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Guidelines for Improving Analogue Television and Radio Reception

Guidance for dealers, engineers and aerial installers on achieving good, interference-free analogue television and radio reception

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Contents
Foreword  
   
1. Aerials for terrestrial television and radio
1.1 General
Life expectancy
Direction and polarisation
Television aerials
Ghosting
1.6 Set-top aerials
1.7 FM radio aerials
   
2. Amplifiers
2.1 General
2.2 Masthead amplifiers
2.3 Setback amplifiers
2.4 Distribution amplifiers
   
3.
3.1 General
Fixing and routing coaxial cables
Sharing coaxial down leads
3.4 Terminating coaxial cables
   
4.
4.1 Low sensitivity
Cross-modulation
   
5.
5.1 Video recorders
5.2 Other associated equipment
   
6.
6.1 General
Television co-channel interference
6.3 FM radio
Long wave (LW) and medium wave (MW) radio
6.5 Short wave (SW) radio
Broadband interference
6.7 Electrical interference
6.8 Finding the source of interference
6.9 Remedies
   
7.
7.1 General
7.2
Video recorders
Cable television
7.5 Satellite television
7.6
Other non-radio equipment
Other obstructions – trees
   
Annexes  
Annex A: Information and assistance
Annex B: Filter suppliers
Annex C:

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Foreword

This publication provides guidance to television and radio dealers, service engineers and aerial installers on dealing with interference to analogue television and radio reception. Similar guidance has been produced for digital television and radio in leaflet RA 415 ('Guidelines for Improving Digital Television and Radio Reception'), available from the Radiocommunications Agency (RA) – see Annex A.

The specific aim of this document 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. 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.

If appropriate, 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 householder's responsibility, 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), Independent Television, the Independent Television Commission (ITC), Intellect and the Radio Society of Great Britain. Describing the most common types of interference along with possible solutions, it should assist the radio and television trade to resolve interference to analogue reception – and, through good installation practice, to avoid interference in the first place.

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1. Aerials for analogue terrestrial television and radio

1.1 General

Terrestrial television and FM sound broadcast services are planned for receivers that use directional aerials installed outside the building, ten metres above ground level. All viewers and listeners, however close they may live to the transmitting station, should use an outside aerial (with an attenuator if necessary) to achieve optimum interference-free reception.

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 types of roof tiles can, especially when wet, reduce UHF television signals by as much as 20 dB.

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 – see Section 1.6.

1.2 Life expectancy

Aerials and cables 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, check the signal strength using the appropriate test equipment at the receiver input.

1.3 Direction and polarisation

The aerial should be mounted using the appropriate polarisation, and directed towards the transmitter that provides the best reception. Broad-casting organisations can supply data on the appropriate transmitter to use – see Annex A. Reception of signals from other transmitters outside the planned service area may be possible, but the quality of service is likely to be inconsistent and cannot be guaranteed.

Changing 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.

1.4 Television aerials

Overall aerial quality is a key factor in achieving and maintaining good 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 C.

Ideally the measured signal strength at the termination of the down lead should be 60 to 80 dBµV, measured with a signal strength meter. To allow for variations in signal strength and to ensure optimum results, the signal strength should be 6 dB above the minimum recommended level. If the signal strength is weak, a picture similar to Figure 1 may be received.

The picture should be ghost-free and with error-free teletext. The type of aerial required to achieve this depends on local conditions such as the distance from the transmitter and the presence of hills and neighbouring buildings. In coastal areas, more directional aerials may be needed to reduce the effects of co-channel interference – see Section 6.2. In areas with low signal strength, a higher-gain aerial system with low-loss coaxial cable is preferred to a masthead pre-amplifier.

A few remote areas of the UK are outside the service area of any television broadcast transmitter. Within a transmitter's service area, there may be small areas that suffer poor reception due to the local terrain or obstructions. Do not use a wide-band aerial unless it is actually required; such aerials are more susceptible to receiving signals outside the desired frequency range, and generally have poorer performance. The aerial must be suitable for the group of television channels intended to be received.

1.5 Ghosting

Ghosting (see Figure 2) is the result of a reflected television signal. The reflection can be from:

Slight ghosting can cause problems with teletext reception and subtitling. It can also affect Programme Delivery Control (PDC), as this is a teletext-based service. In some circumstances, ghosting may affect NICAM reception. You may be able to reduce the ghosting by repositioning the aerial or, in some situations, by using a different design/style of aerial (for example, a more directional aerial or a log-periodic). Eliminating ghosting on all channels may not always be possible.

