DAB is (DigitalAudioBroadcasting) shorthand, it offers near CD-quality sound, broadcast and business opportunities of additional data service, the listener can more easily listen to completely interference-free broadcast industry to lower launch costs to provide CD-quality programs to audience, will lead the receiver and transmitter industry opportunities, but also to promote the broadcasting sky towards multimedia broadcasting (DMB) in the world.
DAB is the second AM, FM broadcasting traditional analog broadcast the third generation – the digital broadcast signal, its appearance is a revolution in broadcasting technology. Digital broadcasting is immune to noise, interference, anti-wave propagation fading, the advantages for high-speed mobile reception, and so on. It provides CD-quality stereo sound quality, signal distortion is almost zero, can reach “crystal clear” enthusiast broadcast sound quality, especially for broadcast “classical music”, “Symphony”, “Pop”, etc., being extremely professional musicians, music enthusiasts and audiophiles sought after! But within the range of from multipath interference, in order to ensure that fixed, portable and mobile reception of high quality.
Sensual simultaneously “listening” technology
According to the popular saying, DAB is a product of the era of the migration to digital audio transmission arising from the analog era, it also came after AM and FM broadcasting system of the third generation. But even more interesting is that, relying on DAB, in theory, you can use the eye to “listen” to the broadcast – Because digital features, DAB can transmit any text or even an image signal. So you can connect DAB radio and television, in order to restore the digital signal in the video image.
DAB operating frequency in the choice of DAB working frequency is usually to consider, as frequency increases, the allowable distance between the launch pad to be reduced, so that the number of transmitters needed to increase the relationship between the square. (1) Band I (47 ~ 68MHz) in the band, due to the effect of ultra distance (E horizon) make the application received limited. In addition, in the band, especially the so-called “that noise”, such as subway interference for DAB, it is not the ideal working band. (2) Band II (87.5 ~ 108MHz) band is allocated to the terrestrial sound broadcasting use, it is now occupied by the FM radio. Obviously, DAB eventually be transmitted in the band. The band is not only assigned to sound broadcasting, and because it is close to 100MHz, for terrestrial digital sound broadcasting is particularly desirable. (3) The Band III band equally well suited for digital terrestrial sound broadcasting, particularly in the field test conducted DAB or implementation of the initial phase, for example, 233 ~ 230MHz Channel 12 television.
(4) Band IV / V (470 ~ 790MHz) in the UHF band, more than 80% for television coverage. If the synchronization network is small hive synchronization network, and the maximum driving speed is limited, then, UHF band for DAB, it is entirely possible applications. (5) L-band (1452 ~ 1492MHz) European Broadcasting Union (EBU) have pointed out that, with the work to cover the ground in the 1.5GHz range DAB digital synchronization network, although technically possible, but in the VHF (such as television Channel 12-Band compared to the number of transmitting stations to be 16 times larger, its running costs are also significantly higher, according to a rough estimate, about 4-fold to work when the VHF band. Further, in a car for a receiver, the system requires two antennas one for the VHF band, a band for 1.5GHz.L mostly for local coverage and small synchronous network. (6) S-band (2300 ~ 2600MHz) in order to achieve the same coverage and L-band, S-band to work on satellite transponder, the need for more power. at the same time, due to the higher masking, in the “shadow” region requires additional padding transmitter. in addition, due to the Doppler effect, so that these filler transmitters operate at the same frequency effectiveness is reduced. in general, the digital sound broadcasting in the S-band work is an expensive option, and provides only very limited technical possibilities.