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How DAB works

Generation of the DAB Signal

Each service signal is coded individually at source level, error protected and time interleaved in the channel coder. The services are then multiplexed in the Main Service Channel (MSC), according to a pre-determined, but adjustable, multiplex configuration. The multiplexer output is combined with Multiplex Control and Service information, which travel in the fast Information Channel (FIC), to form the transmission frames in the Transmission Multiplexer. Finally, Orthogonal Frequency Division Multiplexing (OFDM) is applied to shape the DAB signal, which consists of a large number of carriers. The signal is then transposed to the appropriate radio frequency band, amplified and transmitted.

Fig.1: Generation of DAB Signal

Reception of a DAB signal

The DAB ensemble is selected in the analogue tuner., the digitised output of which is fed to the OFDM demodulator and channel decoder to eliminate transmission errors. The information contained in the FIC is passed to the user interface for service selection and is used to set the receiver appropriately. The MSC data is further processed in an audio decoder to produce the left and right audio signals or in a data decoder (Packet Demux) as appropriate.

The WorldDAB Forum is an international non-government organisation whose objective it is to coordinate the implementation of all Eureka-147-based technologies, such as DAB, DAB+ and DMB.

Help receiving TV and radio

DAB stands for Digital Audio Broadcasting. It is a digital radio service which is broadcast from a UK-wide network of transmitters.

It uses digital technology which enables broadcasters to package together several radio stations; this is called multiplexing. Multiplexed radio stations are then broadcast on single frequency networks. This is an efficient way to provide lots more radio stations using fewer radio frequencies.

The BBC operates its own multiplex which is used to distribute all of its national Network radio stations. It rents space on commercial multiplexes to distribute Nations and Local radio stations.

DAB has allowed the BBC to broadcast digital only radio services. These include 6 Music and Radio 4 Extra. It has also allowed us to broadcast World Service in the UK and given the whole of the UK access to services such as Asian Network.

DAB multiplexes

We bundle a number of radio services together, before we broadcast them, into what is known as a multiplex. Your DAB radio can then pull out each individual radio service from the multiplex. To understand the differences between the BBC’s own DAB multiplex and the commercial multiplexes used for Nations and English regions services, see our DAB multiplex guide.

Single Frequency Network

We broadcast our DAB multiplex using the same frequency (12B) from a network of transmitters, which is why we describe it as a Single Frequency Network (SFN). This differs from FM broadcasting for example, where a radio station is broadcast using an individual frequency from each transmitter.

An SFN is beneficial to listeners if they are able to receive signals from more than one transmitter. The DAB radio will combine all the signals and make the reception more robust. It is also a more efficient use of spectrum and uses less electricity compared with analogue radio transmission.

Electronic Programme Guide (EPG)

In the DAB multiplexes we also add some additional service data. If your radio has the function, it allows you to see the schedule of services on each radio station, the same way you can on televisions.

Related articles

  • What is a good DAB installation?
  • What is a DAB multiplex?
  • What type of aerial do I need?

Related faqs

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Use our problem assistant to help you diagnose problems with reception and interference

Check the status of the transmitter you are using and find out TV and radio channels and frequencies

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DAB FAQs

Why am I unable to receive Local Radio, or National Radio such as BBC Radio Scotland, on my DAB Radio?

The BBC’s local and national radio services are carried on local commercial DAB Multiplexes. Please see our help page to see how DAB multiplexes work, Therefore, you may not be receiving this service, as there is not a commercial DAB service in your local area. To check what coverage of DAB services are available in your locality, please see our Transmitter checker tool.

My DAB reception has started to drop out, is this due to poor reception?

Firstly, poor reception might be down to poor coverage, so it is best to check you are in a DAB coverage area. Use our transmitter tool, which will tell you what national and local DAB services are available in your locality.

Secondly, If you are in a good coverage area, and are still receiving poor DAB reception please try our Problem Assistant for further advice.

How can weather affect DAB reception?

DAB reception is rarely disrupted by high-pressure weather conditions, but under some circumstances, signals from very distant transmitters can cause reception to break up, or be lost for periods of time. If you suspect this – particularly if you are also getting interference on FM – wait until the weather changes.

