April 4 will see the start of the biggest event in Britain’s five-year mission to convert terrestrial TV from four or five analogue channels to 30 digital channels.
Over two weeks, the Crystal Palace transmitter in London and its 52 relays will switch off analogue TV as Freeview takes over the airwaves.
The London digital switchover will affect 4.9 million homes – 18 per cent of the UK population – many of whom will be able to get Freeview for the first time.
That’s because 49 of London’s relays – covering areas such as Woolwich and Hertford – will be beaming out Freeview signals for the first time, and Crystal Palace’s Freeview output will become 10 times more powerful.
Since 2007, 11 of the UK’s 15 TV regions have already switched off analogue TV, with just London on April 18 and Meridian East (Dover) on June 27 to go before the Olympics in July.
After the summer, Tyne Tees will switch on September 26, and Northern Ireland will complete the programme on October 24.
The £630m programme will give 98.5 per cent coverage – the same as analogue TV – for the 15 ‘public service’ Freeview channels, including high-definition versions of BBC One, BBC HD, ITV1 and Channel 4 (with another channel expected later this year LINK).
The full Freeview service of 30 channels will be available to 90 per cent of the UK’s population, all from more than a 1,100 main and relay transmitters which have been upgraded since 2007.
The hard work in this scheme has been done by Arqiva, which owns and operates the UK’s TV and radio transmitters on behalf of the BBC and commercial broadcasters.
Recombu Digital was given a rare chance to visit the Crystal Palace transmitter site and see how it’s been changed ahead of transmission.
The UK has 80 main TV transmitters, all of which have replaced a room like this with a digital transmitter room.
This entire room holds four analogue TV transmitters for BBC One and BBC Two, which pump out a Megawatt (1,000,000W) for each channel.
There are four amplifiers so that there’s a backup for emergencies and repairs, although there are also backups at other nearby sites in case of a fire to keep the antennas on top of the mast beaming out signals.
These amplifiers have been operational since colour TV began in the 1960s, although the old klystron amplifiers have since been replaced by more efficient Induction Output Tubes.
Nevertheless, it’s still an incredibly noisy place, mostly thanks to the water cooling and air-conditioning needed to keep it from overheating.
ITV1, Channel 4 and Channel 5 all have smaller, slightly less impressive rooms hosting their amplifiers.
On April 8, this room will host the first part of Britain’s digital switchover, when the BBC Two signal is switched off so that the main BBC Freeview multiplex (a collection of TV channels) is turned up to full power.
Even then, the BBC Two equipment will have a short extra life amplifying ITV1’s analogue signal for the final two weeks so the ITV amplifiers can be decommissioned.
Andrew Elston, Arqiva’s Digital Switchover manager, explains the racks of transmission equipment in terms Recombu Digital can understand.
In short, it mixes the digital TV signals received by fibre-optic cables from the BBC TV Centre in West London and converts it to an analogue signal.
The digital audio is also converted to NICAM stereo and then mixed in with the TV signal before it’s boosted to UHF TV frequencies and delivered to the transmitters to be amplified and sent to the antennas.
The analogue TV was there for our benefit we suspect, and the monitoring equipment here is for on-site troubleshooting rather than constant attention – Arqiva has a national monitoring centre in Yorkshire for all of its transmitter sites.
One function that doesn’t happen in London is amplifying Teletext and Ceefax signals – they don’t degrade over the short distance from central London as they do to the other main transmitters.
Million-Watt TV signals would burn through a typical TV antenna cable like matchwood, so they’re routed through coaxial waveguides – effectively giant pipes for TV.
This room is where ITV1’s analogue signals from the two transmitters are mixed and switched – manually – to keep the channel on air.
There’s huge amounts of energy passing through the waveguides, so like the transmitters, it’s all water-cooled and air-conditioned.
All of the analogue transmission equipment, here and across the UK, will be decommissioned and dismantled by Arqiva after Digital Switchover.
It won’t be dismantled, though – everything will be recycled if possible. The transmitters are still very valuable in themselves, there are thousands of useful components, and tons of valuable copper and other metals.
Arqiva’s Digital Switchover manager Andrew Elston will really be doing this on April 18 – turning off the transmitters for Channel 4’s analogue TV signal.
He won’t be the only one making manual changes, since the 52 London relays from Guildford to Reigate will also need teams present to make sure the switch has gone smoothly.