The use of a cranked arm-mounting pole may also help. If multiple aerials are to be mounted on a single pole or close together, they should preferably be mounted one above the other and at least half a metre apart (except those configured as a 'phased' array).

1.6 Set-top aerials

All television services in the UK are intended to be received using an external aerial. A set-top aerial can give good reception in some conditions but is not recommended. RA will not visit householders to investigate complaints of television interference unless a correctly installed external aerial is being used (other than in areas where external aerials are not permitted).

1.7 FM radio aerials

For good, noise-free stereo reception, use a directional aerial of at least two elements, incorporating a balun. This should preferably be mounted outside, as loft-mounted aerials give variable results. A signal of 48 to 64 dBµV is required at the termination of the down lead. A separate coaxial feeder should be used for the FM aerial. If the FM receiver has a connection only for a 300 ohm balanced feeder, a 75 to 300 ohm balun transformer must be used at the input to the receiver.

Most broadcast transmitters use mixed polarisation, which helps with reception on car and portable radios. Aerials may be mounted either horizontally or vertically; horizontal polarisation is preferred, since it is less prone to multipath reception. However, in severely screened locations a vertically polarised aerial can receive a much stronger signal; up to 16 dB improvement has been measured. Many network 'filler' and local radio stations use vertical or mixed polarisation, so the elements of the aerial must be mounted appropriately. The use of dipole or circular (halo) type aerials is not recommended, although these may offer a convenient compromise close to the transmitter. Omni-directional aerials suffer from low gain, and are liable to multipath reception and consequent distortion.

Some remote areas of the UK are outside the service area of any FM broadcast transmitter. Even within a transmitter's service area, there may also be small areas that suffer poor reception due to the local terrain or obstructions. If the FM aerial is mounted together with a television aerial, they should be mounted at least one metre apart.

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2. Amplifiers

2.1 General

There are three general categories of amplifier: masthead amplifiers, setback amplifiers and distribution amplifiers. Used carefully, amplifiers can resolve particular reception problems – but indiscriminate use can make matters worse. The wide bandwidth of many amplifiers may cause them to amplify both wanted and unwanted signals, leading to interference. 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).

2.2 Masthead amplifiers

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 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).

Mount the amplifier as close as possible to the aerial while avoiding feedback problems. The amplifier gain should be the minimum required to overcome the cable losses. Take care not to overload the amplifier.

Even in well-engineered aerial installations constructed from quality products, considerable interference can occur with any masthead amplifier that also operates outside its specified frequency range. Certain mobile telecommunications installations occupy frequencies quite close to those used by UK television broadcasters. The problem can be particularly acute where a television aerial with an additional masthead amplifier is oriented towards a broadcast transmitter on a similar bearing to that of the telecommunications mast. 

The unwanted cross-modulation effects (shown in Figure 3) can sometimes be minimised by using a fully screened amplifier, constructed in well-shielded housing that incorporates F-type cable connections. This type of amplifier is now widely available, albeit at increased cost. The use of UHF-only amplifiers will also help to minimise out-of-band interference. If using such amplifiers does not resolve the problem, you may need an additional purpose-made filter to remove the interfering carrier. For best results, fit the filter close to the amplifier input. If a fully waterproofed filter product is unavailable, you may need to move the screened amplifier from the masthead itself to a nearby sheltered location within the roof space.

2.3 Setback 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 improve a weak signal much because it also amplifies the noise. This type of amplifier is frequently broadband, so is susceptible to problems resulting from cross-modulation etc.

2.4 Distribution amplifiers

Broadband distribution amplifierssupplying 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, you may need to use a channelised amplifier and/or a suitable filter. If any of the amplifier outlets are unused, make sure that they are correctly terminated.

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3. Coaxial feeder cable

3.1 General

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 causing interference.

Inadequate shielding can cause interference to terrestrial television reception if a satellite television installation nearby is using the incorrect type of cable. With the developments taking place in digital broadcasting, it is vital 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 coaxial cables

To avoid premature deterioration of coaxial cable:

For further information, refer to the CAI Codes of Practice (see Annex A).

3.3 Sharing coaxial down leads

Diplexers, splitters and combiners allow FM radio, digital radio and digital 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. Consequently 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, causing cross-modulation and increased susceptibility to out-of-band signals.

