The Mendip transmitting station is a broadcasting and telecommunications facility, situated on the summit of Pen Hill, part of the Mendip Hills range in Somerset, England, at 305 metres (1,001 ft) above sea level. The station is located in St Cuthbert Outcivil parish in Mendipdistrict. It includes a 281.6 metres (924 ft) tall mast, which was built in 1967 and weighs around 500 tonnes, and is the tallest structure in the southwestern England. The mast broadcasts digital television, FM analogue radio and DAB digital radio, and had broadcast analogue colour television from 1967 until 2010.
Until 2008 a GRP aerial cylinder, which contains the analogue television transmitting antennas, was located at the top of the mast, bringing the total height of the structure to 305 metres (1,001 ft). With a mean height of 596 metres (1,955 ft) above sea level, the analogue television antennas were amongst the highest in the UK. The analogue television antennas were removed in 2010, the original antenna cylinder being replaced with a new antenna assembly, ready for digital switchover in 2010. The new assembly is slightly shorter than the previous cylinder causing the overall mast height to be reduced from 305 metres (1,001 ft) to 293 metres (961 ft).
There are red aircraft warning lamps (six sets of two lights) up the mast with two lights on top. The lights were upgraded in February 2007 to comply with CAA 2000 Air Navigation Order, designed to prevent low flying aircraft from hitting the mast.
The station is owned and operated by Arqiva (which acquired the National Grid Wireless, previously Crown Castle.)
The mast was repainted during 2007.
The mast has become a Mendip landmark, providing a method of identifying the hills from a distance.
Mendip was set up as a C/D group transmitter when it entered service with analogue PAL transmissions. In July 2007, Ofcom confirmed that it would remain a C/D group transmitter at digital switchover. The mast broadcasts digital television over a large area of the west of England, including Somerset, Wiltshire, North Somerset, Bath and North-East Somerset, Bristol, South Gloucestershire and Southern Gloucestershire. The station also covers the coastal areas of south east Wales, and in the days of analogue TV, many households used it in preference to their more local station, Wenvoe. This is because prior to the digital switchover, Mendip carried Channel 4 and Channel 5, whereas Wenvoe only carried S4C, which broadcast a lot of Welsh language programming. Power on analogue transmissions was 500 kW (erp) on channels 1 to 4 and 126 kW on Channel 5. The latter was transmitted outside of the original C/D grouping of the transmitter but most people in reasonable signal areas could receive it anyway, see aerial gain curves. All six digital multiplexes were transmitted at 10 kW until switchover in 2010 when the power on the "BBC A", "BBC B/HD" and "D3&4" multiplexes was boosted to 100 kW. In 2011, SDN was boosted to 50 kW and in 2012 the remaining two Arqiva multiplexes will be boosted to 50 kW too. Mendip's population coverage is around 1.5 million, although some homes in the immediate vicinity, such as those in Cheddar are unable to receive a signal due to being in the shadow of the Mendip Hills and therefore have to depend on local relays.
Mendip broadcasts FM (analogue VHF) radio for BBC Somerset and the Severn Estuary Regional service Kiss 101. It transmits high power Digital Audio Broadcasting (DAB) signals for Digital One and BBC National DAB multiplexes, as well as a lower power local service to Glastonbury for MXR Severn Estuary. These three multiplexes carry approximately ten digital radio stations each. An additional DAB multiplex, MuxCo Somerset, was awarded a licence in 2008 to broadcast local and national services to Somerset. As of 2010, it is expected that MuxCo Somerset will use the Mendip station, though transmissions have yet to commence.
Digital terrestrial television was first transmitted from the Mendip mast from 15 November 1998 using the frequency gaps between the analogue TV broadcasts. To limit interference to the analogue transmissions, power output on the digital multiplexes was low.
On 24 March 2010 BBC Two was switched off on UHF 64 and ITV1 was switched from UHF 61 for its final weeks of service. Multiplex 1 on UHF 59+ was closed and replaced by BBC A on UHF 61 (which had just been vacated by analogue ITV1). BBC A was transmitted at full power (100 kW) and in 64QAM, 8k carriers mode from the start.
Following the completion of analogue TV shutdown on 7 April 2010, Mendip transmitted all of its higher powered multiplexes at 100 kW. From this date until the second-stage switchover of 28 September 2011 the frequency allocation was:
With the completion of digital switchover at Oxford, all multiplexes could be moved to their final channel allocations with the exception of Arqiva A. SDN increased to half its full power output (50 kW).
On 28 March 2012 Arqiva A moved to its final channel allocation at UHF 56, after the completion of digital switchover at Salisbury. Arqiva A and B and SDN also increased to full power (100 kW) on this date.