Anthorn VLF transmitter

Anthorn radio station is located near Anthorn, Cumbria, England and is operated by Babcock International ( with whom former operators VT Communications are now merged ). It has two transmitters: one VLF and one LF.

The characteristic triangular pattern of roads is a remnant from the World War II military airfield which was operated by the Royal Navy Air Service as HMS Nuthatch.

VLF transmitter

The VLF transmitter is used primarily for transmitting orders to submarines on 19.6 kHz. Its callsign is GBZ.

It is a NATO facility, controlled from Northwood Headquarters along with three other VLF transmitters in Norway, Germany and Italy. In accordance with the procedure for NATO projects, the project was the subject of a competition among the organisation's member countries. The British Post Office, acting as technical adviser and agent of the Ministry of Defence, chose the site, negotiated the contract and supervised the work, with the assistance of the Ministry of Public Works and Buildings. The contract was placed on 26 October 1961 with Continental Electronics Systems Incorporated of Dallas, Texas. This firm had already built a similar but much larger station in Maine, USA. Work began in 1962 and the station was accepted on behalf of the MoD in November 1964.

Originally, the station was designed to radiate a single telegraph channel at up to 45.5 baud and at powers ranging from 50 kW at 16 kHz to 100 kW at 20 kHz. The carrier frequency was to be stable to one part in 108 over a month. Subsequently the data rate was increased to 50 baud and the carrier stability improved.

LF transmitter: National Physical Laboratory time signal

The National Physical Laboratory (NPL) has installed three atomic clocks at Anthorn and on 27 February 2007 Britain’s national time signal transmissions, retaining their original call sign of MSF, were transferred there on a trial basis, moving formally on 1 April 2007. Monitoring and logging of the clocks and control of the transmissions is by internet link from the NPL offices at Teddington, using comparison with GPS signals at both locations. Signal monitoring is by radio. To ensure accuracy, dynamic adjustment of the aerial according to local conditions (such as wind distortion) is controlled from computers on site. The signals, transmitted at 60 kHz, also provide a national frequency standard. The effective radiated power is 15 kW.

LORAN

The General Lighthouse Authorities for Britain and Ireland have contracted VT Communications to develop eLORAN (enhanced LORAN) radio navigational aid for mariners. The transmitter is at Anthorn.

Antenna System

The antenna system consists of 13 masts, each 227 metres ( 745 ft) tall, which are arranged in two rings around the central mast. The VLF antenna consists of 4 rhombic antennas hung on large insulators on the masts, which are all grounded.

The LF-antenna is a T-antenna spun between two masts.