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Harold A. Zahl
zahl radar adelbert

1. Introduction

Harold Adelbert Zahl (August 24, 1904 – March 11, 1973) was an American physicist who had a 35-year career with the U.S. Army Signal Corps Laboratories, making major contributions to radar development.

2. Career and Accomplishments

Harold Zahl was born in Chatsworth, Illinois, the son of an Evangelical minister. While still in high school, he became an amateur radio operator (call letters 6BHI). He graduated in physics and mathematics from North Central College in Naperville, Illinois, in 1927, and then attended the University of Iowa where he earned the M.A. degree in 1929 and the Ph.D. degree in 1931, both in solid-state physics.[1]

Upon completing his doctorate, Zahl joined the staff of the Signal Corps Laboratories (SCL) at Fort Monmouth, New Jersey,[1] which later became a part of the Army Research Laboratory.[2] At the same time, he was commissioned a first lieutenant in the U.S. Army Signal Corps.

Zahl's initial work at the SCL was in research on detecting aircraft using thermal radiation from their engines. In 1934, he filed a patent application on "The Art of Locating Objects by Heat Radiation." Initially held up because of its classified nature, this was eventually granted in 1946. In 1936, the SCL started research in Radio Position Finding (RPF – later called radar). Zahl participated in the development of the Army's first fielded RPF system, the SCR-268.

While the SCR-268 was being completed, development of an improved RPF system started and Zahl, now a major, was assigned to lead the effort. To use a common antenna for both transmitting and receiving, Zahl invented a gas-discharge device, called a duplexer. Two configurations of the RPF emerged: the SCR-270 (mobile) and the SCR-271 (fixed-site). These systems started to be fielded in 1940, and were used throughout the war.

The early systems had large antennas. To reduce their size, a transmitter tube that could produce high-power signals at a much higher frequency was needed (antenna size is inversely proportional to frequency). Zahl developed such a tube in 1939. Called the VT-158, it was capable of 240-kW pulsed power at up to 600 MHz. After the start of World War II, this tube formed the base of the AN/TPS-3, a light-weight, portable. early-warning radar, and a companion the AN/TQS-3, a mortar-detection radar. A total of about 900 of these sets were built and used extensively by the Army, particularly in the Pacific Theater. (The name 'radar' took the place of 'RPF' in 1940.)

The SCL reorganized in 1942, and the radar activities became the Camp Evans Signal Laboratory. For the next several years, Zahl worked closely with the Radiation Laboratory at MIT in their development of microwave radars. He was promoted to lieutenant colonel. At the close of the war, he resigned his commission and became a civilian employee at Camp Evans.

In 1948, Zahl was named director of research, and remained in this position until retiring in 1966. During these years, he made many personal contributions to advancing electronic technologies.

Zahl was a resident of Holmdel Township, New Jersey, where he owned the Hazienda Evergreen Plantation, and died at Riverview Hospital in Red Bank on October 12, 1973.[3]

In 1999 construction was completed on a building dedicated to Zahl, called the Zahl Physical Sciences Facility at the Army Research Laboratory in Adelphi, MD.[4] As of 2018, the Zahl building housed ARL's Sensors and Electron Devices Directorate (SEDD).[5]

3. Zahl Tube

Dr. Harold A. Zahl developed a vacuum tube, called the Zahl tube, while working at the Signal Corps Laboratories in the 1930s. The Zahl tube was a major component of the TPS-3 Lightweight Radar, known as the “Tipsy Three,” and the TPQ-3 mortar locating set. The invention made single antenna systems possible for Army and Air Corps early warning radars.[6] The Zahl tube was used during World War II and the Korean War.[7]

3.1. Background

The Zahl tube was designed as a component of radar systems, which detected low–flying aircraft and trace sources of mortar fire.[7] The need for improved high frequency radar arose in the 1940s out of concern for the protection of Panama Canal after the bombing of Pearl Harbor.[7] The Zahl tube was used both in the Pacific and Europe during World War II.[8] Zahl was awarded the Legion of Merit in 1946 for his work with radar and vacuum tubes.[6]

The tube consisted of four triode tubes connected in parallel. The tube envelope contained a tuned plate and grid lines which made it an oscillator. 250,000 watts of peak power could be extracted during a radar pulse.[6][7]

3.2. History

In 1942, Zahl was charged with increasing the frequency of existing radar technology and reducing the size of bulky equipment. He was commissioned to develop new radar tubes for Army ground forces and Air Corps. Zahl also developed entire radar sets, beacons, Identification Friend or Foe (IFF) and other equipment.[6]

Zahl began development of AN/TPS-3, known as "Tipsy Three," in 1942. The Zahl tube was a major component in its design. AN/TPS-3 was the first radar set to operate at high power, 600 -megacycle range. It began with a crash program to construct a small number of the secret radars at Camp Evans Signal Laboratory in New Jersey, and was later flown into combat.[7] The tube sent out radar waves with fifty centimeter wavelengths at its target.[6]

The Zahl tube, called VT-158, was mass produced by Eitel-McCullough, Inc., a manufacturer of high–frequency transmitting tubes located near San Francisco. The tube was also manufactured by Machlett Laboratories. The exact number of VT -158's produced during the war is unknown.[7]

Initial experimentation with an enemy mortar and artillery locating radar was conducted at Camp Evans, New Jersey in 1944. The objective of this program was to develop and field a radar system capable of detecting and locating hostile weapons with sufficient speed and accuracy to permit rapid and effective counter fire by friendly forces. A team of scientists combined the Zahl tube with a new generator, creating a first prototype radar unit for mortar detection, AN/TPQ-3. During the D-Day invasion at Normandy, 24 units protected soldiers from Luftwaffe fighter attacks.[6] The AN/TPQ-3 mortar locater and Zahl tube continued to be used through the Korean War.[7]

