it is unlikely to give much improvement to a weak signal because it also amplifies the noise. This type of amplifier is frequently broadband, so is susceptible to problems resulting from cross-modulation etc.
Broadband distribution amplifiers supplying multiple outlets can amplify unwanted signals outside the television or sound broadcast bands. In locations where there are strong signals from broadcast or other types of transmitter, use of a channelised amplifier and/or a suitable filter may be necessary. If any of the amplifier outlets are unused, it is important to ensure that they are correctly terminated.
With some types
of coaxial cable, the braid contains insufficient copper to form an effective
shield. This can allow unwanted signals (e.g. from nearby radio transmitters)
to pass through
the braid, possibly resulting in interference.
Inadequate shielding can cause interference to terrestrial television reception if a satellite television installation nearby has used the incorrect type of cable. With the developments taking place in digital broadcasting, it is imperative that tape and braid cables are properly connected and meet a recognised quality standard (at least the standard CT100, i.e. the CAI Cable Benchmark).
3.2 Fixing and routing of coaxial cable
To avoid premature deterioration of coaxial cable:
For further information, refer to the CAI Codes of Practice (see Annex A).
3.3 Sharing of coaxial down leads
Diplexers, splitters and combiners allow FM radio, digital radio and terrestrial television to share the same down lead, but they introduce an additional loss (typically up to 2 dB). They may also introduce signal ghosting from unwanted reception on the second out-of-band aerial. Con-sequently their use should be avoided, particularly where signal strength is low.
The down lead(s) from a satellite dish must use a separate cable, and must not be connected to a terrestrial aerial system.
A satellite receiver generally contains a broadband amplifier. If a television signal from a terrestrial aerial is fed to a television receiver via a satellite receiver and a video recorder, the overall gain may be excessive, leading to cross-modulation and increased susceptibility to out-of-band signals.
Where a DTT receiver is in place, it should be the first device in the RF chain if possible. More information is available in the DTG installation guides (see Annex A).
If a satellite receiver and/or DTT receiver is used in conjunction with a video recorder, the two/three RF output frequencies must be on different UHF channels. A spacing of at least two channels should avoid patterning effects.
3.4 Termination of coaxial cables
Two types of coaxial cable termination exist for radio and television reception systems:
These connectors should be correctly fitted, with care, to the coaxial cable in accordance with the manufacturer's instructions.
DTT receivers take several forms, including (but not necessarily limited to) the following:
Generally, these guidelines apply equally to either of the above types of receiver, although the method of operating them may differ.
If reception is poor, the tuning of the television channels should be checked to ensure that they are correctly set for the local transmitter. The precise method for programming the correct local channels will vary according to the type of receiver, but will generally involve an auto-search procedure.
If the signal strength meter shows an adequate signal level but the television picture is poor, the television equipment may be faulty; alternatively, this may be a symptom of interference. For DTT, a meter capable of measuring digital power must be used. This meter should be programmed to indicate whether the required margins, given in Section 1.4, are being obtained.
If signal levels are strong, or a higher-gain aerial is already installed to reduce ghosting for analogue services, overload may occur in the television. Overload of analogue television normally causes patterning and sometimes line tearing or effects similar to co-channel interference; in the case of DTT, it causes reception problems. In such cases, an aerial attenuator should be tried.
4.2 Digital satellite receivers
The most likely cause of poor digital satellite reception is a problem with the dish antenna or its low-noise block (LNB). If the signal strength meter shows an adequate signal level but reception is poor, the receiver may have lost sensitivity due to a tuner fault or a damaged input socket. A signal strength meter in the receiver itself should be used with care.
Overloading of the receiver front-end is extremely unlikely in satellite systems. If it proves necessary to attenuate the signal to the receiver, the device used must provide a DC bypass for the power supply to the LNB.
Digital terrestrial radio in the UK uses the digital audio broadcasting (DAB) system. Currently the signals are transmitted in Band III between about 217.5 and 230 MHz. However, in the future it is likely that DAB will also be transmitted in L-Band at around 1.5 GHz.
Digital radio receivers generally fall into three categories:
The issues of reception in vehicles are beyond the scope of this publication, which will deal only with the first two categories.
DAB national services, and most individual regional and local services, use a single frequency network (SFN); all transmitters for a particular multiplex transmit on the same channel. The system is designed to operate in situations where signals are received simultaneously from a number of transmitters, without destructive interaction between them. England and Scotland use different channels for independent national radio services, so around the Scotland/England border it is necessary to check that the receiver is tuned to the most appropriate channel.
