The Masts and Towers of Broadcasting
In January and May this year I visited the transmitter mast at Holme Moss, the site that serves our area and most of the north of England with FM and DAB radio. It stands on a summit 524m above sea level and is itself 228m high, broadcasting the national channels with 250kW. It was originally built to transmit the single BBC TV channel from 1951, which it did until the black-and-white 405 line service ended in 1985, at which point the old mast was demolished, a new one already in service on the same site. In 1956 it also became a radio site, transmitting VHF (FM) when that service first began. My feet got wet on the peaty moorland. Construction of the 140 ton lattice steel mast cannot have been easy.
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From the high ground that the mast is built on, I could see two other transmitting stations: the twin masts of the powerful (200KW) medium wave transmitter at Moorside Edge, and, ten miles away across the moorland, the huge concrete tower of Emley Moor, flanked by a mast of similar height, which broadcasts TV to a large area east of the Pennines. Holme Moss, however, carries radio for both sides of the country.
Here in the west, our TV comes from Winter Hill, north-west of Bolton, standing 778m above sea level. The mast is 309m tall, making it the highest TV transmitter in the UK. As VHF and UHF radio waves are line-of-sight, height is necessary to reach a wide area. Its tubular construction is the same as the ill-fated 386m mast at Emley Moor, which collapsed in 1969 during bad weather. I remember the incident well, at the time living in the East Riding (N. Humberside). Despite our area's signal coming from Belmont, south of the Humber in Lincolnshire, it felt local, Look North showing pictures of the devastation and reporting the gradual restoration of service. BBC2 was rebroadcast from Emley, so we lost it for a few days until an alternative feed route¹ was set up. Although a build-up of ice on the wire stays was blamed initially, an inquiry concluded that a strong, steady wind caused the tall tubular structure to resonate at a low frequency, and the oscillations increased until they destroyed the mast. Fortunately, although it fell onto parts of the transmitter buildings, the local Methodist chapel and across a road, no-one was hurt.
Following the collapse, heavy chains to damp oscillations were hung inside the remaining five masts of similar design. Winter Hill, for instance, had 152 tons of chains added. The steel tube, supported by stays, provides protection from the weather for engineers ascending it (the lift inside Emley Moor takes 7 minutes to reach 274m). They are, after all, not only amongst the tallest structures in Europe but also in some of the most exposed areas of the country. However, it was decided to replace Emley Moor with a concrete tower, which became the UK’s tallest self-supporting structure at 330m. As I photographed it across the hills, there is a lattice mast alongside, nearly as tall as the tower, which was built in 2018 to take over transmissions while the tower was shortened and given new antennas for the 700MHz clearance. It was a major construction project in its own right, taking over a year from the first ground works, and with lengthy delays waiting for weather calm enough for the highest sections to be added using a helicopter. Yet it is only temporary. It has already been auctioned off and will be dismantled. I can’t tell you what it cost to erect, but the government put in £500M to retune the entire country to make way for more mobile phone services, and temporary masts like this were used at several major sites to ensure quality of reception during the process.
Just last year (10 August 2021) we lost another main transmitter at Bilsdale in N. Yorkshire, depriving some 670,000 households of TV and FM radio. Water got into electrics, and smoke was found billowing out of the tubular mast like a chimney, which had to be demolished as it was unsafe. Also taken off-air were its 15 relays that provided local fill-in where high ground masked the signal. Following the fire in August, an 80m temporary mast was erected nearby in September, and many relays were upgraded and provided with a feed from elsewhere (either another main transmitter if possible or satellite) so they could reach more viewers, and some new sites added. Unlike in 1969, there are now alternatives in the shape of satellite (Freesat and Sky) and the Internet, and vouchers were provided to people in areas still wholly without signal to obtain streaming sticks. A new 303m mast, this time of lattice steel construction costing £30M, is being built.
Fortunately no-one was hurt in either incident, but working on these structures remains dangerous and very subject to weather conditions. In 1982, a 1971ft (600m) mast in Missouri City, Texas, was nearing completion. The second of an array of FM antennas weighing 6 tons was being craned into place when a U-bolt securing it failed. The array crashed to the ground, severing one of the guy wires on the way. The sudden release of all the tension in the wire (more than 9 tons force) caused the mast to sway and then buckle, and in a few seconds it was a crumpled heap on the ground. All five men working on the mast died.
So next time you turn on the TV, spare a thought for the brave people who build and maintain the infrastructure that makes it possible.
See more pictures in the Holme Moss Gallery
[1] Interestingly, the new feed was obtained from Waltham to the south (which, like Emley Moor and Belmont, was also a tubular mast and had suffered a collapse during construction in 1966, though for different reasons). Quite understandably, no-one wanted to work on the mast until the cause of the Emley collapse had been determined and the ice had gone, so the engineers set up a mobile tower and transmitter truck at the end of the driveway to the north, so it was exactly between Belmont and Emley. They pointed one antenna at Waltham to receive the signal and retransmitted it on Emley’s frequency through another antenna pointing into Belmont’s receive antenna. Quality may have suffered a little, but service was restored safely!
The technique was not exactly a new idea. In the days when the services shut down at night, relays, which were unattended, shut down on a timer after the main transmitter closed down, but they always did so some 45 minutes after the scheduled time in case programmes overran. Cheeky teenagers would sometimes take advantage of that brief opportunity late at night by pointing a low-powered transmitter into the relay’s receive antenna and playing a tape they had prepared earlier, thus getting their programme broadcast to the entire area.
These days, large sites have cable feeds and many have satellite feeds as backup too.
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