Finishing its wartime role in January 1946, and taken over in 1947 by the Government Communication Headquarters, the station at Ginahirk was one of 3 listening stations around the UK built in 1942 to intercept enemy wireless communications in conjunction with the code-breakers at Bletchley Park. Closed as a listening station in 1978, Gilnahirk appears to have remained in civil service hands and been used for medical record storage. The site was renovated in 2010 and is now residential accommodation. I visited in 2008 prior to the renovation, and the images show many of the post-war buildings and features along with the state of decay and abandonment.
The location of the Adcock Direction Finding Equipment is still not known. This unique piece of equipment consisted of a metal tank, sitting just below ground level, connected to a large array of directional radio antenna, this facility would have been able to pin point the direction of any wireless broadcast within minutes of receiving the frequency. The combination of at least 2 of these bearings from other sites around the UK would triangulate the source of any transmission.
A fascinating account of the work done at the Y Station at Gilnahirk can be found on the BBC website. The WW2 People’s War is an online archive of wartime memories contributed by members of the public and gathered by the BBC. The archive can be found at bbc.co.uk/ww2peopleswar
“During the run up to WWII the G.P.O. established a radio station on the Castlereagh Hills overlooking Belfast. The site consisted of a few wooden and nissan huts which were surrounded by a considerable number of very tall telegraph poles dotted about the adjoining fields. These poles were linked together with overhead wire and formed the aerial network which was used to intercept the radio traffic of the time. The wooden huts served a number of roles, but one hut would have contained the main radio room. This consisted of eighteen banks of American HRO radio receivers. These receivers were the Rolls Royce of their day and no signal escaped the fine tuning of an HRO receiver. During the establishment of this station a Top Secret Marconi-Adcock Direction finding facility was placed into an all metal tank and then the whole thing was buried just below the ground some distance from the main collection of wooden huts. Four thirty feet high telegraph poles were placed one at each corner of this underground structure.
All this work was carried out by the Royal Corps of Signals and the G.P.O. radio department. The Belfast electricity company supplied a transformer to the site, but the main cable feed for that transformer had to be buried below the ground incase it caused any interference to the signal reception. The G.P.O. also provided an underground high grade telephone cable which allowed the station to be part of a much bigger wartime communications network.” Source