Where can I find Radio 5 Live Sports Extra & Radio 4 LW on DAB and when does it broadcast?

5 Live sports extra is a secondary service of Radio 5 Live, and not always available on air. When the BBC has additional sports content, it can be found next to Radio 5 live on DAB radio. This is similar to Radio 4 LW on DAB, which can be found next to Radio 4 on the list of stations. For more information on finding and storing these services, see our Help guide on DAB secondary services. The 5 Live Sports Extra schedule is available online, and Radio 4 LW on DAB, broadcasting Yesterday in Parliament, along with the Daily Service each day on their respective websites.

Can LED Lights Interfere with my DAB Reception?

There is a possibility some LED Lights can cause interference to DAB and FM Radio Reception, particularly if LED lights are used to replace halogen lights, and retain the original transformer. This is because the power used is lower, and is forced to work outside of its normal operating parameters, resulting in electrical impulse interference. For more information on interference, please see our RTIS site

DAB Help Guides

What is a good DAB installation?

Your radio must be in a good DAB coverage area to receive BBC services. Have a look at our Transmitter Checker to see what BBC services you can receive where you are. If you live in a basement flat, or your building is steel-framed or reinforced concrete, coverage may be affected.

Tuning

Most DAB radios can be tuned easily at the touch of a button. Sometimes a full scan is required. Portable radios should be tuned in a location in your home where the best possible signal is received. Most DAB radios come with built in signal strength meters which can be helpful. From time to time radios should be re-tuned in order to discover new stations.

Telescopic aerials

Telescopic aerials on portable radios should be fully extended to receive a good signal. Tilting and swivelling the aerial will help to get the best signal. Broken aerials may affect reception.

Outdoor aerials

An externally mounted aerial can be attached to many types of DAB portable radio and hi-fi systems. DAB aerials are different from FM or TV aerials, so you need a good quality DAB-specific aerial. An indoor aerial may be good enough, but for the best reception use an outdoor one. Ideally, this should be on the roof or high up on the outside of the building, though it may also give good results in the loft.

Cables and Connectors

If you have an external aerial, a radio signal will always lose some of its strength as it passes along the cable and through the connectors. It is important to minimise the loss by using good quality cable and connectors.

DAB radio in cars

DAB uses different frequencies from FM radio. We advise you check that your antenna is able to receive DAB, in the majority of cases you will need a new antenna. An exception is “helically wound” FM aerials. See our guide on DAB radio in cars

Qualified Installer

The BBC cannot recommend individual Installers. The CAI ( Confederation of Aerial Industries ) is a recognised trade body which will can put you in touch with one of their members in your area.

Troubleshooting DAB reception

Transmitter faults

By using our Transmitter Checker, you can check which DAB radio services are available at your location. It will also show you any transmitter faults. Currently it reports on network DAB stations only; Local and Nations radio faults are not included.

Works and Warnings

Check whether there are any known works or warnings that might be causing the problem.

Tuning

DAB uses multiplexes to group services together. The BBC network stations, e.g. BBC Radio 1, BBC Radio 4 are grouped together in a single multiplex. Nations and Local radio services are carried on a mix of commercial multiplexes.

Try switching your radio on and off. If you still have a problem use the ‘autotune’ function to re-tune. If this does not work, a full re-scan might be needed. Check your radio manual for specific instructions on doing a full re-scan. Further information on tuning your DAB radio can be found by visiting the Get Digital site or see our DAB tuning guide.

Portable Radios

Ensure the telescopic/integrated aerial is fully extended. Try moving the radio around to see if you can find a better position where you get good reception of all the stations you want to listen to.

In most circumstances the supplied telescopic aerial should be perfectly adequate, and as a rule of thumb DAB aerials tend to work best when vertical and extended at least 35 cm. If your radio reception is poor then you could consider an external aerial for best reception quality. Even in good areas an external aerial will guarantee optimum performance and will also ensure consistent listening quality.

