Transmitter station in the context of Callsign

In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique identifier for a transmitter station. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity.

The use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two-letter identifiers were adopted for this purpose. This pattern continued in radiotelegraph operation; radio companies initially assigned two-letter identifiers to coastal stations and stations on board ships at sea. These were not globally unique, so a one-letter company identifier (for instance, 'M' and two letters as a Marconi station) was later added. By 1912, the need to quickly identify stations operated by multiple companies in multiple nations required an international standard; an ITU prefix would be used to identify a country, and the rest of the call sign an individual station in that country.

Slieve Gallion (Irish: Sliabh gCallann) is a mountain in County Londonderry, Northern Ireland. It is the easternmost of the Sperrin Mountains. It reaches a height of 528 metres (1,732 ft) and dominates the western shore of Lough Neagh. Its prominent northeastern summit has a transmitter station with a small road leading to it, and stands at a height of 496 metres (1,627 ft).

By road, Slieve Gallion is 4 miles (6.4 km) from Moneymore, 8 miles (13 km) from Cookstown, and 8 miles (13 km) from Magherafelt. The mountain is part of the parishes of Desertmartin, Lissan and Ballinascreen.

Slieve Croob (from Irish Sliabh Crúibe 'mountain of the hoof') is a mountain with a height of 534 metres (1,752 ft) in the middle of County Down, Northern Ireland. It is the heart of a mountainous area, the Dromara Hills, north of the Mourne Mountains. It is designated an Area of Outstanding Natural Beauty and is the source of the River Lagan. There is a small road to the summit, where there is an ancient burial cairn and several transmitter stations with radio masts. It has wide views over all of County Down and further afield. The Dromara Hills also includes Slievenisky, Cratlieve, Slievegarran and Slievenaboley.

Slieve Croob may have been the mountain named Brí Erigi or Brí Airige in medieval writings. The cairn on its summit is believed to be the remains of an ancient burial mound, possibly of a passage tomb like the one on Slieve Gullion. In the 19th century it was recorded to be 77 yards (70 m) around and 18 yards (16 m) in "conical height", with forty-two "pillar stones" or kerbstones around the edge. The cairn would have had a well-defined shape when it was built. Still, over time it has slipped and been damaged by visitors. Irish folklore holds that it is bad luck to damage such cairns. Some of its stones have been piled into smaller cairns on top of it, which led to the summit being nicknamed 'The Twelve Cairns'. Traditionally, people would gather on the summit at Lughnasadh where they would add a stone to one of the cairns. They would collect and eat bilberries and there would be folk music, dancing and games.