If signal levels are adequate but reception is poor, the receiver may have lost sensitivity – due to a tuner fault or a damaged aerial socket, for example.
Reception problems can also occur if signals are too strong – because the receiving location is very close to the transmitter, for example. Fitting an attenuator between the aerial and the receiver may provide a solution. Care is needed, however, because national and local networks are not always transmitted from the same locations; the signal from the transmitter providing one service could be very high and tend to overload the receiver, while the signal providing the other service is quite low. Using an attenuator to deal with the stronger signal may render the weaker signal unusable, so it may be appropriate instead to use two separate directional aerials. This approach enables the signals from the two sites to be managed independently; an attenuator can be used on the aerial feed delivering the stronger signal without introducing attenuation of the weaker signal, which also benefits from the gain offered by the aerial directivity.
5.1 Video recording and playback equipment
Many video recorders
contain an RF amplifier, which provides a loop-through feed for the television
receiver RF outlet. Where television signals are strong, the television may
suffer
cross-modulation interference, so an attenuator or filter may need to be fitted
to the video recorder aerial input. (Some video recorders contain a switchable
attenuator for this purpose.)
While an RF inter-connection between the video recorder and the television may be acceptable, a fully screened SCART cable is the preferred method for inter-connection. If an RF inter-connection to the television is unavoidable, the video recorder output channel should not be tuned to any local channel. If interference is experienced, the output channel may need to be adjusted. (Interference is particularly likely to occur in areas where the television channels used for broadcasting are one, five or nine channels above or below the video recorder output channel).
A SCART cable contains several different signal cables within its outer cover. For best results, all the signal cables should be individually screened to prevent the signals from being induced into another conductor (causing the main picture to appear in the foreground while the interfering signal appears as a floating picture moving in the background; moving patterns can also result). Equipment suppliers recommend using the SCART lead supplied with the product; if this is not possible, a similar or better-quality individually fully screened cable must be used.
5.2 Other associated equipment
If a camcorder, video game or other equipment is frequently connected via the television aerial socket, we recommend the use of a coaxial changeover switch to avoid possible damage to the socket. The switch must have adequate isolation to reduce the level of the signal fed from the video game or camcorder back to the aerial. To prevent the signal from being re-radiated from the aerial, the signals must not be combined. The DTG leaflet 'Connectivity Guidelines for Installers and Manufacturers' contains more information (see Annex A).
If reception problems arise, a suitably qualified person should check the installation to ensure that the recommendations in the previous paragraphs have been followed.
Even though the signal strength may be adequate, many different sources of interference can affect the reception of digital broadcast services. However, unlike interference to analogue services (where it is usually possible to identify the type of interference by the nature of the effect), different types of interference to digital services usually have the same effects:
Observing how often the interference occurs and whether it is related to other events (for example, the switching of central heating thermostats) can provide the only clues to the cause of the interference.
6.2 Digital co-channel interference
Co-channel interference occurs when signals are received not only from the wanted transmitter but also from one or more distant transmitters operating on the same channel. It can degrade the bit error ratio of a DTT multiplex until the failure threshold is exceeded, resulting in prolonged loss of picture.
Co-channel interference can occur in any area, due to unusual atmospheric conditions that cause television signals to travel much further than normal; such conditions can last for several hours or days. Television broadcasters sometimes make announcements about co-channel interference on analogue services when this effect is present, but such an approach is less helpful on digital services where, in some circumstances, interference can cause a total loss of service. The use of directional aerials may help.
Digital radio and television services are particularly susceptible to wide-band impulsive noise generated by a variety of electrical systems, including switches and thermostats in heating systems, refrigerators and ignition systems for oil and gas boilers. Inadequately suppressed electric motors used nearby, such as those in hair dryers or electric drills, can also cause interference, as can a bad connection anywhere in the mains supply to a television or radio (a loose wire or fuse in the mains plug, for example, or a loose connection in a multiway adaptor).
Although the impulsive interference may last for only a fraction of a second, the disturbance to the radio or television service may take a few seconds to correct itself; if it lasts longer, the switch or thermostat may be faulty. Leaflet RA 272 'Problems Thermostats Can Cause to Television and Radio Reception' contains more information (see Annex A).
Overhead power, electric railway or tramway lines can be sources of interference, and can often radiate for considerable distances. Any metalwork can radiate interference, including ring-main wiring (especially on the 'earth' conductor, since a 50 Hz earth is not usually a good one at RF).
