This is an interesting Video. On the Development of, Over The Horizon Backscatter Radar. Check out the related videos too...

Don

AN/FPS-118 Over-The-Horizon-Backscatter (OTH-B) Radar

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Video link...
https://www.youtube.com/watch?v=2GVPdJzfiJE

Uploaded on Dec 5, 2009

The USAF's Rome Laboratory had the first US success with their AN/FPS-118 OTH-B. A prototype with a 1 MW transmitter and a separate receiver was installed in Maine, offering coverage over a 60 degree arc between 900 to 3,300 km. A permanant transmitting facility was then built in Moscow, Maine, a receiving facility in nearby Columbia Falls, and an operational center between them in Bangor. The coverage could be extended with additional receivers, providing for complete coverage over a 180 degree arc (each 60 degree portion known as a "sector"). GE Aerospace was awarded the development contract, expanding the existing east coast system with two additional sectors, while building another three-sector system on the west coast, a two-sector system in Alaska, and a one-sector system facing south. In 1992 the Air Force contracted to extend the coverage 15 degrees clockwise on the southern of the three east coast sectors to be able to cover the southeast US border. Additionally, the range was extended to 3000 miles, crossing the equator. This was operated 40 hours a week at random times. Radar data was fed to the U.S. Customs/Coast Guard C3I Center, Miami; Joint Task Force 4 Operations Center, Key West; U.S. Southern Command Operations Center, Key West; and U.S. Southern Command Operations Center, Panama.

With the end of the cold war, the influence of the two senators from Maine was not enough to save the operation and the Alaska and southern-facing sites were canceled, the two so-far completed western sectors and the eastern ones were turned off and placed in "warm storage," allowing them to be used again if needed.