RAAF High Frequency Direction Finding Station
RAAF Yadgin. Australian Special Wireless Group
- Radar/signal station
- Atherton Tablelands
Shead Road, Kairi 4872
The RAAF High Frequency Direction Finding (HF/DF or “Huff Duff”) Station was built as an aviation navigational aid during 1942, and was later used by the Australian Special Wireless Group (ASWG) for intelligence gathering purposes. It is located between Tolga and Kairi, on the north side of Shead Road, northwest of the junction with Yadgin Road.
The site comprises two reinforced concrete buildings. One is a concrete room, 6.3 metres by 3.35 metres and about 2.8 metres high, which housed a power generating plant. This building contains a doorway and one window, and is now incorporated under a large open workshop.
A second concrete building is located in open farm land about 200 metres to the north-west. This round building, called the Set Room, housed the HF/DF receiver console, and is constructed of concrete with a flat roof. The interior was formerly lined with a ‘caneite’ type board which was fixed to timber battens on the walls and roof. The Set Room, 4.4 metres in diameter, 3 metres high, with walls and roof 400mm thick, has one doorway (with a recent steel door) and four high ventilation openings screened by steel louvres. The four vertical antennae and copper mat earthing system have been removed.
The Atherton Tableland was chosen as the site of a major concentration of troops and stores during 1943, for a number of reasons. It was close to New Guinea; near a port (Cairns); had a cooler climate yet was suitable for training in jungle warfare; and it was a mostly malaria-free area for the hospitalisation of those suffering from tropical diseases. The physically exhausting terrain and climate of New Guinea meant that Australian troops had to be regularly rested and rehabilitated, preferably close to their theatre of operations. From December 1942 the headquarters of the Australian Army in north Queensland transferred from Townsville to the Atherton Tableland, with the main administrative base established around the town of Atherton and the nearby settlement of Tolga.
The build up of troops in the area would have been matched by an increase in air activity, and the need for military navigational aids. Development of High Frequency Direction Finding (HF/DF) stations in Australia was underway during the mid 1930s with the growth of commercial aviation and a network of civil HF/DF stations had been established in Queensland before Japan’s entry into the war in December 1941.
The idea of using two or more radio receivers to find the bearings of a radio transmitter and with the use of simple triangulation find the approximate position of the transmitter, had been widely known and used since the early 1900s. The general principle was to rotate a directional aerial and note where the signal was strongest when pointing directly towards and directly away from the transmitting source. Two or more bearings from different locations were recorded and the intersections plotted.
The Bellini-Tosi Medium Frequency (MF) direction finding receiver was the first radio aid to navigation used in Australia, from 1935. Bellini Tosi MF direction finding receivers were installed along the major internal air routes before the age of radio beacons. With this equipment the operator could determine the direction of a radio signal transmitted from an aircraft and relay the bearing back to the pilot.
From 1938–39, new High Frequency Cathode Ray Direction Finding (HF CR DF) units were installed to replace the early Bellini-Tosi MF equipment. These were Marconi-Adcock HF CR DF sets developed in Britain where the system was known as HF/DF or ‘Huff Duff’. The receiver console was housed in a small hut with four vertically polarised 6 metre (20 feet) high antennae installed in the ground on each side of the building, in the form of a square.
Adcock-type HF/DF sets were installed as aviation navigational aids on major commercial air routes through Darwin, Groote Eylandt, Karumba, Cloncurry, Cooktown, Townsville, Rockhampton, Archerfield, Port Moresby and Salamaua. Using the Marconi-Adcock system, bearings taken within a 150 km radius were accurate to three degrees and aircraft could 'home' on the DF station when other aids were not available.
In response to the war in the South West Pacific, RAAF HF/DF stations were built during 1942 at Julia Creek, Mingela, Moongobulla, and Kairi. Other sites of RAAF HF/DF or Very High Frequency (VHF/DF) Stations in Queensland during World War II included Higgins, Cooktown, Karumba, Rockingham, Garbutt, Brandon, Charters Towers, Mackay, Rockhampton, Bundaberg, Archerfield, Amberley and Lowood.
The Kairi HF/DF station was operational by 15 October 1942 on farm land between Kairi and Tolga. Unlike civil HF/DF stations, its component structures were built of reinforced concrete. The facility consisted of two reinforced concrete buildings with 400 mm thick walls located in an open field. One of the buildings housed a power generator plant. The receiver console was housed inside a round concrete building, referred to as the 'Set Room', which stood about 200 metres north-west of the generator building. The Set Room was originally equipped with four vertical aerials, referred to as a Marconi-Adcock Aerial System. Buried beneath the round concrete building was an earthing system consisting of a large copper mat extending two hectares around it. The main camp for personnel was located in a wooded area about 500 metres south.
By late 1943 other HF/DF stations had been established closer to the New Guinea frontline, and the Kairi HF/DF Station was vacated by the RAAF on 24 November 1943. The facility was subsequently occupied by a unit of the Army’s Australian Special Wireless Group (ASWG) which took over the operation of the station for intelligence gathering purposes. A role of ASWG was the monitoring of Australian Army communications to audit security. The group was also responsible for intercepting Japanese wireless transmissions and counter measures against clandestine transmissions within Australia. Finding the location of radio and radar transmitters was one of the fundamental disciplines of Signal Intelligence (SIGINT).
In April 1942 a combined Allied SIGINT agency for the Pacific, the Central Bureau of the Allied Intelligence Bureau, was activated in Melbourne under US and Australian command. During World War II the main north Australian monitoring stations for intercepting Japanese radio communications were located at Darwin, Townsville and Brisbane. The Queensland headquarters of ASWG was at Kalinga army camp in Brisbane (with the ASWG buildings being located at Kedron Park, west of Shaw Road).
It is not known when the Kairi HF/DF facility finally closed. ASWG scaled down its operations at the end of the Pacific war and had shifted its Queensland headquarters to Cabarlah, north of Toowoomba, by 1947.
Kairi High Frequency Direction Finding Station, Reported Place 30353, Queensland Heritage Register.
National Archives of Australia, ET339. RAAF Bones Knob and Yadgin, Tolga - Electrical reticulation, 1942–1945.