John Renshaw Carson was an engineer of transmission theory for the American Telephone and Telegraph Company and the Bell Telephone Laboratories, Inc.
Background
John Renshaw Carson was born on June 28, 1886 in Pittsburgh, Pennsylvania, United States; one of twin sons, the only children of John D. and Ada R. (Johnston) Carson. Their father, of Virginia colonial ancestry, conducted a fancy-grocery business in Pittsburgh.
Education
John was educated in private schools and at Princeton University, where he received the degrees of B. S. (1907), E. E. (1909), and M. S. (1912).
Career
Of rather frail constitution, with some hearing impairment, but with an active mind, Carson concentrated on mathematics and the theoretical side of electrical engineering. His first employment (1909 - 12) was as a student engineer with the Westinghouse Electric and Manufacturing Company, with the General Electric Company, and (as an electrical engineer) with the Jones and Laughlin Steel Company. From 1912 to 1914 he was instructor in physics and electrical engineering at Princeton. In 1914 he became engineer (later engineer of transmission theory) for the American Telephone and Telegraph Company, where he remained until 1934. From that year until his death he was with the Bell Telephone Laboratories, Inc. , first as transmission theory engineer, then as research mathematician. Carson's entry into the American Telephone and Telegraph Company in 1914 was timely, for the art of electric communications was about to receive a great impetus from a revolutionary new device, the high-vacuum thermionic amplifier or triode. Preparations were being made for the first field experiment in electronic radio telephony, the pioneering transoceanic tests of 1915, and Carson's assignment was on the theoretical side of this project. The remarkable properties of the triode challenged him to a mathematical analysis of it as a circuit element, especially as a modulator, an analysis which revealed the components of carrier and two side bands. A colleague was finding experimentally that reception of a modulated wave could be enhanced by inserting in the detector additional carrier energy of identical frequency the Homodyne method of reception. Carson recognized that since the carrier can be reintroduced in the receiver it need not be transmitted in the first place, thus saving power; also that one of the two side bands could be filtered out at the sending end, saving channel space. Thus was born the single-side-band, carrier-suppressed method of high-frequency transmission, Carson's greatest invention, which has come into general use (U. S. patent No. 1448382, filed 1915). When radio broadcasting started in the early 1920's, the frequency space allottable to it was so limited that engineers sought to narrow the band width of the emission, and there was advanced the scheme of modulating the frequency of the carrier instead of the amplitude. Carson in 1922 examined this proposal and showed it to be fallacious, demonstrating that the band width could be no narrower, and was likely to be much wider, than for amplitude modulation. Later, in the 1930's, radio evolved to much higher frequencies, as a result of which frequency modulation tended naturally to occur, and there was now frequency space enough to permit this being done. "F. M. " was found to be advantageous in overcoming interfering noises if a wide frequency swing and an amplitude limiter in the receiver the invention of Edwin H. Armstrong, who had long been working on the problem of frequency modulation were used, and as a consequence F. M. transmission came into commercial use. Carson and a colleague, T. C. Fry, published in 1937 the fundamental equations of F. M. applied to noise discrimination. About 1920 Carson initiated a continuing study of the mathematical theory of electromagnetic wave propagation over wires and through space. It branched out in many directions, as in proximity effect in parallel wires, radiation from transmission lines, and ground return impedance. A paper on wire transmission theory which formulated the approximations underlying the usual steady-state engineering equations was presented by Carson at the International Congress of Telephony and Telegraphy at Como, Italy, in 1927. For his new approach to such problems he received a citation from the Telephone International Consultative Committee at Prague in 1931. In 1936 Carson played the leading role in preparing, with two collaborators, one of two pioneering papers on the Southworth hyper-frequency wave guide, the one on mathematical theory. In Oliver Heaviside's operational calculus Carson had found the rudiment of a powerful method of analysis not generally appreciated nor developed, and he placed it upon a logical and rigorous basis in advancing the theory of transient oscillations in lines and networks. This, perhaps his greatest scientific contribution, was presented in a series of lectures at the Moore School of Engineering, University of Pennsylvania, in 1925, and published in his book Electrical Circuit Theory and the Operational Calculus (1926). Altogether, some fifty scientific papers, marked by masterly exposition, and twenty-five United States patents evidence Carson's profundity and creativeness.
During their later life the Carsons lived in New Hope, Pennsylvania, and it was there that Carson succumbed to a coronary thrombosis in 1940. Following cremation, his ashes were scattered on the Delaware River.