Electronic equipment (such as a computer or a satellite tuner) can sometimes cause radio or television interference if it is too close to a television or radio aerial.
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These sequences show the frame changes (at 25 frames per second) that can occur with digitally transmitted pictures. The interference-free signal at the top shows that the transition from fish to plants and the later transition from plants to fish is a clean cut. The next sequence has just enough white noise added to it to cause pixellation and blocking. The following sequences feature 1 dB more interference added in each case. All these sequences were recorded from a television supplied with the recommended minimum signal level at the aerial socket.
6.4 Finding the source of interference
If interference occurs frequently and for extended periods of time, electrical appliances in use within the house should be checked by switching them off in turn. Intermittent interference may coincide with a refrigerator, freezer, central heating system or time switch turning on or off.
If interference can also be heard on a portable analogue radio, it may be possible to use this to find the source – which may be in a neighbouring property, in which case the neighbour's co-operation will be required to find the source.
Electrical equipment has to meet certain levels of performance relating to emissions and immunity. Most electrical and electronic equipment marketed in the UK after 1 January 1996 must conform to the Electromagnetic Compatibility Regulations (Statutory Instrument 2372/1992) and carry the CE mark.
Older equipment may not have been designed to meet current standards, or may have developed a fault. If interference occurs, it may require modification or repair. For safety's sake, any repairs or modifications must be carried out by a suitably qualified person.
Television or radio receivers that carry the CE mark meet certain standards for immunity to unwanted signals, and will generally suffer fewer problems of unwanted breakthrough than those without the CE mark. However, the CE mark does not guarantee that no interference or breakthrough will occur – only that the equipment was compliant to a certain level when it was first placed on the market. In some circumstances, additional measures such as filtering may still need to be taken. Please note that:
If an indoor aerial is used, equipment that meets the relevant standards may still cause interference if it is too close to the aerial. It is also important not to install equipment near electrical wiring, which can carry interference over considerable distances.
7. Effects due to a lack of immunity
Problems sometimes occur because a broadcast radio or television receiver has insufficient immunity to unwanted signals. Broadcast radio or television reception may sometimes be affected by signals from other authorised radio users such as:
The effects of such signals on a DTT picture are similar to the effects of other types of interference (see Section 6), or of a poor signal caused by an inadequate antenna or faulty installation.
Different sources of interference affect digital services in similar ways, so it is difficult to deduce the source from the nature of the effect. The best way to establish the cause of interference is to observe what is happening in the vicinity. Is there, for example, a radio transmitting antenna nearby? If the interference can be detected on an analogue radio or an analogue television, this may give some clue to the source; portable analogue radios or televisions can be especially helpful in establishing the source.
If an AM transmitter is causing interference, the operator's voice may be heard. If a single side band (SSB) transmitter is the source, the audible effects will be a distorted, 'squawky' sound. A Morse code transmitter will give a rhythmic series of clicks or buzzes. FM transmitters do not normally give rise to audible effects.
If the interference is present only when a nearby transmitter is operating, the transmitter is not necessarily at fault; properly functioning licensed transmitters can give rise to interference in certain circumstances. The problem can often be solved by using a suitable filter at the aerial socket, or elsewhere on the affected installation, to improve its immunity to unwanted signals.
7.2 Use of filters and ferrite RF chokes
Most unwanted signals are at a lower frequency than the UHF television band, so a 'high pass' filter is required. If the unwanted signal is far below the UHF television band, a simple filter will normally be adequate; if it is close to the UHF television band (e.g. UHF pagers), a high pass filter with a sharp cut-off is required. It is important to ensure that any filters fitted are suitable for use with DTT.
Where a masthead amplifier or some form of distribution amplifier is used, placing a filter between the aerial and the amplifier may be necessary. The amplifier should also be in a screened box. We recommend fitting UHF-band pass filters, especially where amplification is used to distribute DTT signals within the home.
Unwanted signals may be picked up and coupled into the equipment by the braid of the coaxial cable, the mains lead or speaker cables, which act as an aerial. This type of interference can normally be suppressed by using a ferrite RF choke, which can be made by winding a length of the appropriate cable onto a suitable ferrite ring core. If the interference is coming via the mains lead, winding the mains cable of the affected equipment on a suitable ferrite ring core may be necessary.
