Tellurometer EDM (Tellurometer MRA 1)

The first successful microwave EDM was invented by Col. Harry A. Baumann of the South African Trigonometrical Survey, developed by Trevor Lloyd Wadley of the Telecommunications Research Laboratory of the South African Council for Scientific and Industrial Research (CSIR), and manufactured by Tellurometer Pty. Ltd. in Cape Town. The Tellurometer was designed to yield geodetic accuracy over geodetic distances, but it was also useful for second-order work, especially in areas where the terrain was rough and/or the temperatures extreme.
The original Tellurometer, known as the Micro-Distancer M/RA 1, used a continuous wave at 3,000 megahertz, modulated by 10 megahertz and three other nearby frequencies. The remote station reradiated the incoming wave in a similar wave of more complex modulation, and the resulting phase shift was a measure of the distance traveled. The results appeared on a cathode ray tube with circular sweep. This instrument could penetrate haze and mist in daylight or darkness, and had a normal range of 30-50 km. It was covered by patents in at least eleven countries granted to Wadley and assigned to the CSIR; the U.S. patent (#2,907,999) was entitled "Determining Relative Position by Means of Transit Time of Waves."
The new instrument was unveiled in Constantia, South Africa, in January 1957. By early April, after the first public trials, The Engineer opined that Tellurometer "is likely to become one of the fundamental instruments of the geodetic surveyor's equipment, since it enables rapid measurement of, for instance, a base line, which might take several weeks to measure by conventional methods." By 1962, the Tellurometer was said to have "revolutionized survey operations, increasing the output of work, and making possible various projects "which would have been virtually impossible in pre-Tellurometer days."
The U.S. Coast & Geodetic Survey sent a Tellurometer to Alaska in June 1957 to survey the south coast of Atka Island in the central Aleutians, and found that it performed well even in "rugged terrain, dangerous surf, and adverse weather conditions." By midsummer this instrument had been sent to Virginia to establish the scale for the photogrammetric surveys made in connection with the Federal Highway Program that had been enacted into law in 1956. The Army purchased several hundred Tellurometers, most of them modified to military specifications.
Tellurometers were also used by surveyors in private practice. The one at the Smithsonian was purchased by Maddox & Hopkins, and used originally in the Killington, Vt. ski area. One unit is marked "MASTER Micro-Distancer Model M/RA 1--Serial No. MA 81." The other is marked "REMOTE Micro-Distancer Model M/RA 1--Serial No. RA 107." Both are also marked "Made in the Union of South Africa by TELLUROMETER (Pty. Ltd.) Box 2023 Cape Town." The instrument was probably made before the introduction of Model M/RA 3 in 1963.
Ref: T. L. Wadley, "The Tellurometer System of Distance Measurement," Empire Survey Review (July 1957): 100-110, and (October 1957): 146-159.
Tellurometer, Simplified Instructions for Use of the Tellurometer "Micro-Distancer" Models MRA-1, MRA-1/CW, and MRA-2
Austin Poling, Tellurometer Manual (Washington, D.C.: Government Printing Office, 1959; second edition, 1961).
Currently not on view
Object Name
place made
South Africa: Western Cape, Province of the, Cape Town
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accession number
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Medicine and Science: Physical Sciences
Measuring & Mapping
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center


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