The switchover was even more complex for south Wales in 2010, when 83 relays had to be activated by 25 very busy engineering teams.
New technology has made Arqiva’s job easier since the start of the switchover programme, and contributed to a major underspend on the original estimate of the cost of Digital Switchover.
Among the innovations have been relay transmitters which can handle both analogue and digital TV signals, and will automatically switch to the digital signal when they detect it, so there’s no need for an engineer to be present.
The digital transmitter room handles all six Freeview multiplexes (groups of channels) in the same space occupied by the BBC’s analogue transmitters.
It’s all the more impressive because there’s a back-up transmitter for each multiplex, and the whole place is a good deal quieter than the analogue TV transmitter rooms.
Another similarly-sized room next door hosts the waveguides and other equipment for the three antennas on the mast above: one for the three public service multiplexes, another for the three commercial multiplexes, and a third back-up which can host all six multiplexes in an emergency.
The third antenna is still being fitted to the mast – it’s not essential for Digital Switchover to go ahead.
The Crystal Palace amplifiers have been running for several months so that they could be fully tested before the big day.
One reason the digital transmitters are so much less noisy than the analogue is that even at full power they’re just one-fifth the strength of analogue TV.
The current power or Freeview from Crystal Palace is 20kW, and at the end of switchover on April 18 it will be boosted to 200kW.
It’s the same across the UK, so Digital Switchover will save a huge amount on the energy bill for transmitting UK TV channels.
The thousand-plus relay transmitters are a lot simpler than this – most of them use solid-state amplifiers which are a lot cheaper, more efficient and more reliable than the huge tube transmitters.
At the base of the transmitter mast, huge conduits carry the TV signals to the antennas 219m above.
These are analogue TV signals: having been tested, the digital signal conduits were being buried in culverts as we visited, and the workmen didn’t want to be photographed.
The mast’s other corners include a lift which climbs slowly to a platform at 130m. Very slowly, 30 minutes in fact, and then there’s a 40-minute climb to the TV antennas at the top.
For the Digital Switchover work, Arqiva installed a cable-car to the top which climbs in just seven minutes.
The view’s magnificent, but as Andrew Elston points out: “It seems the weather’s never nice when you have to go up there!”
Climbing up the final corner are connections for mobile phone, DAB digital radio and analogue radio antennas which share the mast – as they do at most others.
Peter Heslop, Digital Switchover programme director for Arqiva, says that coordinating with these other users has been a key part of the programme’s success.
Not only is there a lot of live electrical kit around, high power radio waves are pretty harmful as they come out of the antennas, so everything had to be turned down or switched off so Arqiva’s engineers didn’t slowly cook while they worked.
The Digital Switchover programme will take a break this summer so that there are no disruptions during the Olympic and Paralympic games.
There won’t be a break for Arqiva’s engineers, though, who rely on good summer weather to work on transmitter masts and still have essential work to finish for Tyne Tees and Northern Ireland.
The Digital Switchover programme saw four of the UK’s main transmitter masts replaced with new structures: Black Hill in Scotland, Caldbeck on the Scottish Borders, Divis in Wales, Rowridge on the Isle of Wight and Tacolneston in Norfolk.
The summers of 2007 to 2009 were some of the wettest on record, and threatened to put the entire programme behind schedule.
Fortunately, Arqiva was able to import a helicopter crew who were able to drop entire pre-constructed transmitters on top of a mast, instead of winching them up piece by piece.
The technique was new to the UK, but reduced weeks of work to a single day and put the programme back on track with the help of two dry years.
Peter Heslop, Digital Switchover programme director for Arqiva, revealed that they also received unexpected delays from wildlife such as ground-nesting grasshopper warblers and merlin birds-of-prey.
The latter are so endangered that Arqiva’s engineers couldn’t even be told the exact nesting sites in case collectors were tipped off and stole the eggs.
At Belmont, the UK’s tallest broadcasting mast – some locals were annoyed that Arqiva wanted to reduce its height, and made a last-minute bid to get the mast listed by English Heritage. “Good sense prevailed and we were able to go ahead,” says Heslop.
More seriously, fire broke out when a new transmitter was switched on for Oxfordshire – covering the constituencies of both prime minister David Cameron and culture secretary Ed Vaizey. The mast had to be completely rebuilt.
On April 18, Arqiva will mark the London digital switchover by turning Crystal Palace’s TV mast into a lightshow to rival the Eiffel Tower for two nights. Let’s hope the weather’s good.