4. Recognition

  • IEEE Harry Diamond Award, 1954 "For his technical contributions, his long service, and his leadership in the U.S. Army Signal Corps research program."
  • Department of the Army Decoration for Exceptional Civilian Service[9]
  • Legion of Merit[9]

5. Bibliography

  • Zahl, Harold A. (September 1930). "Reflection of Cadmium and Zinc Atoms from Sodium Chloride Crystals". Physical Review Letters (APS) 36 (5): 893–903. doi:10.1103/PhysRev.36.893. Retrieved 12 June 2015. 
  • Zahl, Harold A.; Golay, Marcel J. E. (1946). "Pneumatic Heat Detector". Review of Scientific Instruments (AIP Publishing) 17 (12). doi:10.1063/1.1770416. Retrieved 12 June 2015. 
  • Zahl, Harold A.; Marchetti, John W. (January 1946). "Radar on 50 Centimeters – The TPS-3 Radar". Electronics (McGraw–Hill): 98–104. ISSN 0013-5070. Retrieved 12 June 2015. 
  • Zahl, Harold A. (February 1952). "Physics in the Signal Corps". Physics Today (AIP) 5 (2): 16. doi:10.1063/1.3067477. Retrieved 13 June 2015. 
  • Zahl, Harold A.; Reilley, Edward M. (August 1958). "Exploratory research". Physics Today (AIP) 11 (8): 20. doi:10.1063/1.3062684. Retrieved 13 June 2015. 
  • Zahl, Harold A.; Ziegler, Hans K. (January 1960). "Power sources for satellites and space vehicles". Solar Energy (Elsevier) 4 (1): 32–38. doi:10.1016/0038-092X(60)90047-5. Retrieved 12 June 2015. 
  • Zahl, Harold A. (April–July 1960). "From an Early Sputnik Diary". Military Electronics, IRE Transactions on (IEEE) MIL-4 (2–3): 320–322. doi:10.1109/IRET-MIL.1960.5008242. Retrieved 12 June 2015. 
  • Zahl, Harold A. (October 1960). "One Hundred Years of Research". Military Electronics, IRE Transactions on (IEEE) MIL-4 (4): 397–401. doi:10.1109/IRET-MIL.1960.5008264. Retrieved 12 June 2015. 
  • Zahl, Harold A. (November 1960). "Signal Corps centennial". Physics Today (AIP) 13 (11): 34. doi:10.1063/1.3056707. Retrieved 13 June 2015. 
  • Zahl, Harold A. (March 1961). "Looking Backward toward Tomorrow". Aerospace and Navigational Electronics, IRE Transactions on (IEEE) ANE-8 (1): 3–6. doi:10.1109/TANE3.1961.4201770. Retrieved 12 June 2015. 
  • Zahl, Harold A. (May 1962). "Fifty Years of Teaching Machines". Proceedings of the IRE (IEEE) 50 (5): 575–578. doi:10.1109/JRPROC.1962.288366. Retrieved 12 June 2015. 
  • Zahl, Harold A. (1968). Electrons away;: Or, Tales of a government scientist. Vantage Press. 
  • Miller, Ronald I.; Snouse, Tom; Zahl, Harold A.; Clancy, Edward P. (April 1970). "More on employment". Physics Today (AIP) 23 (4): 10. doi:10.1063/1.3022056. Retrieved 13 June 2015. 
  • Zahl, Harold A. (December 1970). "A Tale of Two Crises". Signal Magazine. Retrieved June 12, 2015. 
  • Zahl, Harold A. (1972). Radar Spelled Backwards. Vantage Press. 
Further Reading
In this part, we encourage you to list the link of papers wrote by the character, or published reviews/articles about his/her academic contributions. Edit


  1. "Harold A. Zahl, Director, 1949". Proceedings of the IRE (IEEE) 37 (5): 466. May 1949. doi:10.1109/JRPROC.1949.232321. Retrieved 12 June 2015. 
  2. (in en) History of the U.S. Army Research Laboratory. Government Printing Office. ISBN 9780160942310. 
  3. "DR. HAROLD ZAHL, 68, ARMY RESEARCHER". New York Times. March 12, 1973. Retrieved June 30, 2014. 
  4. "Building ARL, 1993-1998 | U.S. Army Research Laboratory" (in en). 
  5. (in en) History of the U.S. Army Research Laboratory. Government Printing Office. ISBN 9780160942310. 
  6. Comm'd, Army (U S. ), CECOM Life Cycle Management (2010-10-25) (in en). A History of Army Communications and Electronics at Fort Monmouth, New Jersey, 1917-2007. Government Printing Office. ISBN 9780160869105. 
  7. "Secret Story of the VT-158". Popular Electronics. March 1964. 
  8. (in en) History of the U.S. Army Research Laboratory. Government Printing Office. ISBN 9780160942310. 
  9. "Dr. Harold A. Zahl Dies, Former Dir. of Research". The Monmouth Message. March 15, 1973. Retrieved June 13, 2015. 
Name: Harold A. Zahl
Born: Aug 1904
Died: Mar 1973
Chatsworth, Illinois, U.S.
Title: Physicist
Affiliation: Unknown
Honor: Unknown
Subjects: Others
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Entry Collection: HandWiki
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Update Date: 08 Dec 2022
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