1. Types of Digital Radio

2. Frequencies

3. DRM - Digital Radio Mondiale

4. Components of DAB and DRM Radio Signals

5. Public Access to DAB Radio Services

6. DAB Invention

7. DAB - Multiple Programmes in One Radio Signal

8. DAB in Europe

9. More Information

1. There are two systems:

• T-DAB (Terrestrial Digital Audio Broadcasting often called DAB)
• DRM (Digital Radio Mondiale - mondiale meaning worldwide in French)

Each system is incompatible and works with a different group of frequencies.

DAB is a replacement for FM broadcasting and DRM is a replacement for AM broadcasting.

Terrestrially broadcasted DAB covers local and national populations.  In the future satellite broadcasted DAB could cover several countries.

Terrestrially broadcasted DRM covers both national and international populations.

DRM unfortunately has the same initials as Digital Rights Management - a completely different topic.

2.  There are 73 DAB frequencies in three bands.

Each frequency occupies a wide bandwidth of 1.536 MHz.

The frequencies are also known as blocks and as ensembles (the French translation).

VHF means Very High Frequency.

VHF Band 2 is an existing public broadcasting band named as the 'FM Band' by the Americans.

Band 3 has 38 blocks 5A to 13F. In Britain VHF Band 3 was used for the former 405 lines public television service. Korea is different having a range from block 7A (175 MHz) to block 13C (214 MHz).

Band L has 23 blocks LA to LW.  Canada uses blocks numbers 1 to 23 with slightly different frequences.

Click here to see block frequencies.

3.  DRM is intended for frequencies less than 30 MHz. Its signal bandwidth is less then 10 KHz.

DRM is essentially an AM (Amplitude Modulation) signal. AM signals in short, medium and long wave bands can propagate vast distances compared to FM signals in VHF Band 2 (87 - 108 MHz).

The DRM Consortium was created when an agreement was signed on 5 March 1998 at Guangzhou, China. Their web site states:

• DRM is the only universal, non-proprietary digital AM radio system with near-FM quality sound.
• DRM will be extended to include existing broadcasting bands between 30 MHz to 120 MHz. Development and testing are expected to be completed by 2007-2009..

DRM is being used for radio broadcasts in the Long Wave band, in the Medium Wave band and in the Short Wave bands.  Because the signal is digital it is now possible to get stereo on previously mono-only wave bands.

Currently DRM is less popular than DAB.

4.  Because DAB is transmitted as ordinary computer data, the data can be audio, visual (picture and video) or computer files. DAB uses MPEG 1 and MPEG 2.

The bandwidth of the DRM signal is a tiny fraction of that of the DAB signal. The smaller signal capacity restricts the transmission of large amounts of data.

5.  DAB channels can be freely available to the public or restricted for private, governmental or commercial purposes such as subscription services. The access restrictions in DAB are very similar to those found with on satellite television channels.

6.  DAB was invited by an European Telecommunication Standards Institute committee called Eureka. It was their 147th project and they started work on DAB in 1987. That is why sometimes DAB is called Eureka 147.

In 1992 DAB was recommended by a technical committee of the World Conference of Broadcasting Unions. In 1994 it became an ITU standard. In March 1997 it became European standard ETS 300401.

7.  Unlike analogue radio signals when one radio signal is one radio programme, DAB programmes are transmitted in a group with several other programmes. Because the DAB signal is digital (meaning in a format which can be understood by computers) the electronics in the DAB radio easily separate those signals into individual programmes.

This is why the bandwidth of a single DAB broadcast signal is about 1.5 MHz wide.

One DAB radio signal or one block (in French, un ensemble) can contain about 6 high quality stereo music channels or as many as about 20 lower quality monaural (mono) speech channels.

DAB uses the same 'several channels in one signal' system used on satellite television broadcasts. (in satellite television vernacular the blocks are known as transponders).

If the broadcaster reduces the data rate on a channel then the audio quality will deteriorate. For good quality music a high data rate is necessary. For speech a much lower data rate will suffice.

The data rates per channel can vary between 8 kbit/s and 384 kbit/s.

8.  Most of Europe uses DAB Band 3 but La République Française & Der Bundesrepublik Deutschland use mainly Band L.

Britain has been allocated Band L blocks for future use. The Band L block for Slough, Windsor & Maidenhead is LD (1458.096 MHz) and

the reference code is G__00004.

9.  Some very interesting colourful PDF leaflets about DAB are available from:

www.worlddab.org/images/eureka_leaflet.pdf (4 pages)

www.worlddab.org/images/eureka_brochure.pdf (24 pages)

Lots of interesting technical details are available from

http://www.wohnort.demon.co.uk/DAB/index.html