The Independent Broadcasting Authority built the Preseli transmitting station in 1962 to bring commercial television to west Wales. The mast is a guyed steel lattice structure 235.4 metres tall, anchored at 1,835 feet above sea level on a hilltop near the villages of Crymych and Pentre Galar. Transmissions began on 14 September 1962 using the old British 405-line VHF standard on Band III channel 8. A triangular array of antennas aimed three beams of signal: one toward Pembrokeshire, another toward western Carmarthenshire, and a third northward that covered south-western Cardiganshire and also fed a relay transmitter at Arfon in north Wales. The programming was Welsh-region ITV, initially provided by a short-lived company called Teledu Cymru, taken over by TWW in 1964 and eventually by HTV Wales from 1968. Colour television did not arrive in west Wales until 1973, when the site was upgraded to transmit 625-line UHF PAL signals - late by UK standards, and not even the area's MP could get it started any quicker.

By 1971, Welsh-language activism had been pressing for a dedicated television channel for years. Cymdeithas yr Iaith Gymraeg, the Welsh Language Society, had pursued direct action since its founding in 1962, including the painting-out of English-only road signs and the disruption of court proceedings. The Preseli mast climb was part of that campaign. Three protesters gained access to the site compound, scaled the lower section of the lattice, and refused to come down. They were charged with conspiring to trespass and sent to prison. The mast they climbed had been built to carry English programmes into Welsh homes. They wanted Welsh-language programmes carried with the same reach. The campaign succeeded eleven years later when S4C launched in November 1982, broadcasting on the same Preseli mast that the activists had climbed. The protests are now a footnote in Welsh broadcasting history. The channel they fought for is still on the air.

The Preseli mast was designed to cover west Wales. What its planners did not fully anticipate was that the signal would carry across the Irish Sea. From 1962 onward, households along the east and southeast coast of the Republic of Ireland - mainly in counties Dublin and Wicklow - found that pointing outdoor aerials westward toward the sea picked up Welsh television. Welsh BBC and Welsh ITV programmes became part of the everyday viewing diet of Irish households who could not officially receive them. When cable television launched in Ireland in the early 1970s, the cable operators carried these Welsh stations as a recognised service, since they were already the main signals available in Dublin and Wicklow. For four decades, Welsh rugby, Welsh news, and Welsh light entertainment reached Irish living rooms by accident - a small unintended export of culture across one of the world's busiest sea lanes.

The VHF 405-line transmissions ended in January 1985 after 22 years and three months of service. Channel 5 launched as an analogue UHF service in 1997 on out-of-band channel 37, an unusual configuration forced by the fact that British UHF television planners had never expected a fifth channel. Six digital multiplexes were added in November 1998 using the DVB-T standard. The QAM constellations and carrier counts were reconfigured around 2002 after the collapse of ITV Digital, when Freeview took over the digital terrestrial service. Analogue television finally shut down at Preseli on 19 August 2009 for BBC2 Wales, with the rest following by 16 September. The transmitter site was reconfigured to deliver six digital multiplexes at full power. In 2012 the 4G mobile clearance of the 800 MHz band forced a frequency reshuffle - the Arqiva B multiplex moved from channel 49 to channel 39, BBC B from channel 50 to channel 40 - and the configuration has remained broadly stable since.

Today the Preseli transmitter is operated by Arqiva. It carries Classic FM on 100.5 MHz, Heart South Wales on 105.7 MHz, and since 2017 Nation Radio on 107.10 MHz, broadcasting at 2.5 kilowatts on a directional antenna that pushes the signal across all of Pembrokeshire and most of Carmarthenshire. National DAB multiplexes for the BBC and Digital One run from the same mast. The six digital television multiplexes carry the full Freeview service to most of west Wales. From the air the structure is unmistakable: a thin red and white needle 235 metres tall, rising from a hilltop on the eastern Preselis where Foel Cwmcerwyn falls away toward Crymych. Standing under it, the guy cables stretch out across the moorland in three directions like a vast tent. The mast hums in high wind. From the top - if you ever made it to the top - you could see Snowdonia to the north and the Bristol Channel to the south. Most days it just stands there, silently sending Welsh television to anyone who tunes in.