[HCDX] Dabbling In DAB

[Mukesh Kumar <thecosmosclub@xxxxxxxxxxx>]

Dabbling In DAB

DAB presents one of the most exciting developments in
radio broadcasting in recent times. With AIR gearing
up to launch this digital service, this dream is
surely close to becoming a reality. 

Radio is an old-age companion to mankind. In the last
decade, there have been many developments in radio
broadcasting, and it is on the verge of a digital
convergence. There had been quite a few formats on
air, and certainly a few more will come up till one or
more of them becomes world standard in radio
broadcasting.
In India, the first digital broadcasting was stated in
the DAB (Digital Audio Broadcasting) format, closely
followed by the digital satellite radio service by
WorldSpace. The (Direct-to-Home) services for TV also
carry digital radio broadcasts, and probably, in a few
years, DRM (Digital Radio Mondiale) will make its
presence-free.
  DAB ? the most advanced technology in radio since
the introduction of FM stereo ? provides
interference-free reception and high quality sound,
easy to use receivers and an unlimited potential for
wider listening through many additional stations,
services and developments. If we listen to FM radio in
the car, there are hisses and plops as we drive along.
That is caused by multipath interference when the FM
signal bounces off buildings, trees and hills and
arrives at our receivers out of phase with the main
signal, confusing the transmission. 
But in the DAB receiver, there is a processor that
sorts through the myriad multipath signals and other
distortions t6o enhance the main signal. The means
that even in the most difficult listening
environments, like the centre of the city of the
high-rise buildings, the DAB signal remains perfect. 
As the third generation radio, the DAB system is
paving the way for the digital era of broadcasting.
This system was developed by the Eureka 147 project ?
an international consortium of broadcasters, network
operators, consumer electronic industries and research
institutes. They came together to develop the DAB
standard, which is currently being implemented
worldwide.
DAB is broadcast on terrestrial networks, with
prospects for satellite broadcasting in the future.
DAB can be received used a just tiny non-directional
stub antenna. High quality radio programs can also be
received in cars without any annoying interference and
signal distortion. DAB can carry audio, text,
pictures, data and even video to some extent. DAB
complies with the tough requirements of the digital
age emerging before us.
DAB can be transmitted on frequencies from the FM band
(88-108 MHz), but the services that have been
introduced in Europe, Canada and Australia, together
with pilots in India, are using other frequencies.
Some countries, including UK, are using Band III
(around 221 MHz), formally used for black and white
television signals. Others like Germany and Canada are
using L-Band (1452-1492 MHz).
DAB receivers currently in the market can receive both
Band III and L-Band transmissions. In 1992, the World
Administrative Radio Conference, he internationally
recognized meeting that assigns all the world radio
spectrum usage, allocated the L-Band frequency range
to digital broadcasting, both terrestrial and
satellite.
All DAB receivers will have digital displays including
some with large liquid crystal screens, and
broadcasters will have the option to transmit
additional Program Associated Data (PAD). On the
broadcast front, DAAB requires a fragment of the power
otherwise required by the analog broadcasting for the
same coverage area. Over three hundred million people
around the world can now receive more than 585
different services. Commercial DAB receivers have now
been on the market since 1998. There are more than 32
different DAB receivers commercially available abroad.
      All India Radio started regular experimental DAB
transmission in New Delhi in April 1997. AIR will be
launching a pilot DAB service with 1 kW transmitter in
Delhi this year. The transmission shall carry 6 stereo
channels in addition to PAD and Data Services. The
pilot DAB will be extended to Chennai, Mumbai and
Kolkata by the year 2005-06.

(From ?AV MAX? ? a monthly publication on audio visual
technologies.)

Regds.
Mukesh Kumar
Muzaffarpur
INDIA


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