Hams cram bands with TV Pi in the sky

It's TV, Jim, but not as we know it

The UK government may be used to flogging off frequencies for billions to mobile operators, but one lucky bunch of radioheads have just seen all their Christmases come at once. Regulator Ofcom has lent three new slices of etheric playground to British radio hams, with strict instructions to be awesome on there. The new bands at 70.5, 146 MHz and 2.3 GHz aren't to be used for idle chit-chat about dipoles or doom (Private Frazer would be drummed off certain frequencies for his incurable optimism) , but to develop new data standards and experiment with digital voice and video.

To get radiating you have to be a licensed ham and ask for access rights, and Ofcom warns that it may take the bands back if there are problems or someone else fancies them. Still, tests are already under way with digital TV that uses a fraction of the bandwidth of the stuff you get from Aunty. In a special edition of the British Amateur Television Club newsletter, BATC reports that using a combination of Raspberry Pis and open hardware and software, full-motion colour TV has been reliably sent and received over hundreds of kilometres using less than one-tenth of the airwaves needed for a channel of old-style analogue telly. Called RB-TV - reduced bandwidth television - it's based on existing DTV standards, but with much lower symbol rates, a job that's not as simple as just picking a lower sample rate for your MP3 compression.

While hams worldwide have dozens of bands available to them, from longwave to microwaves, most are either too crowded or too small for TV or broadband data. Those with room are all UHF and above, which is intrinsically short-range - although there are a few terrestrial repeating stations for TV. The new bands at 70.5 and 146 MHz have the potential for longer ranges, and there's talk of getting the new low-bandwidth TV stuff onto lower frequencies still.

The new bands have come about because existing commercial and government users have migrated to new digital systems (with varying amounts of competence) elsewhere on the spectrum - people like the gas board, the AA and the plod - although north of the border there are still some legacy users which mean the Scots can't get at the 70.5 MHz chunk just yet. Also, some bits of the coast near Ireland and France can't play with 146 MHz for fear of upsetting the less well-endowed neighbours.

With the great British public now thoroughly saturated with UHF digital TV and broadband wireless data, there's no obvious commercial use for the old frequencies. Below about 150 MHz, antennas are too big and propagation too variable to make them palatable. Indeed, large chunks of the VHF spectrum between 30 and 60 MHz haven't been reallocated since the BBC closed down 405 line telly in 1985, and with nobody lining up to claim the FM analogue broadcast band it's looking like analogue switch-off there can be delayed indefinitely.

So, the hams get to play - and get to develop new ideas that, although they too have no obvious commercial benefit, may still end up being useful outside the hobby. And if not, it'll still be damn good geeky fun.