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Horn Antenna
(U.S. National Register of Historic Places)
Location:	Holmdel, New Jersey  United States
Built/Founded:	1959
Added to NRHP:	1990

The Horn Antenna, at Bell Telephone Laboratories in Holmdel, New Jersey, is listed as a National Historic Landmark because of its association with the research work of two radio astronomers, Arno Penzias and Robert Wilson. In 1965 while using the Horn Antenna, Penzias and Wilson stumbled on the microwave background radiation that permeates the universe. Cosmologists quickly realized that Penzias and Wilson had made the most important discovery in modern astronomy since Edwin Hubble demonstrated in the 1920s that the universe was expanding. This discovery provided the evidence that confirmed George Gamow's and Abbe Georges Lemaitre's "Big Bang" theory of the creation of the universe and forever changed the science of cosmology--the study of the history of the universe--from a field for unlimited theoretical speculation into a subject disciplined by direct observation. In 1978 Penzias and Wilson received the Nobel Prize for Physics for their momentous discovery^[1].

The Horn Antenna at Bell Telephone Laboratories in Holmdel, New Jersey, was constructed in 1959 to support Project Echo—the National Aeronautics and Space Administration's passive communications satellite project^[2].

The antenna is 50 feet (15 m) in length with a radiating aperture of 20 by 20 feet (6 by 6 m) and is made of aluminum. The antenna's elevation wheel is 30 feet (10 m) in diameter and supports the weight of the structure by means of rollers mounted on a base frame. All axial or thrust loads are taken by a large ball bearing at the apex end of the horn. The horn continues through this bearing into the equipment cab. The ability to locate receiver equipment at the apex of the horn, thus eliminating the noise contribution of a connecting line, is an important feature of the antenna. A radiometer for measuring the intensity of radiant energy is found in the equipment cab.

The triangular base frame of the antenna is made from structural steel. It rotates on wheels about a center pintle ball bearing on a track 30 feet (10 m) in diameter. The track consists of stress-relieved, planed steel plates which are individually adjusted to produce a track flat to about 1/64 inch (0.4 mm). The faces of the wheels are cone-shaped to minimize sliding friction. A tangential force of 100 pounds force (400 N) is sufficient to start the antenna in motion.

To permit the antenna beam to be directed to any part of the sky, the antenna is mounted with the axis of the horn horizontal. Rotation about this axis affords tracking in elevation while the entire assembly is rotated about a vertical axis for tracking in the azimuth.

With the exception of the steel base frame, which was made by a local steel company, the antenna was fabricated and assembled by the Holmdel Laboratory shops under the direction of Mr. H. W. Anderson, who also collaborated on the design. Assistance in the design was also given by Messrs. R. O'Regan and S. A. Darby. Construction of the antenna was completed under the direction of Mr. A. B. Crawford from Freehold Borough, New Jersey.

When not in use, the antenna azimuth sprocket drive is disengaged, thus permitting the structure to "weathervane" and seek a position of minimum wind resistance. The antenna was designed to withstand winds of 100 miles per hour (160 km/h) and the entire structure weighs 18 tons.

The Horn Antenna combines several ideal characteristics it is extremely broad-band, has calculable aperture efficiency, and the back and sidelobes are so minimal that scarcely any thermal energy is picked up from the ground. Consequently it is an ideal radio telescope for accurate measurements of low levels of weak background radiation.

A plastic clapboarded utility shed 10 by 20 feet (3 by 6 m), with two windows, a double door and a sheet metal roof, is found next to the Horn Antenna. This structure houses equipment and controls for the Horn Antenna and is included in this nomination.

The original material in this article was taken from a National Park Service publication which in turn used the following sources:

1. ^ Marcus Chown, "A Cosmic Relic in Three Degrees," New Scientist, September 29, 1988, pp. 51-52.
2. ^ J.S. Hey, The Evolution of Radio Astronomy (New York: Neale Watson Academic Publications, Inc., 1973), pp. 98-99.

1. Richard Learner, Astronomy Through the Telescope (New York: Van Nostrand Reinhold Company, 1981), p. 154.

A.B. Crawford, D. C. Hogg, and L. E. Hunt, "Project Echo: A Horn Antenna for Space Communication," Bell System Technical Journal (July 1961), pp. 1095-1099.

• Aaronson, Steve. "The Light of Creation: An Interview with Arno A. Penzias and Robert W. Wilson." Bell Laboratories Record. January 1979, pp. 12-18.
• Abell, George O. Exploration of the Universe. 4th ed., Philadelphia: Saunders College Publishing, 1982.
• Asimov, Isaac. Asimov's Biographical Encyclopedia of Science and Technology. 2nd ed., New York: Doubleday & Company, Inc., 1982.
• Bernstein, Jeremy. Three Degrees Above Zero: Bell Labs in the Information Age. New York: Charles Scribner's Sons, 1984.
• Chown, Marcus. "A Cosmic Relic in Three Degrees," New Scientist, September 29, 1988, pp. 51-55.
• Crawford, A.B., D.C. Hogg and L.E. Hunt. "Project Echo: A Horn-Reflector Antenna for Space Communication," The Bell System Technical Journal, July 961, pp. 1095-1099.
• Disney, Michael. The Hidden Universe. New York: Macmillan Publishing Company, 1984.
• Ferris, Timothy. The Red Limit: The Search for the Edge of the Universe. 2nd ed., New York: Quill Press, 1978.
• Friedman, Herbert. The Amazing Universe. Washington, DC: National Geographic Society, 1975.
• Hey, J.S. The Evolution of Radio Astronomy. New York: Neale Watson Academic Publications, Inc., 1973.
• Jastrow, Robert. God and the Astronomers. New York : W. W. Norton & Company, Inc., 1978.
• Kirby-Smith, H.T. U.S. Observatories: A Directory and Travel Guide. New York: Van Nostrand Reinhold Company, 1976.
• Learner, Richard. Astronomy Through the Telescope. New York: Van Nostrand Reinhold Company, 1981.
• Penzias, A.A., and R. W. Wilson. "A Measurement of the Flux Density of CAS A At 4080 Mc/s," Astrophysical Journal Letters, May 1965, pp. 1149-1154.