3.4 Terminating 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.

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4. Television receivers

If reception is noisy or there is ghosting, check the tuning of the channels (especially if autotuning was used) to ensure that they are set correctly for the most appropriate local transmitter. If the tuning is correct but the picture is noisy, measure the signal level from the aerial outlet using a suitable meter. If the levels of all relevant channels are found to be adequate, the most likely cause is a faulty receiver. Ghosting may also be caused by incorrect aerial alignment – see Section 1.5.

4.1 Low sensitivity

If reception is poor, check the tuning of the television channels (especially where autotuning has been applied) to ensure that they are set correctly for the local transmitter. If the signal strength meter shows an adequate signal level but the television picture is noisy, the television may have lost sensitivity – for example, due to a tuner fault or a damaged aerial socket (see Section 5.2).

4.2 Cross-modulation

If signal levels are strong or a higher-gain aerial has been used to reduce ghosting, cross-modulation may occur in the television. This normally causes patterning, and sometimes an unstable picture (known as line-tearing) or effects similar to co-channel interference – see Section 6.2. If cross-modulation happens, consider using an aerial attenuator.

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5. Associated home entertainment equipment

Many installations contain broadband amplifiers, through which the signal passes; these can amplify signals outside the broadcast bands.

5.1 Video recorders

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 – see Section 4.2 – so you may need to fit an attenuator or filter to the video recorder aerial input. (Some video recorders contain a switchable attenuator for this purpose.)

While an RF interconnection between the video recorder and the television may be acceptable, a fully screened SCART cable is the preferred interconnection method. If an RF interconnection is unavoidable, take care to choose a channel that is free of patterning effects. If interference is experienced, you may need to adjust the output channel. (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 being re-radiated from the aerial, the signals must not be combined.

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6. Solving interference problems

6.1 General

If reception problems arise, check the installation to ensure that the recommendations in the previous paragraphs have been followed.

6.2 Television co-channel interference

Co-channel interference occurs when signals are received from the wanted transmitter and from one or more distant transmitters operating on the same channel.

Co-channel interference from analogue television transmitters can cause line-pairing, which gives a fine 'Venetian blind' effect with horizontal and vertical bars. In more severe cases, it may be possible to see another picture 'floating' in the background, together with sync bars (see Figure 4).

Co-channel interference from digital television transmitters will give an even, structured 'grain' effect on analogue television pictures, looking rather like analogue noise. The stronger the received digital co-channel, the more pronounced the effect.

In some areas, co-channel interference may always be present unless an adequate aerial is used. The aerial must be sufficiently directional to reject unwanted signals that come from a different direction to the wanted signal, and those that have a different polarisation.

Co-channel interference can occur in any area due to unusual weather conditions (such as high atmospheric pressure), which can cause television signals to travel much further than normal. Such conditions can last for a considerable time.

6.3 FM radio

Unlike television transmitters, FM transmitters are not located together. It is often possible to use a single directional aerial whose beamwidth encompasses several transmitter sites. Omnidirectional aerials do not protect against unwanted reception of other stations sharing the same frequency. Transmitters broadcasting the same programmes to different geographical areas are grouped together in the same part of the FM band, so it is advisable to confirm that the correct transmitter is being received.

As with television co-channel reception, interference from unwanted stations may sometimes occur due to high atmospheric pressure. Under normal atmospheric conditions, particularly in coastal or fringe reception areas, the FM signal may at times fade or be affected by aircraft reflections. A more directional and higher-gain aerial will usually reduce these problems.

Some FM radio receivers may receive unwanted signals from non-broadcast commercial or other transmitters, including aircraft overhead. These transmissions are not in the FM band but may be heard due to the limitations of the affected equipment. The effects are also varied; unwanted signals may be strong enough to 'blank out' the wanted station temporarily, to appear as a whistle or to be heard as a
distorted voice. Improving the FM aerial and fitting a suitable bandpass aerial filterto the affected equipment will generally eliminate the interference. Under difficult reception conditions, switching to mono mode may be preferable.

6.4 Long wave (LW) and medium wave (MW) radio

Little can be done to reduce the effects of fading of AM radio signals in the LW and MW bands, particularly after dark. AM signals may suffer interference from sources such as:

Such interference can usually be reduced by adjusting the orientation of the receiver, so that the internal ferrite aerial is aligned for optimum reception of the wanted station. In other cases, moving the receiver further away from the source of interference may help.