Many Digital radios have a signal strength display which enables you to position the Radio for the best reception (usually a number of blocks) as a guide of reception quality. Unfortunately, some radios are less sensitive than others and need careful positioning to work reliably. If your radio displays signal strength, use this as a guide to ensure the best position.

Our DAB installation guide provides further information.

External aerials

It is important to check the cables and the aerial for damage and that they are operating correctly. Make sure any cables between your radio equipment and aerial are connected securely. For further information see our DAB installation guide.

Damaged Cables

Water can get into external cables and can cause reception problems. To rule this out see our guide on water damage to cables.

Car Radios

Radio reception can drop out when on the move due to changes in topography. See our car radio guide for more information.

Weather

Radio signals can be affected by fine weather including high pressure. The only solution is to wait for the weather to change, you should not re-tune during this time. Our information on h ow clear skies and fine weather can affect your radio reception may be useful, please see our weather guide.

Lost reception of one or more station within a multiplex

If all other stations are working ok and you have just lost one station. The problem could be due to a number of reasons, the station may have stopped broadcasting or have moved multiplexes rather than a radio fault. All of the stations in one multiplex should be behaving the same way.

​​​​​​​ Interference

If you are still having problems, it is possible an unwanted signal is the cause. For information on the symptoms of interference see our sister website RTIS .

Qualified Installer

The BBC cannot recommend individual installers. The CAI ( Confederation of Aerial Industries ) is a recognised trade body which will be able to put you in touch with one of their members in your area.

DAB radio in the car

To listen to DAB in your car you will need to ensure your aerial is able to receive a DAB signal. You may need to contact your car manufacturer to check. However, helically wound FM aerials are able to receive DAB.

The best place to put a DAB aerial is on the roof of the car and as far from the engine as possible, to avoid any interference.

If your car radio is showing no signal or no service for a station you usually receive, this could be down to one of the following things:

DAB Transmitter Fault

If you know your location, you can use our transmitter checker to see whether there is a problem. If not, then check the radio and the aerial to confirm they are working correctly.

Interference

Poor DAB reception can also be caused by equipment used in the vehicle. For example, phone chargers or dash cams sometimes cause interference and affect your radio signal. Try unplugging the items to see if one of them is causing any interference.

Retuning & DAB Pre-set Stations

If you have bought a new car, the DAB radio may be tuned to DAB stations in a different location. Delete the presets and re-tune to the services in your area.

Topography

When travelling in the car, your signal can be affected by natural features of the land, for example, hills, valleys, rivers, etc. The signal should return once you move away from these features.

Part time radio services on DAB

Where can I find them?

When Radio 5 Live Sports Extra is on air, you should find it right next to 5 Live on the list of stations on your digital radio. The same is true for Radio 4 LW on DAB. It can be found next to Radio 4 on the list of stations.

When do they broadcast?

Radio 5 Live Sports Extra has a dynamic schedule. To see what is available when, the BBC keeps a schedule on the sport website. Radio 4 LW normally broadcasts Yesterday in Parliament, The Daily Service and the Shipping Forecast each day.

How to find these services

It is best to re-tune your radio when they are broadcasting, so it will store the station in its memory.

Who is responsible for my Shared/Communal Aerial?

It is worth first checking to see whether the problem is with your own equipment, or the local transmitter. If neighbours are having the same problem it may be that the aerial itself is at fault, or there may be an interfering signal. In either case, you will need to ask your landlord or management committee to solve the problem.

Checking for problems

Check cables and leads within your property to ensure the problem is not a simple installation fault. Please see our Freeview Installation guide for further details.

To see whether there are any faults with the local transmitters use the BBC’s Transmitter Checker tool. This will help you to see if there are, or have been recently, transmitter faults in your local area.

Electrical interference

There are differences between a reception problem and one caused by electrical interference. See our help guides which explain the differences. Our sister site, the Radio and Television Investigation Service (RTIS) also has useful information on how to distinguish the difference.

If it is potentially interference, your landlord or management committee can contact the regulator, Ofcom, for help with solving the problem, using their contact web form. Since it is a communal aerial, you will not be able to contact Ofcom directly.

Freeview FAQs

Why does my television picture break up with tiny squares (pixellation), or is lost completely with a “no signal” message, when the weather warms up?