If a video recorder suffers interference from a nearby transmitter, this should be tackled in a similar manner to television interference. Where there is a RF connection from a video recorder to a television, cables meeting at least the quality standard CT100 (i.e. the CAI Cable Benchmark) should be used. Sometimes a second filter or ferrite RF choke may be required at the input of the television.
Using an individually screened SCART connecting cable reduces the risk of interference to the analogue signal entering the VCR; this is the preferred way of connecting any devices equip-ped with this type of connector.
Problems of interference to cable television networks are the cable operator's responsibility to resolve. If a cable company requests assistance to cure an interference problem, RA may be able to offer advice on a commercial repayment basis.
Interference to satellite reception from nearby radio transmitters may be caused by interference into the RF output of the satellite receiver. This should be treated in a similar manner to video recorder interference.
Some satellite systems transmit in frequency bands used by other radio services (e.g. fixed-link and satellite communication services). As these bands are not reserved for broadcasting, the reception of these transmissions in the UK does not enjoy the same protection from interference as those in the broadcasting bands.
In most cases of interference to satellite reception, a suitable, well-shielded site for the installation needs to be found. The dish should be sited:
Given careful siting to maximise the separation angles between the directions of the satellite and the terrestrial source, the discrimination of the satellite receiving dish is usually adequate to rectify the problem. In some situations, the use of a larger antenna may solve the problem; please note that planning permission may be required in such cases.
8. Physical reception problems
Trees, hills and other obstructions such as buildings, cranes, gasometers, football stadiums and wind farms may cause reception problems as they can obstruct or reflect signals. While there is usually no legal requirement to rectify a loss of television or radio service caused by such developments (unless such a condition is included in the planning consent), much can be done to an installation to alleviate matters.
Planning authorities and developers are encouraged to contact the BBC and the ITC to determine whether a proposed development will cause reception problems. The siting of satellite receiving aerials is particularly important, as trees and other obstructions can completely block the signals.
Moving objects such as cranes, gasometers and rotor blades on wind farms can also affect reception.
The influence of trees can be seasonal, and evergreen trees affect television signals more than deciduous trees. Rain and wind can vary the effects of trees on reception, by causing ghosting and signal strength fluctuations. In areas where television signals are strong, it is often possible to accept some attenuation from trees and still obtain a satisfactory picture. If this is not the case, the possibility of re-siting the aerial should be investigated; otherwise, pruning the trees may be the only solution. In all instances, allowance should be made for growth in height and spread of the trees. Any remedial work should be by agreement with the tree owner and within the statutory controls; failure to observe the requirements of the Town and Country Planning Acts could result in a fine up to £20,000. Information about trees, their management and the law affecting trees is available from the Arboricultural Advisory and Infor-mation Service's Tree Helpline (see Annex A).
Annex A: Sources of information
Radiocommunications
Agency (RA)
Wyndham House
189 Marsh Wall
London
E14 9SX
Tel: 020 7211 0211
Email: library@ra.gsi.gov.uk
RA staff can advise members of the public who think that interference to their domestic television and radio reception is caused by the unauthorised use of radio or faulty electrical apparatus. If we judge it to be appropriate, we organise a visit; no charge is made for this unless the problem is found to be caused by deficiencies within the television or radio installation or other apparatus in the complainant's home. To request RA assistance, householders should complete the form in leaflet RA 179 'Television and Radio Interference', available from the above address.
The following documents are also available:
RA 206 'Addresses of the RA Local District Offices'.
RA 272 'Problems Thermostats Can Cause to Television and Radio Reception'.
RA 323 'Guidelines for Improving Television and Radio Reception – advice to the trade on dealing with interference to analogue television and radio reception'.
Arboricultural
Advisory and Information Service (AAIS)
Alice Holt Lodge
Wrecclesham
Farnham
Surrey
GU10 4LH
Tel: 01420 22022
Email: admin@treeadviceservice.org.uk
Website: www.treeadviceservice.org.uk
Part of the Tree Advice Trust, the AAIS provides information on trees, including their effects on television reception.
British Broadcasting
Corporation (BBC) Reception Advice
Television Centre
Wood Lane
London
W12 7RJ
Tel: 08700 100 123
Email: reception@bbc.co.uk
Website: www.bbc.co.uk/reception
BBC Reception Advice can provide advice on aerials, reception problems and services from DTT, DAB and digital satellite.
