Earlier last month, television in America underwent its biggest change in more than 60 years. The last of the big television stations still broadcasting in analog turned off their transmitters and begin digital transmissions only. Half of the country's 1,700 or so television stations that transmit their signals at full power have already ceased sending out analog signals. But those were almost entirely in rural areas. For the majority of those Americans who get their television free over the air, this was a big switch-off.

The 12 million American households with television sets that use rooftop or rabbit-ear aerials to pluck television signals from the ether will need a converter box to receive the new all-digital broadcasting. Despite a four-month postponement sanctioned by Congress, a USD 2 billion national publicity campaign and free USD 40 coupons to help pay for converter boxes, more than 2 million television sets will go blank.

Fortunately, most Americans pay for television service from a cable, satellite or telephone company. These 114 million households will not be affected. Such services have been digital for years. Their set-top boxes do all the necessary conversion to allow older analog sets, as well as newer digital ones, to receive digital broadcasting.

America is not the first country to cease broadcasting analog television, but it is the largest so far. Germany and a handful of smaller European countries have already done so. Japan and Canada plan to make the transition in 2011, Britain in 2012 and China by 2015. They are all making the move for the same reason. Because digital transmission uses airwaves far more efficiently, switching off bandwidth-hogging analog television frees up broadcasting spectrum. This can then be auctioned off to deep-pocketed mobile-phone companies.

Last year, the American government raised USD 20 billion from auctioning'mainly to Verizon and AT&T, the country's two biggest mobile carriers'swathes of the 700 MHz band used by television channels 52 to 69 alone. These frequencies, along with other UHF and VHF parts of the spectrum used by analog television, are now to be vacated.

The mobile-phone companies have lusted after the 700 MHz frequencies in particular. As television broadcasters have amply demonstrated, such signals can be beamed for miles, suffer little atmospheric absorption, go through brick walls and penetrate all the nooks and crannies inside buildings. So they are ideal for mobile-phone or broadband service.

Governments are not the only fans of digital television, broadcasters have welcomed it, too. It allows them to deliver either a large number of new channels with a picture quality no better than today's television, or a few new channels with the superior video quality of high-definition television. What is rarely mentioned is that going digital will also let television broadcasters break into the telephone and internet-access business, as their cable-television rivals have already done.

So, what is in it for the consumer? Pin-sharp pictures and pristine sound? Not necessarily. But video and audio quality can be improved if broadcasters take pains, and are not too greedy in the way they cram channels into their allotted digital spectrum. Done correctly, digital broadcasting can make images sharper on even the oldest of analog sets'with none of the "ghosting" and other electronic noise that marred analog broadcasting.

The real attraction of digital television, however, is the on-screen program guide. With a menu of options listed on the screen by time and channel, program selection becomes a doodle. Some converter boxes let you use the on-screen guide to choose which program to record. People with cable or satellite television take such digital features for granted. But they are new for over-the-air television.

Getting the best out of all-digital broadcasting will probably mean replacing, or at least repositioning, the indoor or rooftop aerial. That takes patience, trial and error, with small adjustments to the aerial's orientation being made as you switch from one station to another. Think about buying an aerial with a built-in signal amplifier, especially if the television set is more than 20 feet (six meters) away. The longer the coaxial cable has to run, the weaker the signal. However, do not be pressured into buying a special ‘digital' or HDTV aerial. Any aerial that can pick up UHF and VHF signals will receive digital television signals.

If you are lucky, your local television stations will all have their transmission towers in the same part of town and the aerial can then be pointed in one general direction. But if you used to tune to television stations in towns in opposite directions, you may have to choose which ones you want most. Alternatively, you can try an omni-directional aerial to see if it can pull in signals from both directions without causing too much pixelation. Pixelation occurs when the digital signal bounces off buildings, hillsides, trees or even passing aircraft.

The good news is that smart aerials, which automatically aim themselves at stations selected with the on-screen guide, can be had for little more than USD 100. The bad news is that not many converter boxes work with them.

After reading a review of over three dozen converter boxes by consumer reports, your correspondent picked a Spica AT 2018 for one of his superannuated television sets. Apart from scoring highly for picture quality and program guide, the Spica was one of the few with both a connection for a smart aerial and a pass-through for analog signals. The pass-through feature lets you tune into the low-power television stations and rural relay stations that will continue beaming analog programming.

Finally, do not expect miracles from digital television. If all you got previously was a grainy, but still watchable, picture, you may well get nothing at all from digital versions of the channels or, at best, a picture that frequently freezes or pixelates. Unlike analog signals, which tend to degrade gradually when digital signals drop data, the picture can freeze abruptly.

Also, in the days following the switchover, the digital signals being broadcast are unlikely to be up to snuff. Most television stations will use backup antennas during the transition while their old analog ones are taken down from their towers and replaced with new digital masts.

So, for the first week or two after the switchover, use the converter box's on-screen menu periodically to scan for new digital stations. Some that may have been too weak for you to receive initially may come through loud and clear once they are broadcasting at full power.

But do not expect to carry on watching television like this for another sixtys years. Long before our present television sets give up the ghost, many of today's broadcasters will be dead and buried and most of us will be receiving our television pictures direct from the internet.

Courtesy- The Economist Newspaper Limited 2009