In addition to the above sources, reception on these bands may be affected under adverse circumstances by broadband telecommunications systems using existing infrastructure as networks.

6.5 Short wave (SW) radio

The effects of fading are much more noticeable on SW broadcasting. This often results in a relatively low quality of service. Interference to SW signals can originate from all the sources listed above for LW and MW reception, or from wired distribution systems. As SW radio is used mainly to receive overseas broadcasts, it cannot be offered any protection from interference. Reception on the SW band can be greatly improved by using an outdoor aerial designed for the frequencies of interest.

6.6 Broadband interference

Generally, RA cannot investigate interference to LW, MW or SW broadcasting; however, interference suspected to be from broadband systems can be reported for possible investigation.

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6.7 Electrical interference

The effect shown in Figure 5 can be caused when an electric motor (e.g. in a hair dryer or an electric drill) is used nearby.

The effect shown in Figure 6 may be caused by switches or thermostats in heating systems, refrigerators or oil/gas boilers' ignition systems. Often, the interference lasts for a fraction of a second; if it lasts longer, the switch or thermostat may be faulty. Information sheet RA 272 ('Problems Thermostats Can Cause to Television and Radio Reception') contains more information – see Annex A. A similar effect can be caused by a bad connection in the mains supply to a television or radio, such as a loose wire or fuse in the mains plug or a loose connection in a
multi-way adaptor.

Overhead power lines, electric railways or tramways can cause interference, and can radiate for considerable distances. Any metal can re-radiate interference, including electrical wiring (especially the mains 'earth' conductor, since a 50 Hz earth is not usually a good one at RF).

Any electrical or electronic equipment (such as a computer or a satellite tuner) can cause radio or television interference if it is located close to a television or radio installation. This may result in a patterning effect on a television picture.

6.8 Finding the source of interference

If interference occurs frequently and for extended periods, check the electrical appliances within the house 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 be heard on a portable radio, it may be possible to use this to find the source – which may be in a neighbouring property, in which case you will need the neighbour's co-operation to find it.

6.9 Remedies

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, this equipment 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 interference problems than those without the CE mark. However, the CE mark does not guarantee that no interference will occur – only that the equipment was compliant to a certain level when it was first placed on the market. Additional measures such as filtering may still be needed.

Please note that:

If an indoor aerial is used, equipment that meets the relevant standards may still cause interference if it is close to the aerial. It is also important not to install equipment near electrical wiring, which can carry interference over considerable distances.

Coaxial cable should meet at least the minimum requirements of the CAI Cable Benchmark. Terminations must be the correct type to suit the cable, and must be made off correctly. The lead from the outlet to the television must be of a comparable standard to the down lead.

Television aerials should conform to a recognised standard of quality and performance, such as the CAI Aerial Benchmark. Aerials should be fitted externally. If the interference is entering the system via the aerial, using a higher-directivity aerial can help.

Avoid using outlet boxes if possible. If used, they should be screened.

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7. Effects due to the lack of immunity

7.1 General

Problems sometimes occur because the 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 television picture typically resemble Figure 7 and Figure 8, where a FM transmitter is being used. If an AM or SSB transmitter is being used, effects similar to Figure 9 and Figure 10 may be seen; also, the voice of the operator may be heard. Figure 11 shows the effect of mobile telephone interference.

Even if the interference is present only when a nearby transmitter is being used, the transmitter and its operation may not be at fault. The interference can often be removed 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

With television reception, most unwanted signals are at a lower frequency than the television band so a 'high pass' filter may help. If the unwanted signal is far below the television band, a simple filter will normally be adequate; if the unwanted signal is close to the required band, try using a high pass filter with a sharp cut-off. If a masthead pre-amplifier or other type of signal amplifier is used in the installation, you may need to place a filter between the aerial and the amplifier; the amplifier should be in a properly screened box. Do not fit any filter between the television set and the amplifier (where the amplifier is fed with DC up the coaxial inner cable) unless the filter is suitable.

Unwanted signals may be picked up and coupled into the equipment by the braid of the coaxial cable, the mains lead or other cables such as those connected to external speakers. 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, you may need to wind the mains cable of the affected equipment through a suitable ferrite ring core. Please refer to Section 2.2 regarding the susceptibility of amplifiers to interference.

