AN/FPS-24 radar

The AN/FPS-24 Radar was a long range early warning radar used by the United States Air Force Air Defense Command. It used a two-frequency signal in order to avoid fluctuation loss, which causes signals on single-frequency radars to fade in and out as the target moves. Reducing this effect results in a much steadier signal.

AN/FPS-24
General Electric AN/FPS-24 Radar
Country of originUnited States
No. built12
Typeearly warning radar
FrequencyVHF
PRF278 Hz
Pulsewidth20 µs
RPM5
Range250 nautical miles (460 km)
Diameter120 by 50 feet (37 by 15 m)
Precision200 m in range
Power5 MW

General Electric was the primary contractor for the design, which operated in the very high frequency (VHF) at 214 to 236 MHz.

Construction

Twelve systems were built between 1958 and 1962 at various locations around the United States. Problems with the design were revealed during initial testing Eufaula AFS (Eufaula, Alabama) in 1960, resulting in modifications. Additional problems occurred in 1961 when deployment of the first production model at Point Arena Air Force Station in California. revealed bearing problems 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 radar sites due to catastrophic damage to the support tower, sail, and feed horn.

Depending on the location of the installation, the radar reflector 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 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 prototype installation at Eufaula, Alabama, was perched atop a steel lattice structure tower of shorter, unconfirmed height. Acme Missiles & Construction Corp., Rockville Centre, N.Y. built the radar tower facilities at Missile Master, Pittsburgh Defense Area, Oakdale, PA.[1] 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.

The AN/FPS-24 radar antenna reflector rotated 5 revolutions per minute (a SAGE specification) and was often the cause of 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 MW 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.

Post-operation

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

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.

References
  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. "Mt. Um". 30 August 2013.

Public Domain This article incorporates public domain material from the Air Force Historical Research Agency.

External references
  • AN/FPS-24 @ radomes.org
  • AN/FPS-24 @ fas.org
  • 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.
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