In this way the nulls in the modulation sidebands fall at the position where the next carrier is located. This is done by spacing each one by a frequency equal to the data rate being carried. Interference between the carriers is prevented by making the individual signals orthogonal to each other. The carriers are spaced very close to one another. The system uses about 1500 individual carriers that fill around 1.5 MHz of spectrum. Called Coded Orthogonal Frequency Division Multiplex (COFDM) it is a form of spread spectrum modulation that provides the robustness required to prevent reflections and other forms of interference from disrupting reception. The other key to the operation of digital radio is the modulation system. This is implemented on some channels such as those used only for speech. Further reductions in data rate can be achieved by reducing the audio bandwidth.
By analysing the incoming audio and only encoding those constituents that the ear will hear the significant reductions can be made. Additionally if a strong sound is present on one frequency then weaker sounds close to it may not be heard because the threshold of hearing is modified. It is found that the ear has a certain threshold of hearing. To achieve these reductions the incoming audio signal is carefully analysed. The digital radio system adopted reduces the data rate down to 128 kbits / sec, a sixth of the bit rate for a similar quality linearly encoded signal.
For the system to be viable the data rate has to be considerably reduced from that of a standard CD.
The encoding and compression system is of paramount importance. There are two main areas of the system that are of interest in digital radio: namely the modulation system and the audio digital encoding and compression system. This consortium consisted of manufacturers, broadcasters research bodies and network operators. The technical standards for digital radio were developed under the auspices of the European Eureka Project 147.
Additionally the bandwidth required to accommodate a full stereo signal would need to be reduced to ensure efficient use of the spectrum. These would be delayed sufficiently for the data to become corrupted. One of the major problems was that many receivers would use non-directional antennas and as a result they would pick up reflected signals. Some existing digital techniques were investigated but it was realised these had significant limitations for this application. To produce a digital system that operates satisfactorily under the conditions required for digital radio a large amount of work was undertaken in the development stages.
Portable radio that can receive digital radio transmissions How DAB digital radio works With the facilities that digital radio offers it is now being accepted and listeners are switching to these new digital radio transmissions in the areas where they are available. It is also possible to have news scrolling across the bottom of the screen used on the radio.ĭAB digital radio is now well established in many countries around the world from the UK and Europe to Canada, Australia and many other countries. In this way it is possible to transmit the title of a track, and a picture of the artist whilst the some music is being transmitted. The digital radio signal carries data alongside the audio, and this enables text and images to be transmitted alongside the audio to enhance the listening experience. In addition to this many new services can be carried on these digital radio transmissions enabling the new system to be compatible with the 21st century. Also it does not suffer from the multipath effects often experienced on FM transmissions and as the system uses what it known as a single frequency network (SFN) there is no retuning required when moving from one coverage area to the next. People who have heard DAB digital radio have commented on the significantly better sound quality and "presence" of the new radio system. As the name indicates signals are broadcast in a digital format to enable CD quality to be achieved. What is DAB Digital Radio Tutorial Overview or tutorial giving information about the basics of what is DAB, Digital Audio Broadcasting, a form of radio broadcasting technology now used in a number of countries.ĭigital Audio Broadcasting, DAB Tutorial Includes:ĭAB Digital Radio, which is also known as digital audio broadcasting, is an entirely new system for broadcasting and receiving radio stations.