Confederation
of Aerial Industries Ltd (CAI)
Fulton House Business Centre
Fulton Road
Wembley Park
Middlesex
HA9 0TF
Tel: 020 8902 8998
Email: office@cai.org.uk
Website: www.cai.org.uk
The CAI is the recognised body representing companies from all sections of the television and radio signal distribution industry. It can provide members of the public with the names of local aerial installers who are CAI members.
Digital Action
Plan
Email: digitaltelevision@culture.gov.uk
Website: www.digitaltelevision.gov.uk
The Government's digital television website sets out Government policies for digital television and provides answers to frequently asked questions. Documents available online include:
Digital Television Action Plan.
Digital TV Information for Landlords.
Digital Television
Group Ltd (DTG)
Liss Mill
Liss
Hampshire
GU33 7BD
Tel: 01730 893144
Email: office@dtg.org.uk
Website: www.dtg.org.uk
The DTG represents all aspects of the television industry in the implementation of digital television. It is a trade association that has expanded its activities to encompass retailers and installers of consumer equipment. DTG publications include:
Connectivity Guidelines for Installers and Manufacturers.
R-Book 2 'A Guide to Domestic DTT Aerial Installations'.
R-Book 4 'Integrated Reception Systems for Digital TV'.
Independent Television
Commission (ITC) Technology Information
Staple House
Staple Gardens
Winchester
SO23 8SR
Tel: 01962 848647
Email: technology@itc.org.uk
Website: www.itc.org.uk
The ITC can provide technical information about all UK commercial television: ITV (Channel 3), Channel 4, Channel 5, S4C, multichannel terrestrial, cable and satellite television.
Intellect
Russell Square House
10-12 Russell Square
London
WC1B 5EE
Tel: 020 7331 2000
or 020 7395 6700
Website: www.intellectuk.org
Intellect is a trade association with more than 1,000 members from the information technology, telecommunications and elec-tronics industries in the UK.
Radio Authority
Holbrook House
14 Great Queen Street
London
WC2B 5DG
Tel: 020 7430 2724
Email: info@radioauthority.org.uk
Website: www.radioauthority.org.uk
The Radio Authority licenses commercial radio stations and can provide a composite list of transmitter locations and associated parameters.
Radio Society
of Great Britain (RSGB)
Lambda House
Cranborne Road
Potters Bar
Herts
EN6 3JE
Tel: 0870 904 7373
Email: GM.Dept@rsgb.org.uk
Website: www.rsgb.org.uk
The RSGB represents the amateur radio community and can give advice on interference problems associated with amateur radio.
| CAI Aerial Benchmark | A standard specification that describes the parameters necessary in a UHF antenna to enable reliable digital terrestrial reception. The benchmark defines the level of performance and characteristics needed to attain certification by the Confederation of Aerial Industries (CAI) as a product suitable for digital applications. |
| CE Mark | A mark, containing the letters 'CE' in a specific format, which may be affixed to a product, its packaging or instructions. The CE mark is a declaration by the manufacturer that the equipment complies with all applicable European Directives. In the context of this document, the Electromagnetic Compatibility Directive 89/336/EEC is of particular relevance. |
| Channel | A dedicated frequency on which a broadcast takes place. |
| DAB | Digital audio broadcasting (digital radio). |
| DTT | Digital terrestrial television. |
| Frequency | The number of complete cycles of an event (in communications, typically an alternating-current signal) per unit of time. The standard frequency unit is the Hertz, named after an early German investigator of the properties of high-frequency alternating-current waves. |
| Immunity | The ability of a piece of electronic equipment or a system to operate in the presence of electromagnetic signals. |
| Impulsive noise | A term describing the clicks from central heating boilers, washing machines and light dimmers in the home, which can cause a flash on analogue televisions in marginal reception conditions and, with digital reception, may cause blocking, freezes and high-pitched clicks on sound. |
| Multiplex | A group of services transmitted in a conventional 8 MHz RF channel. |
| RF | Radio frequency. |
| SCART | Standing for Syndicat des Constructeurs d'Appareils Radio Recepteurs et Televisieurs, this is a 21-pin connector (also known as Peritel or Euroconnector) used on television sets, video recorders, satellite receivers etc to provide a direct audio and video connection. |
| SFN | Single frequency network, e.g. DAB. |
| SSB | Single side band – a type of radio modulation, often used by radio amateurs. |
Further copies of this document are available from:
Information and
Library Service
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London E14 9SX
Tel: 020 7211 0502/0505
Fax: 020 7211 0507
Enquiry Point: 020 7211 0211
| RA 415 December 2002 |
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