Exploring Science Frontiers

Marconi and DAB

   Who was Marconi?

Marconi as a very smart young man!    In 1895 Italian inventor Guglielmo Marconi built the equipment and transmitted electrical signals through the air from one end of his house to the other, and then from the house to the garden. These experiments were, in effect, the dawn of practical wireless telegraphy or radio.

   Marconi was born in Bologna, Italy.His father was Italian, his mother, Irish. He was educated first in Bologna and later in Florence. Then he went to the technical school in Leghorn, where he studied physics.

   Following the successes of his experiments at home, Marconi became obsessed with the idea of sending messages across the Atlantic. He built a transmitter, 100 times more powerful than any previous station, at Poldhu, on the southwest tip of England, and in November 1901 installed a receiving station at St. John's Newfoundland.

   On December 12, 1901, he received signals from across the ocean. News of this achievement spread around the world, and he was acclaimed by outstanding scientists, including Thomas A. Edison.

   Marconi received many honors including the Nobel Prize for Physics in 1909. He was sent as a delegate to the Peace Conference in Paris in 1919, in which capacity he signed the peace treaties with Austria and Bulgaria.

Why is he important?

   Not even Guglielmo Marconi could have imagined where his early obsession with Heinrich Hertz's electric waves would end. In 1894, aged 20, much to his parent's amazement he sent the first radio waves across their attic to ring a bell. By the time he died, in 1937, Marconi had fine-tuned these early experiments into the worldwide system of radio that keeps the world talking today.

The first radio!    Exactly a century after the first radio broadcasts flickered through the ether, a new invisible signal has begun to buzz above our heads in the shape of digital audio broadcasting (DAB). I

   So exactly what's behind this latest high-tech acronym? Well, DAB is to radio what the CD was to the record industry - it drags the antiquated AM/FM broadcasting system into the digital age of crystal-clear, studio-quality transmission. Ordinary or analogue radio broadcasts need something called a 'carrier frequency' which, as the name suggests, carries the varying signal which stores the music or speech of the programme. Each different radio station needs a different carrier frequency. To broadcast Radio 1 in FM across the whole of Britain, you need to carry it on several different frequencies covering different parts of the country. This is why you need to re-tune to keep listening when driving up and down the country. In contrast, DAB relies on a single block of frequencies known as a 'multiplex' to carry not just one service, but several, allowing nationwide access to all the current BBC radio stations on one narrow band of frequencies.

   So how is this achieved? Firstly, the sound is compressed, reducing the amount of information that needs to be transmitted. This is done by a system called MUSICAM, which discards the sounds that will not be heard by the listener, such as very quiet sounds that are drowned out. The remaining information is just packaged more neatly using a compression algorithm. Compression algorithms look for patterns in data and then gather together all the identical parts to send them in one group. Compression algorithms process data in the same way that a supermarket check-out processes your groceries: if you are buying four tins of tuna, the check-out operator will scan only one tin and then type in '4'. Reducing the amount of information in this way allows more efficient use of the radio spectrum.

   Such compression techniques have been around for a while, so what's so new about DAB? Well, digital broadcasting promises interference-free listening - no more crackles and drop-outs when you drive under a bridge or behind a building. Such continuous reception is guaranteed by splitting the signal across 1,536 different carrier frequencies, so even if some frequencies are affected by interference, the receiver is still able to recover the original sound from the others.

   But the problems of DAB weren't solved that easily. The feeds from London all leave Broadcasting House simultaneously, but by the time they reach the transmitting sites via different routes they are no longer synchronised. To resynchronise them to within 5 microseconds (one two-hundredth of a second) it's necessary to use timing pulses from 24 satellites 10,000 miles above Earth.

   So are all these extra complications really necessary? Would Marconi be turning in his grave or rejoicing at an innovation that carries his concept into the twenty-first century?

   By totally re-thinking the way in which information is transmitted, listeners will not only get interference-free reception and studio-quality sound, their radio sets will be more user-friendly, with easier tuning - and they might even be able to receive text and other useful data. Other possibilities include in-car navigation systems, and displays of maps, accessed by linking radios to computers. And in addition to transmitting the heart of BBC Radio's output - Radios 1, 2, 3, 4 and 5 Live - the BBC will be broadcasting extra programmes including live proceedings from the House of Commons, commentary from a range of sporting events and programmes from the BBC World Service. BBC NOW is another innovation that will be available to DAB listeners as a result of this exciting technology. To be launched in the middle of next year, it will offer an instant information service. Just turn on your radio and you'll hear a ten-minute loop tape of the latest news stories. Some radio receivers will also have a special chip inside them that will store the latest ten-minute report, allowing you to fast-forward through the stories yourself to find the item you want.

   These are exciting times for a technology that really hasn't changed since Marconi's early experiments in that Italian attic in Bologna. DAB has the potential to change the way we use the radio. But one thing that isn't likely to change is the word 'radio'. Accurate as the acronym 'DAB' is, it's not likely to catch on in place of 'radio'. The DAB Times is unlikely to appear on the shelves shortly! Further information from DAB, Room 509, BBC, Henry Wood House, London W1A 1AA.

   Note: Although Marconi is credited with the invention of radio he was inspired by Heinrich Hertz, who first demonstrated the reality of radio waves in 1886. Michael Faraday had predicted the existence of electromagnetic radiation in 1831, mathematically analysed by James Clerk Maxwell by 1855. Sir Oliver Joseph Lodge transmitted the first radio signals in August 1894 at the same time as Alexander Popov was doing similar experiments, but Marconi acquired the world's fastest radio patent. Apparently, history remembers the fastest with the paperwork!


IMPORTANT NOTE: In accordance with Title 17 U.S.C. section 107, this material is distributed without profit or payment to those who have expressed a prior interest in receiving this information for non-profit research and educational purposes only.


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