The structures that power your television
Almost all of us watch TV or listen to the radio, and many know where our favourite soaps are made, but how many of us know about a vital cog in the system - transmitting stations?
In the age of catch-up TV and super-fast mobile internet, where many of us are turning to watch our TV, they also provide a mobile signal to millions. They can be taller than skyscrapers, older than The Beatles, and some of them look a bit like the Eiffel Tower.
Crystal Palace, London
Nicknamed South London's Eiffel Tower, the Crystal Palace transmitter beams television pictures to 12 million sets across London and the South East.
Ronan O'Gorman has been working on transmitting stations for nearly 30 years and has climbed the 719ft (219m) tower more than 100 times.
He said: "It takes six minutes for an electric lift to take you 130 metres up, the rest you have to climb yourself. So in total it takes about 35 minutes to climb.
"It's an adrenaline rush. Once I climbed it and there was very low cloud, we were above it all in bright sunshine and I could see the shadow of the tower on the cloud beneath us."
The tower, like many others, is not just used to beam TV signals. "All the phone companies are there," Mr O'Gorman said.
It is built on the ruins of the Crystal Palace, the Victorian exhibition centre that burned down in 1936. To preserve the beauty of the site, the buildings that house much of the technical equipment had to be put underground.
"You can't extend the underground buildings obviously, it is very difficult to keep the old technology working as you put in the new stuff," the 50-year-old said.
The Wrekin, Shropshire
Shropshire rambler Peter Carr admits he has "no feelings" about the Wrekin transmitter. That is a far cry from 1975, when the tower was finally built.
The Wrekin Preservation Committee, as historian George Evans recalls, was set up in protest at plans for the tower. "We told each other how dreadful it was and wondered what to do about it," he remembers.
But despite protests the tower was built on the Wrekin, after the BBC had looked at putting it on the nearby Stiperstones ridge.
The transmitter sits on the 1,335ft (407m) high Shropshire landmark called The Wrekin, and beams TV pictures to the majority of the county and part of Staffordshire.
Mr Carr's group walk across the county and it would seem they, and other ramblers he has met across the country, no longer have issues with transmitting towers.
"Open-cast mining, pylons, wind farms and solar farms... but transmitter towers never even feature," said 67-year-old Mr Carr, chairman of the Shropshire Area ramblers.
"They are less intrusive than wind turbines."
Sutton Coldfield, Birmingham
Opened in 1949, the longest serving television transmission facility in the UK sits in north Sutton Coldfield.
Beaming pictures to Birmingham and about seven million people across the West Midlands, it is the second most important tower in the country in terms of viewers served.
"If you think of the small coaxial cable that you plug into the back of your TV," said senior engineer Martin Byrd, "the ones that connect into our transmitters are the size of your leg."
The technology behind the towers has got smaller in the 65 years since the facility Mr Byrd oversees opened. But, with the addition of more and more TV and radio channels and high definition, there is still plenty of kit to look after.
Although it is one of the tallest structures in the area, it is not used by the phone companies. Surprisingly they use a second, smaller mast nearby.
Arqiva, the company that manages the TV transmitter, admitted there was "debate" over whether it was the longest continuously transmitting site in the world.
The history of the company, formed from many others, has made it difficult to say definitively whether or not it could claim that title.
Emley Moor, West Yorkshire
The transmitter at Emley Moor stands overlooking the Pennines and West Yorkshire. For people from those parts, catching a glimpse of it on a long journey lets them know they are nearly home.
"Everyone has a view of the mast. On the M1 I see it, on the train I see it; intrinsically it's something to do with coming home," Chris Marsden, of the Huddersfield Civic Society explained.
Built in 1971, the 1,083ft (330m) Grade II listed concrete tower is the tallest self-supporting structure in the UK. It is taller than any of the skyscrapers in London, including The Shard.
Given its extraordinary height, the transmitter also makes a perfect site for the mobile phone companies to use it to provide the area with signal.
But despite its height, the tower has not imposed on locals, according to Kirkheaton resident Sandra Harling.
"It was lit up for the Tour de France and it was absolutely fantastic," she said.
"We've got used to it, and besides it looks much better than the first one."
The Emley Moor site has housed three transmitting towers since it opened in 1956, the second of which collapsed in strong winds on 19 March 1969.
Large amounts of ice stuck to the guy rope that held the 1,256ft (385m) mast up, causing it to come crashing down under the extra weight.
The mast crashed through the roof of the Emley Moor Methodist Church, The Huddersfield Daily Examiner reported, but two men inside were unharmed.
Granville Clay, 79, remembers trying to visit the site of destruction and said: "I couldn't get anywhere near the site, the road was blocked off because the mast landed in it.
"It was quite remarkable there were no injuries."