GEIS #1 Solution

We have a winner to GEIS #1! Shanafme from over at Shanafeltsector has come up with the answer.

Solution:

The AN/FLR-9 is a type of very large circular “Wullenweber” antenna array, built at many locations during the cold war to gather signals for western signals intelligence (SIGINT). The world-wide network, known collectively as “Iron Horse”, could eavesdrop on HF communications from almost anywhere on the planet.

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 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.

-via Wikipedia entry on FLR-9

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2 Responses to GEIS #1 Solution

  1. Jerky says:

    What did you say the prize was again? 🙂

  2. AxsDeny says:

    My undying love and affection. Or possibly credit where it’s due. Take your pick. 😉

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