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 world-wide network, known collectively as "Iron Horse", could locate on HF communications from almost anywhere on the planet.

Contents 1 Description 2 Trivia 3 External links 4 See also

[edit] Description

The AN/FLR-9 Operation and Service manual 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.

FLR-9s were constructed at the following places:

• Augsburg, Germany
• Chicksands, England
• Clark AFB, Philippines
• Elmendorf AFB, Alaska
• Karamursel, Turkey
• 7th Radio Research Field Station/Ramasun Station, Udon Thani Province, Thailand
• Misawa Air Base, Japan
• Torii Station, Okinawa
• San Vito dei Normanni Air Station, Italy

Advances in technology have made the FLR-9 obsolete. Two FLR-9 arrays remain in use in 2007, although they are expected to be decommissioned soon. In 1997, the FLR-9 at the former Clark AFB 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.

[edit] Trivia

Due to their size and shape, these units were often nicknamed "Elephant Cages".

[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, -149.851198 (FLR-9 at Elmendorf AFB, Alaska)
• FLR-9 at Gablingen, Augsburg, Germany 48°26′57″N 10°51′47″E / 48.449278, 10.863161 (FLR-9 at Gablingen, Augsburg, Germany)
• FLR-9 at Misawa, Honshu Island, Japan 40°43′12″N 141°19′36″E / 40.720053, 141.326580 (FLR-9 at Misawa, Honshu Island, Japan)
• FLR-9 site at Chicksands, Bedfordshire, UK 52°02′33″N 0°23′18″W / 52.042580, -0.388298 (FLR-9 site at Chicksands, Bedfordshire, UK)
• FLR-9 site at Clark AFB, Philippines 15°12′17″N 120°31′41″E / 15.204687, 120.528173 (FLR-9 site at Clark AFB, Philippines)
• FLR-9 site at Karamursel AS, Turkey 40°42′34″N 29°31′41″E / 40.709453, 29.528074 (FLR-9 site at Karamursel AS, Turkey)
• FLR-9 site at San Vito dei Normanni AS, Italy 40°38′44″N 17°50′29″E / 40.645638, 17.841368 (FLR-9 site at San Vito dei Normanni AS, Italy)
• FLR-9 site at Ramasun Station, Udon Thani, Thailand 17°17′32″N 102°52′09″E / 17.292134, 102.869024 (FLR-9 site at Ramasun Station, Udon Thani, Thailand)
• AN/FLR-9 information on FAS.org

[edit] See also

• SIGINT
• HF/DF