AN/FLR-9
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The AN/FLR-9 is a type of very large circular "Wullenweber" antenna array, built at many locations during the cold war for HF/DF direction finding of high priority targets. The worldwide network, known collectively as "Iron Horse", could locate HF communications almost anywhere on the planet. Due to their large size and shape, these units were often nicknamed "Elephant Cages" or "Turkey Farms".
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[edit] Description
The AN/FLR-9 Operation and Service Manual[1] describes the array as follows: "The antenna array is composed of three concentric rings of antenna elements. Each ring of elements receives rf signals for an assigned portion of the 1.5 to 30-MHz radio spectrum. The outer ring normally covers the 2 to 6-MHz range (band A), but also provides reduced coverage down to 1.5 MHz. The center ring covers the 6 to 18-MHz range (band B) and the inner ring covers the 18 to 30-MHz range (band C). Band A contains 48 sleeve monopole elements spaced 78.4 feet apart (7.5 degrees). Band B contains 96 sleeve monopole elements spaced 37.5 feet (11.43 m) apart (3.75 degrees). Band C contains 48 antenna elements mounted on wooden structures placed in a circle around the central building. Bands A and B elements are vertically polarized. Band C elements consist of two horizontally polarized dipole antenna subelements electrically tied together, and positioned one above the other."
The array is centered on a ground screen 1,443 feet (439.8 m) in diameter. The arrangement permits accurate direction finding of signals from up to 4000 nautical miles (7 408 km) away.
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FLR-9s were constructed at the following places:
- Augsburg, Germany
- Chicksands, England
- Clark AB, Philippines
- Elmendorf AFB, Alaska
- Karamursel, Turkey
- 7th Radio Research Field Station/Ramasun Station, Udon Thani Province, Thailand
- Misawa AB, Japan
- San Vito dei Normanni Air Station, Italy
- RAF Edzell, Scotland
Advances in technology have made the FLR-9 almost obsolete. As of 2009, two FLR-9 arrays remain active in Misawa AB, Japan and Elmendorf AFB, Alaska and there are no plans for decommissioning. In 1997, the FLR-9 at the former Clark AB in the Philippines was converted into a 35,000-seat fabric-covered amphitheatre. In late 2001, the U.S. Air Force sought bids for the demolition of the site in San Vito, Italy. The amount was too low so it never went through.
[edit] References
[edit] External links
- AN/FLR-9 Operation and Service manual
- USASA Field Station Augsburg - history of the Augsburg site
- Sunny San Vito - membership-only page for former staff of the San Vito site
- Cryptome: Eyeballing the Elmendorf Wullenweber, Elmendorf Air Force Base
- Extreme close-up hi-res aerial photo of FLR-9 at Chicksands just before being dismantled in 1996
- FLR-9 at Camp Ramasun, near Udon Thani, Thailand
- FLR-9 at Elmendorf AFB, Alaska 61°15′52″N 149°51′04″W / 61.264486°N 149.851198°W
- FLR-9 at Gablingen, Augsburg, Germany 48°26′57″N 10°51′47″E / 48.449278°N 10.863161°E
- FLR-9 at Misawa, Honshū Island, Japan 40°43′12″N 141°19′36″E / 40.720053°N 141.326580°E
- FLR-9 site at Chicksands, Bedfordshire, UK 52°02′33″N 0°23′18″W / 52.042580°N 0.388298°W
- FLR-9 site at Clark AFB, Philippines 15°12′17″N 120°31′41″E / 15.204687°N 120.528173°E
- FLR-9 site at Karamursel AS, Turkey 40°42′34″N 29°31′41″E / 40.709453°N 29.528074°E
- FLR-9 site at San Vito dei Normanni AS, Italy 40°38′44″N 17°50′29″E / 40.645638°N 17.841368°E
- FLR-9 site at Ramasun Station, Udon Thani, Thailand 17°17′32″N 102°52′08″E / 17.292134°N 102.869024°E
- AN/FLR-9 information on FAS.org
