AN/FPS-24 Radar

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AN-FPS-24 Radar.jpg
General Electric AN/FPS-24 Radar
Country of originUnited States
TypeLong Range Search Radar

The AN/FPS-24 Radar was a Long Range Search Radar used by the United States Air Force Air Defense Command.

General Electric was the prime contractor this frequency diverse (FD) long range search radar designed to operate in the Very High Frequency (VHF) at 214 to 236 MHz. There were problems with this radar at the test site at Eufaula AFS (Eufaula, Alabama) in 1960. These problems required many modifications. Acme Missiles & Construction Corp., Rockville Centre, N.Y. built the radar tower facilities at Missile Master, Pittsburgh Defense Area, Oakdale, Pa.[1]

Additional problems occurred when deployment was attempted in 1961 with the first production model at Point Arena Air Force Station in California. When the radar finally deployed, bearing problems often occurred due to the 85.5 short tons (77.6 t) antenna weight. Failures of the 9 feet (2.7 m) hydrostatic bearing often caused the early closure of some sites due to catastrophic damage to the support tower, sail, and feed horn.

Twelve systems were built between 1958 and 1962. The prototype at Eufaula, Alabama, was perched atop a steel lattice structure tower of shorter (but unconfirmed) height. Depending on the location it was to be deployed in operational production, the radar antenna (sail) itself was perched atop one of two different towers: a cast-in-place concrete tower or a metal-sided steel-framed tower both with equal dimensions of 84.5 feet (25.8 m) in height and side dimensions of 60.25 feet (18.36 m) square (63.25 inches (1,607 mm) square when including the thickness of corner buttresses). This tower design was also used for the AN/FPS-35 frequency diverse SAGE (Semi-Automatic Ground Environment) search radar built by Sperry Corporation. The AN/FPS-24 radar antenna sail rotated 5 revolutions per minute (a SAGE specification) and was often the cause of microwave interference reported by nearby residents who could hear the radar signal in television and radio broadcasts. At some locations, the radar signal was "blanked" as it passed over television broadcast antenna sites such as Mt. Loma Prieta in the Santa Cruz Mountains, California. However, at DEFCON 3 or higher, the signal was ordered "unblanked" in all directions. The 7.5 Megawatt (maximum power) transmitter ran in normal operation at 5 Megawatt output pulse (nearly 20 microseconds in duration) and was conveyed from the transmitter to the antenna feed horn via a 9 inches (230 mm) diameter rigid coaxial connector. The feed horn consisted of a cross dipole antenna design for both A and B channels.

In operation[edit]

Two of the AN/FPS-24 radar installations were covered by a fiberglass dome, protecting the components from the elements. One such installation was at Cottonwood Air Force Station, Idaho. The other was at Mt Hebo Air Force Station, Oregon.


Subsequent to USAF site closures, some AN/FPS-24 radar units were upgraded to Air Route Surveillance Radar (ARSR) units for USAF-FAA joint surveillance duty.

Historical Designation[edit]

On May 10, 2016, the Santa Clara County Board of Supervisors voted unanimously to list the Almaden Air Force Station AN/FPS-24 concrete Radar Tower on the County Heritage Resource Inventory, thus giving it official historic status and demolition protection.[2]

FPS-24 radome dwarfing FPS-6A radome alongside, Cottonwood AFS, Cottonwood, Idaho circa 1964.

The 84.5 foot (25.8 m) concrete buildings that supported most of the AN/FPS-24 antennas were prominent landmarks,[3] and all remain standing.


  1. ^ Missiles and Rockets, April 17, 1961, p. 50.
  2. ^ "Mount Umunhum cube to stay: Cold War relic gets historic designation". San Jose Mercury News. 10 May 2016. Retrieved 25 May 2016.
  3. ^ [1]

 This article incorporates public domain material from the Air Force Historical Research Agency website

External references[edit]

  • AN/FPS-24 @
  • AN/FPS-24 @
  • Winkler, David F. (1997), Searching the skies: the legacy of the United States Cold War defense radar program. Prepared for United States Air Force Headquarters Air Combat Command.

External links[edit]