FLR-9

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 on HF communications from almost anywhere on the planet.

Description

The [http://www.premium-rx.org/ref/wullenweber.pdf 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 (Decommissioned)
* San Vito dei Normanni Air Station, ItalyAdvances 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.

Trivia

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

External links

* [http://www.premium-rx.org/ref/wullenweber.pdf AN/FLR-9 Operation and Service manual]
* [http://www.usafsa.org/ USASA Field Station Augsburg] - history of the Augsburg site
* [http://www.sunnysanvito.com/ Sunny San Vito] - membership-only page for former staff of the San Vito site
* [http://cryptome.org/elmen-eyeball.htm Cryptome: Eyeballing the Elmendorf Wullenweber] , Elmendorf Air Force Base
* [http://homepage.ntlworld.com/alan-turnbull/secret.htm#chicksands Extreme close-up hi-res aerial photo of FLR-9 at Chicksands just before being dismantled in 1996]
* [http://us-seasia.tripod.com/id6.html FLR-9 at Camp Ramasun, near Udon Thani, Thailand]
* FLR-9 at Elmendorf AFB, Alaska coord|61.264486|-149.851198|type:landmark|name=FLR-9 at Elmendorf AFB, Alaska
* FLR-9 at Gablingen, Augsburg, Germany coord|48.449278|10.863161|type:landmark|name=FLR-9 at Gablingen, Augsburg, Germany
* FLR-9 at Misawa, Honshū Island, Japan coord|40.720053|141.326580|type:landmark|name=FLR-9 at Misawa, Honshu Island, Japan
* FLR-9 site at Chicksands, Bedfordshire, UK coord|52.042580|-0.388298|type:landmark|name=FLR-9 site at Chicksands, Bedfordshire, UK
* FLR-9 site at Clark AFB, Philippines coord|15.204687|120.528173|type:landmark|name=FLR-9 site at Clark AFB, Philippines
* FLR-9 site at Karamursel AS, Turkey coord|40.709453|29.528074|type:landmark|name=FLR-9 site at Karamursel AS, Turkey
* FLR-9 site at San Vito dei Normanni AS, Italy coord|40.645638|17.841368|type:landmark|name=FLR-9 site at San Vito dei Normanni AS, Italy
* FLR-9 site at Ramasun Station, Udon Thani, Thailand coord|17.292134|102.869024|type:landmark|name=FLR-9 site at Ramasun Station, Udon Thani, Thailand
* [http://www.fas.org/irp/program/collect/an-flr-9.htm AN/FLR-9 information on FAS.org]

ee also

* SIGINT
* HF/DF