7.3 Video recorders

If a video recorder suffers interference from a nearby transmitter, this should be tackled in a similar manner to television interference – see Section 7.2. If there is a RF connection from the video recorder to the television, use cables that meet at least the quality standard CT100 (i.e. the CAI Cable Benchmark). Sometimes a second filter or a 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, and is the preferred way of connecting between any devices equipped with this type of connector – see Section 5.1.

7.4 Cable television

Resolving problems of interference to cable television networks is the cable operator's responsibility. If a cable company requests assistance to cure an interference problem, RA may be able to offer advice on a commercial repayment basis.

7.5 Satellite television

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 similarly to video recorder interference – see Section 7.3.

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, using a larger antenna may solve the problem (but planning permission may be required).

7.6 Other radio equipment

Some types of radiocommunication equipment, such as cordless telephones and wireless baby alarms, are classed as 'unprotected radio services'. Users of such equipment cannot claim protection from interference, and should direct their complaints to the equipment supplier.

7.7 Other non-radio equipment

Signals from nearby radio transmitters may affect various types of electronic equipment that are not intended to receive radio signals. Common examples are:

Such equipment is defined as 'non-wireless telegraphy apparatus' and is beyond the scope of these guidelines. Interference complaints should be directed to the supplier.

7.8 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 Information Service's Tree Helpline (see Annex A).

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Annex A – Sources of Information

Please note that, subject to legislation, the Office of Communications (Ofcom) will take over the functions of the Radiocommunications Agency, the Independent Television Commission, and the Radio Authority (as well as the Office of Telecommunications and the Broadcasting Standards Commission) towards the end of 2003. Ofcom will be located at Riverside House, 2a Southwalk Bridge Road, London SE1 9HA. Tel: 020 7981 3000. Website: www.ofcom.org.uk

Radiocommunications Agency (RA)
Wyndham House
189 Marsh Wall
London
E14 9SX
Tel: 020 7211 0211
Email: library@ra.gsi.gov.uk
Website: www.radio.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 by 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:

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 the coverage areas of BBC radio
and television transmitters.

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 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:

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 electronics 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.

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Annex B – Filter suppliers

Aerial Techniques
59 Watcombe Road
Southbourne
Bournemouth
BH6 3LX
Tel: 01202 423555
Fax: 01202 425055
Website: www.aerial-techniques.com

Alban Electronics Ltd
6 Caxton Centre
Porters Wood
St Albans
Herts
AL3 6XT
Tel: 01727 832266
Fax: 01727 810546
Website: www.albanelectronics.co.uk

Dial Electrical/Electronics
Windsor Court
East Grinstead House
East Grinstead
West Sussex
RH19 1XB
Tel: 01342 326972

Radio Society of Great Britain
Lambda House
Cranborne Road
Potters Bar
Herts
EN6 3JE
Tel: 0870 904 7373
Fax: 0870 904 7374
Website: www.rsgb.org

AKD
Unit 5
Parsons Green Estate
Boulton Road
Stevenage
Herts
SG1 4QG
Tel: 01438 351710
Fax: 01438 357591

Cirkit Distribution Ltd
Park Lane
Broxbourne
Herts
EN10 7NQ
Tel: 01992 444111
Fax: 01992 464457

Maplin Electronics PLC
Valley Road
Wombwell
Barnsley
South Yorks
S73 0BS
Tel: 0870 264 6000
Website: www.maplin.co.uk

Waters & Stanton PLC
22 Main Road
Hockley
Essex
SS5 4QS
Tel: 01702 206835/204965
Website: www.wsplc.com

These are the names and addresses of some manufacturers of filters, but it is not intended to be an exhaustive list and there are undoubtedly other suppliers.

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Annex C – Glossary

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 its 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.
Cross-modulation
The modulation of a desired signal by an undesired signal. This is a special case of intermodulation (the mixing of two or more signals, producing additional signals at related frequencies).
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.
Interference
An unwanted disturbance caused by the signal from a radio transmitter entering a piece of electronic equipment that has insufficient immunity.
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.
SSB
Single side band – a type of radio modulation, often used by radio amateurs.
'Venetian blind' effect
A regular pattern of horizontal lines on a television picture caused by co-channel interference. These may be coarse or fine, depending on the relative frequency offset of the interfering source, and may vary between channels.

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RA 323 R4
July 2003
RA Homepage