This usually happens in warm fine weather, where atmospheric conditions cause television signals to travel much greater distances than they normally would. As a result this can block or interfere with television signals from local transmitters, or the links between transmitters. For more information, please visit our page on how weather can affect your Television and Radio reception.

My Television reception is usually good in the day, so why does my television reception sometimes deteriorate in the evenings?

This may be due to two reasons. Firstly, you may have a poor aerial system, so we recommend you checking over your installation by reading our Good installation help guide . Secondly, you may be on the edge of Freeview coverage, and likely have a weak signal. This may be fine during the day, but in the evening, signals from distant transmitters can travel further, and can cause reception problems for those at the very edge of coverage. Use our Transmitter checker tool to see if you are in an area of good reception and for further advice.

Why are subtitles sometimes delayed or out of sync?

For programmes which are pre-recorded, we create the subtitles in advance. A technician uses the audio and picture to sync them with what’s happening on screen. For a programme broadcast live, (like the News), subtitles will be generated as it is broadcast, which is a complex and problematic process. This means you’ll often notice a delay when watching live programmes.

I have lost my BBC 4 HD after I have completed a retune. Why is this?

Following a decision by the Government, some channels used by Freeview, are being reallocated to allow for the future development of new mobile broadband services. This may mean some viewers will lose some TV services, or need to repoint/change their aerial. Contact the Freeview Advice Line on 0808 100 0288, or for further details please see Freeview TV Changes.

Freeview Help Guides

What is a good Freeview installation?

Aerials

There are all kinds of aerials available on the market and some which are specific to certain frequencies. A wideband aerial is a popular choice, although there are other aerials available. A qualified aerial installer with local knowledge will be able to advise further.

Height

Your aerial should be as high as possible pointing towards the transmitter with the best signal. Use the BBC’s Transmitter Checker tool to determine the best transmitter for your location. Ensure there is nothing in front of the aerial that could block the signal, such as trees. All TV reception predictions assume an outside aerial at a height of 10m from the ground.

Loft and indoor aerials

If you live close to a transmitter or can get a strong TV signal, then it could be possible to use an aerial in your loft or an indoor portable aerial. However, in both cases the signal will be weakened as it has to pass through various obstructions such as walls, roof tiles, foil backed insulation etc. Even if you are predicted to have good reception, you may have problems receiving services using indoor or loft aerials.

Cable and connectors

A television signal will always lose some of its strength as it passes along the cable and through the connectors. Therefore it is important to minimise the loss by using good quality cable and connectors.

Amplifier

These are not recommended unless absolutely required as they can introduce unexpected reception problems. See our help guide on the different types of amplifiers available .

Polarisation

Depending on the transmitter you are using, your aerial elements will need to be mounted flat (horizontal) or on its side (vertical). A qualified aerial installer with local knowledge will be able to advise further.

Qualified Installer

We cannot recommend individual installers. However the CAI ( Confederation of Aerial Industries ) is a recognised trade body which will be able to put you in touch with one of their members in your area.

Troubleshooting your Freeview Television reception

It is important to check that your installation is intact. For example all the cables between your television equipment and aerial are connected securely and none is damaged. Further information is available in our Freeview installation guide.

Check our Works and Warnings section to see whether there are any known problems.

Using our Transmitter Checker , check your transmitter is not undergoing any work.

Television signals can be affected by fine weather including high pressure (atmospherics) and the only solution is to wait for the weather to change, you should not retune during this time. See how weather can affect Freeview reception .

Trees

During wet weather, when covered in moisture, all trees can have an appreciable effect on signals. As trees sway in windy weather the screening effect varies, leading to fluctuations in the quality of reception.

Damaged Cables

Water can get into external cables and can cause reception problems. To rule this out see our guide on cables and water damage.

Manual Retune

A manual retune is more effective than an auto-retune as it only tunes your television to the transmitter your aerial is pointing towards. For more information on how to retune manually see our manual re-tuning page .

Interference

If you are still having problems, it is possible an unwanted signal is the cause. For information on the symptoms of interference see our other site, RTIS, for further information.

