By Jim Reed
Newsbeat technology reporter
The BBC has started testing a new digital television system that lets you watch shows in sharper, high definition without buying a satellite dish.
The trial in south-east England will let engineers test out a new signal that works through a standard aerial and HD set-top box.
If successful the first full HD transmission could start in 2009.
Four, free high definition channels will be available, including the BBC's own HD service.
An auction will be held for the other three slots with ITV, Channel 4, Five and Welsh network S4C all expected to bid.
Viewers will need a new Freeview HD box and will have to wait until the analogue TV signal is switched off in their area before they can see the channels.
The north-west of England will be the first region to get the broadcasts in 2009. The last areas to switch will be London, the north-east of England and Northern Ireland in 2012.
Just under 10 million homes now have a flat screen TV capable of receiving HD broadcasts but most don't have the receiver or subscription needed to watch television in the new format.
That is starting to change as the cost of high definition equipment begins to come down.
The BBC and ITV recently launched a satellite TV system called Freesat which lets users watch a limited number of HD channels for a one-off fee of around £200.
Cable company Virgin Media offers a digital video recorder called V+ "for free" but charges a £150 installation fee.
The only live high definition channel on the platform is BBC HD but it also comes with 2,000 hours of video-on-demand programming, some of it in high definition.
Sky HD price cut
Sky recently said it is cutting the price of its HD set top box from £250 to £150, the same price as its Sky+ standard definition kit.
But subscribers must pay an extra £10 a month to receive up to 14 HD channels depending on their television package.
Earlier this year, the telecoms regulator gave the go-ahead to free HD broadcasts over the terrestrial airwaves.
But each high definition channel will need to display five times more data than a standard television channel.
That restricts the amount of stations that can be squeezed into the free-to-air television spectrum.
A new type of technology called MIMO could increase the number of Freeview HD stations from four in the future, although some users might be forced to upgrade their aerial systems to receive the broadcasts.