The US Air Force's over-the-horizon-backscatter (OTH-B) air defense radar system is by several criteria the largest radar system in the world. Six one-million-watt OTH radars see far beyond the range of conventional microwave radars by bouncing their 5-28-MHz waves off the ionosphere, an ionized layer about 200 km above the earth. It was developed over 25 years at a cost of $1.5 billion to warn against Soviet bomber attacks when the planes were still thousands of miles from US air space.
The West Coast Sector included an operations center at Mountain Home Air Force Base, Idaho, the transmitter at Christmas Valley, Oregon [43°16'00"N 120°21'40"W], and the receiver at Tule Lake, near Alturas, California. GE Aerospace was initially awarded a contract valued at $145 million for the first two sectors of the West Coast system, with an additional contract for the third sector for $56 million awarded in November 1987. The total value of the West Coast system contract was expected to be approximately $313 million. The system was turned over to the USAF at the end of 1990 for operational tests and evaluation.
With the end of the Cold War, just months after their deployment, the three OTH radars on the West Coast were mothballed. The Air Force maintains the six East Coast and West Coast OTH-B radars in a state called "warm storage," which preserves the physical and electrical integrity of the system and permits recall within 24 months.
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