Orfordness Transmitter

The Orfordness transmitting station is a major radio broadcasting facility at Orford Ness on the Suffolk coast in the UK. It is designed to transmit powerful medium-wave signals to much of Europe on two frequencies (648 and 1296 kHz). Built in the 1970s and early 1980s by the British government, it is now owned by a large engineering and defence services company, the Babcock International Group.

Over the years, the Orfordness station has carried a variety of radio services. It is best known, particularly in the UK, for transmitting the BBC World Service in English around the clock on 648 kHz from September 1982 until March 2011. Following the ending of these broadcasts, and with no other major clients for the station, its future is uncertain.

The station's name is written as one word while the shingle spit on which it sits is two words.

History

The site was originally built for an experimental over-the-horizon radar station known as Cobra Mist.

The radar never worked satisfactorily and the project was scrapped in 1973. The site and buildings were taken over in 1975 by the Foreign and Commonwealth Office's Communications Engineering Department (still better known by its previous name, the Diplomatic Wireless Service), who installed a 50-kW medium-wave broadcast transmitter. Following successful tests and installation of further transmitters, from 1978 the site gradually took over responsibility for the BBC's medium-wave services to Europe which had been provided since the Second World War by an FCO transmitting station at Crowborough in Sussex. From September 1982, Orfordness handled all such BBC transmissions. In 1986, the BBC itself took over the running of the site from the FCO, although the latter retained ownership of the station.

In 1997, as part of the privatization of all transmitting stations in the UK used by the BBC, the station was bought by Merlin Communications International Ltd (usually known simply as Merlin), a company formed by former BBC engineers and frequency managers. In 2001, Merlin was acquired by VT Group plc (known as Vosper Thorneycroft until 2002) and renamed VT Merlin Communications, then just VT Communications. In 2010, VT Communications was bought by Babcock.

Current broadcasts and future plans

As part of changes caused by a cut in the BBC World Service budget, transmissions in English on 648 kHz AM from Orfordness ceased on 27 March 2011.

The 648 channel remained silent until 4 August 2011, when the Dutch domestic news/information network Radio 1 began temporary broadcasts from Orfordness as an emergency measure following fires at the Lopik and Hoogersmilde FM transmitting sites in the Netherlands on 15 July 2011.

Orfordness still broadcasts BBC World Service for two hours a day on 1296 kHz using the DRM digital radio system. A further two hours a day (Monday to Friday) on 1296 are hired by Radio Netherlands to broadcast in Dutch on conventional analogue AM to the Benelux countries.

In August 2011, the station's owners, Babcock, informed the BECTU trade union that four job posts at Orfordness were "at risk of closure", following the cut in the BBC World Service's use of the transmitters.

Transmitters

A number of transmitters have been installed on the site over the years, the most powerful being an AEG-Telefunken S4006 which has a maximum output of 600 kW. However, registration listings for both 648 and 1296 kHz have always given 500 kW as the maximum power used on both frequencies.

Transmissions on 648 kHz from the AEG-Telefunken S4006 use dynamic carrier control, an energy-saving technique in which the power of the transmitter's carrier signal is reduced when the audio level is low.

Other transmitters include two Doherty 250 kW units, designated ORF 2A and 2B (both originally at Crowborough), whose outputs can be combined to give 500 kW on a single frequency.

The newest transmitter is a 200 kW NA200 from Nautel of Canada. The NA200 (designated ORF 4) was commissioned in 2003 prior to the World Radiocommunications Conference (WRC) in Geneva, Switzerland, and was on the air for the inaugural DRM broadcasts.

Aerial systems

The station has two directional aerial systems: one for 648 kHz and one for 1296 kHz.

The directional aerial for 648 kHz (erected in 1981-82) consists of a row of five 106.7 metre (350 ft) freestanding steel lattice towers of triangular cross section, insulated at their base. All five towers are driven. It is beamed at 131 degrees (i.e. south-east) though for practical purposes the exact bearing is nominal as the beam is very broad towards the east and south. It provides daytime coverage of Belgium, the Netherlands, Luxembourg, north-east France and north-west Germany by ground wave propagation; and night-time coverage of much of Europe by skywave propagation.

The directional aerial for 1296 kHz (erected in 1978) consists of six freestanding steel lattice towers. Unlike the directional aerial for 648 kHz, they are arranged in two parallel rows with three towers in each. Only the middle tower of each three is driven: the other towers act as passive reflector and director elements. It is beamed at 96 degrees (i.e. east) and was originally mainly intended for night-time (skywave) coverage of Poland, Czechoslovakia, Hungary and the western USSR, key target areas for the BBC during the Cold War. It can also be used for daytime coverage of the Benelux countries.

Both the 648 and 1296 directional aerials have limited radiation to the west, meaning that, despite the high power of the transmitters, reception of Orfordness within the UK is poor or non-existent, with the notable exception of parts of south-east England and East Anglia.

There is also a back-up omni-directional mast radiator for 648 kHz (erected in 1983), which can only handle transmitter powers of up to 250 kW. This is only used when maintenance work is carried out on the directional antenna.