TV over the radio? It's in the picture

You could be forgiven for feeling confused at last month's report that NTL and London-based Radioscape demonstrated the transmission of TV images to a PDA using a Digital Audio Broadcasting (Dab) signal.

Dab is set to replace analogue radio as soon as enough of us can be persuaded to buy the receivers.

This won't be very soon as, although early models have sold well, the cheapest is still around £100, 10 times the price of a cheap analogue set.

Dab channels have far less bandwidth than TV - around 200Kbps, only 20 per cent of which is allowed to be put to non-audio use.

So far this data has been used to transmit little more than programme details, but the possibilities multiply as receivers get more intelligent.

At last, one Far East manufacturer is developing a Dab-enabled handheld computer which could also pack two-way links such as GPRS/3G and Wi-Fi.

Three factors make these 'Dab handers' interesting. First, video on a small screen does not require the bandwidth of full-screen TV.

Second, solid-state memory cards are getting cheaper and more capacious, enabling mobiles to support the kind of caching and time-shifting that is emerging on the home systems being developed.

As PCW reported last month, Compact Flash cards can now hold 4GB, which is almost as much as a DVD disk. Smaller capacities are quite affordable.

Finally, Dab is designed for mobile use. One of its aims was to avoid the fading caused by interference between multiple signal reflections in built-up areas. Dab processes these reflections so as to reinforce the signal.

According to Simon Mason, head of product development at NTL Broadcast, Dab TV image quality using the latest compression techniques is "not so hot for sport [because fast changing images don't compress so well] but fine for talking heads".

NTL is not about to start a mini-TV station, but is simply looking at ways to exploit the possibilities of Dab. One is location-based services.

Mason envisages that you could use a standard web link, via Wi-Fi or a docking station, to download basic data for an area you are visiting.

When you reach the area, the local Dab station could "trickle charge your device with low-latency information".

This means weather and traffic updates, hotel availability and information on events which would be sent repeatedly with the station's audio data stream.

Clearly, this could be financed by sponsorship and adverts. The system could also be used for selling all kinds of digital content. A record company could broadcast its top 10 records, and charge you an unlock fee for a permanent copy.

This is a more efficient and neighbourly way to distribute music than P2P, and if providers don't get too greedy it could kill off a lot of piracy.

Microsoft stands to make a lot of money if this system takes off because NTL is using its media player and digital rights system. Mobile phone operators could gain revenues by providing a back channel for responses and purchases.

"I am absolutely confident of the technology," said Mason. "But we can only take it forward with partners. We need to partner with four or five big content providers."

Perhaps the most significant aspect of all this is that it shows the mobile computer developing as a medium in its own right, a love child of broadcasting and the web. TV is a 6ft medium: you sit that far away from it, which is good for images but not text.

A Dab mobile is a 2ft medium, good for both images and text. The images may be smaller, but they are closer. It can be TV, radio, audio player, video player, book, phone or web page - or it can be all of them at once.

Who knows what is going to be done with it when people discover its potential?

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