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Digital radios are a far cry from the old-fashioned crystal radio sets of yesteryear. They can pick up and decode radio stations using digital transmissions and are reckoned by some to be the future of radio broadcasting as we know it.
A good question. The problem with AM radio is that it's not very good quality. In the US, you can have stereo AM radio, but even that's not too good as reception quality can vary.
FM radio's better as it doesn't suffer as badly from atmospherics overnight. However, it is difficult to tune into, and needs a good aerial and a strong signal to get rid of the background 'hiss'.
With both the current normal broadcast formats (and even shortwave format), listeners need to know the frequency that a station broadcasts on to find it. Without that frequency, you're lost. Enter digital radio...
What it Does
It's actually quite clever. By allocating space on a multiplex (a transmitter broadcasting more than one station at a time on the same frequency), each station can have as much space as it needs. So a talk station can get away with a mono, 64K data stream, whereas a classical music station could get a decent stereo 256K data stream or even higher.
Cleverer still, stations can use the space they've been allocated to split themselves in two. BBC Radio 5-Live, a sports station in the UK, currently broadcasts a football commentary on Saturday afternoons on medium-wave, but broadcasts two separate commentaries on digital radio, just splitting the station in two. At the end of the commentary, the stations just join together again as one data stream. And you never even noticed.
The coding is made especially for people on the move, so that you can listen under bridges and all the dodgy areas you've never had decent radio reception before.
Digital radio is currently broadcasting across the UK.
So Where can I get the Receivers from?
This is where you need to be clever. A digital radio, according to those who work in electrical shops, is one with numbers on the front instead of a dial. This is not a digital radio. A digital radio is one that probably says DAB (Digital Audio Broadcasting) on the front of it, and costs around £5001. New technology doesn't come cheap, although there are plans to bring out cheaper digital radios soon, and computer attachments, so you can hear the stations on your PC.