Alexander Stepanovich Popov (16.03.1859 — 13.01.1906) — Russian physicist and electrical engineer, inventor of radio. Born in the settlement of Turyinskiye Rudniki (now the town of Krasnoturyinsk, Sverdlovsk Oblast). Graduated from St Petersburg University (1882). In 1883-1901 he taught at military institutions in Kronstadt. From 1901 — professor at the St Petersburg Electrotechnical Institute (from 1905 — rector).
His research concerned various problems of electrical engineering and radio engineering, in particular radio communication. In 1888 he repeated H. Hertz's experiments on producing electromagnetic waves, and in 1889 was the first to point out the possibility of using them to transmit signals over a distance. In 1894 he constructed a generator of electromagnetic oscillations and a coherer — an element of a receiver sensitive to electromagnetic waves. In the same year he invented the first receiving antenna and established that its receiver responds to lightning discharges. He created an instrument for registering discharges at considerable distances — the so-called lightning detector, which was the prototype of the first radio receiving station. On 7 May 1895 he demonstrated his lightning detector (radio receiver) at a meeting of the physics section of the Russian Physico-Chemical Society and read a paper, “On the Relation of Metallic Powders to Electric Oscillations”; there he also expressed the idea that his lightning detector could be used to transmit signals over a distance. On 24 March 1896, at a meeting of the physics section of the Russian Physico-Chemical Society, he demonstrated with his instruments the transmission of signals over a distance of 250 m, sending the world's first radiogram, consisting of two words — “Heinrich Hertz”. Somewhat later G. Marconi built similar instruments and carried out experiments with them.
In 1897 he was the first to detect the phenomenon of the reflection of waves from objects (in particular, ships) lying in the path of their propagation. This phenomenon was taken as the basis of radar. He carried out a series of experiments in radiotelegraphy over considerable distances.
To perpetuate Popov's memory, the Presidium of the USSR Academy of Sciences established in 1945 the A. S. Popov Gold Medal for outstanding achievements in radiophysics. 7 May became Radio Day.