Qualified Installer

We cannot recommend individual Installers. However the CAI ( Confederation of Aerial Industries ) is a recognised trade body which will be able to put you in touch with one of their members in your area.

How to check your cables for water damage

  1. If possible, check the external cable for any signs of damage, such as cracking and tears. Damaged cables can cause reception problems and can allow water into your installation.
  2. Find the cable that goes from your aerial or satellite dish into your television, radio or set top box and unplug it. This may be from a socket on the wall or a direct cable through the wall.
  3. If you are using a satellite dish to receive your television, you will also need to check the LNB and cap for any signs of water damage. You may need to instruct a qualified installer to assist you with this.
  4. If it is a direct cable, check for any obvious signs of water or a green build-up on the connector. If it is from a wall socket check both the connector on the cable and on the wall socket for any signs of water or green build-up. A green build-up is a sign that water has at some point got into your installation.
  5. If you find water damage then it is likely that the cable will need replacing by a qualified aerial installer.

We cannot recommend individual installers. However the CAI ( Confederation of Aerial Industries ) is a recognised trade body which will be able to put you in touch with one of their members in your area.

How to better my signal using an amplifier or attenuator

When to use an amplifier

A signal amplifier should only be used as a last resort when the television signal is weak. Even the best amplifier will still add some noise to the television signal it is amplifying/boosting that could result in picture break up. A good amplifier should have a filter built in that only allows the signal you want to be boosted and not any unwanted signals. Otherwise, all the unwanted signals will also be boosted, which can cause pictures to break up.

Problems using amplifiers

Amplifiers themselves are a common source of reception problems. For example, if water were to get into a masthead type, they can start to boost the result of the fault. This could be unwanted signals and result in picture loss on your own television and, maybe, those living nearby. To check, remove the power from the amplifier and see whether the problem goes away.

There are three types of amplifier – masthead, set-back and distribution. All these need a power supply to work.

Masthead

These fit directly under an outside aerial and usually the best type of amplifier to fix weak signals.

Set-back

These fit between the aerial socket in the wall and your television.

Distribution

These split the TV signal from a single aerial and allow the signal to be sent to several different televisions in the building.

Some amplifiers are a mix of the above. For example, some masthead amplifiers are also distribution amplifiers. Some can also combine television and FM radio signals.

Attenuators

When to use an Attenuator

If you are experiencing pixellation or picture break up, it may be that your signal is too strong as this often presents itself similarly to a weak signal. This is likely to happen if you live close to a transmitter.

Attenuators can be used to decrease the incoming signal if it is too strong without distorting it. It is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, boosts the signal, an attenuator provides loss, reduces the signal. Attenuators are always a compromise and should only be used if absolutely necessary.

They come in a variety of powers; in most cases a small reduction is all that is needed. It may take a little trial and error to find the most suitable one for your installation, and it is worth taking the advice of a local aerial contractor to select the correct one for the installation.

Who is responsible for my Shared/Communal Aerial?

It is worth first checking to see whether the problem is with your own equipment, or the local transmitter. If neighbours are having the same problem it may be that the aerial itself is at fault, or there may be an interfering signal. In either case, you will need to ask your landlord or management committee to solve the problem.

Checking for problems

Check cables and leads within your property to ensure the problem is not a simple installation fault. Please see our Freeview Installation guide for further details.

To see whether there are any faults with the local transmitters use the BBC’s Transmitter Checker tool. This will help you to see if there are, or have been recently, transmitter faults in your local area.

Electrical interference

There are differences between a reception problem and one caused by electrical interference. See our help guides which explain the differences. Our sister site, the Radio and Television Investigation Service (RTIS) also has useful information on how to distinguish the difference.

If it is potentially interference, your landlord or management committee can contact the regulator, Ofcom, for help with solving the problem, using their contact web form. Since it is a communal aerial, you will not be able to contact Ofcom directly.

Additional radio services DAB has allowed the BBC to broadcast digital only radio services. These include 6 Music and Radio 4 Extra. It has also allowed us to broadcast World Service in the UK and given the whole of the UK access to services such as Asian Network.