Sunday, February 22, 2015

End of an Era

The videos near the end of this post highlight the end of an era. An era that not a lot of people know about. The AN/FLR-9 or Elephant Cage (called that due to its size) is a HF Rombic Antenna that was used exclusively by the Electronic Security Command (what it was called when I served) in its mission to provide national and tactical level Signals Intelligence or SIGINT. Also, during my time, the antenna was coupled to the R-390 receivers and later the RACALs. Before my time the R-388 was the mainstay receiver and I have one in service in my shack that I use very often. 

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 in diameter. The arrangement permits accurate direction finding of signals from up to 4000 nautical miles away.

FLR-9s were constructed at the following places:

Augsburg, Germany

Chicksands, UK

Clark AB, PI

Elmendorf, Alaska

Karamursel, Turkey

Udon, Thani Province, Thailand

Misawa AB, Japan

San Vito, Italy

The dismantling of the FLR-9 at Misawa is on-going and due to be completed this year (2015). The last AN/FLR-9 in existence is at Elmendorf AFB Alaska. 

Enough distractions, I need to complete a couple of End Fed HF antenna designs for portable use.


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