OVERVIEW: The AN/FLR-9 is a HF/DF antenna array for receiving signals intelligence.


DETAILS: THe AN/FLR-9 is a large circular "Wullenweber" antenna array for HF/DF direction finding of high priority targets. The worldwide network could locate HF communications almost anywhere on Earth. 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 1.5to 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). The system permits accurate direction finding of signals up to 4000 nautical miles (7408 km) away.


Specifications:

Frequency: 		1.5-30 MHz
Range:			4000 nm 



NOTES: IOC 1963.  Because of the exceptionally large size of its outer reflecting screen (1056 vertical steel wires supported by 96 120-foot towers), the FLR-9 was commonly referred to by the nickname "Elephant Cage." The worldwide network was collectively known as "Iron Horse."

SOURCES:  US Army, "Operator's Depot Maintenance Manual for Antenna Group AN/FLR-9(V70/(V8), June 1976.  Located at http://www.premium-rx.org/ref/wullenweber.pdf ; 
"AN/FLR-9." Federation Of American Scientists – Science for a Safer, More Informed World. Accessed April 27, 2020. https://fas.org/irp/program/collect/an-flr-9.htm.
