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Trevor Lloyd Wadley, (1920 – 21 May 1981) was a South African electrical engineer, best known for his development of the Wadley Loop circuit for greater stability in communications receivers and the Tellurometer, a land surveying device.
He then went to Howard College (now the University of KwaZulu-Natal), where he studied under Hugh Clark and Eric Phillips, after which he completed his Thesis (D.Sc.) at the University of the Witwatersrand, Faculty of Science, 1959, Heterodyne techniques in specialised radio instrumentation . He had the habit of rarely, if ever, taking notes in lectures due to his near-eidetic memory. GR Bozzoli noted in is book Forging Ahead – South Africa’s Pioneering Engineers that Wadley "would very occasionally take out a small pocket notebook and write a word or two in it using a blunt, stubby pencil. His remarkable mind understood and remembered every item of a lecture".
In 1941, during World War II, he joined the Special Signals Services (SSS) of the South African Corps of Signals which was engaged in developing South Africa's own radar system based on the British experience which had been communicated to them. Wadley and other colleagues including Jules Fejer, the Hungarian-born mathematician, were trained on the British radar project. His association with Fejer would continue for many more years. Wadley was not keen on mathematics but Fejer proved each of Wadley's concepts mathematically.
In 1946, Wadley was employed as a designer of radio equipment and instrumentation in a special division of the Telecommunications Research Laboratory (TRL), created at the behest of Prime Minister Jan Smuts and located at the electrical engineering department of the University of the Witwatersrand (under Basil Schonland). The TRL relocated to the South African Council for Scientific and Industrial Research (CSIR) and was renamed the National Institute for Telecommunications Research (NITR) (under Dr Frank Hewitt).
In 1948, Wadley started working on an urgent project for the South African Chamber of Mines to provide a means of radio communication underground for rescue purposes. After a feasibility investigation Wadley wrote a report indicating that it could be done and detailing his recommendations. The Chamber did not pursue the matter for more than a decade.
Wadley retired in 1964 (aged 44) and lived on the south coast of KwaZulu-Natal until his death from cancer in 1981 (aged 61).
A Wadley receiver (circa 1952) is on display at the South African Institute of Electrical Engineers historical collection in Observatory, Johannesburg.
The Tellurmeter could measure up to a distance of 80 km by measuring the time delay in microwave transmissions. It was used in land surveying but has been mostly replaced with laser-based systems. The replacement to the microwave tellurometer was also developed by a South African, H.D. Hölscer. Miniaturised versions are still used in some surveying instruments and mine lift-shafts.
One of the first test of the tellurometer involved a measurement of the distance between Brixton Hill in Western Johannesburg and Fort Klapperkop in Pretoria, this being the most accurately known survey baseline in South Africa at the time. It successfully proved the accuracy of the tellurometer but, over time, Wadley noticed a bias to the measurements he was obtaining. He ascribed these to an inaccurate value of the speed of light that had been supplied to him. He approached the National Physical Laboratory in Teddington in England and they agreed to do a new measurement of the speed of light. The new measurement vindicated Wadley's claim. In 1958 the Tellurometer was used to measure Manhattan (13.08 miles). The measurement took 1 hour (plus two hours for the technicians to move from the south end of the island to the north.) Previously the measurement had taken 5 days. Official website
When the system was demonstrated in England before a group including the British Prime Minister, Harold Macmillan, it showed that a line on the Salisbury Plain which had been used as the baseline for British surveying had been incorrectly calculated by 1.5 meters. Subsequent sales of the device earned more than R300 million (in 1960's terms) in foreign revenue for South Africa. Tellurometers are still manufactured in Plumstead, South Africa. Manufacturer of tellurometers website
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