WIRELESS TELEPHONY

Waipa Post, Volume 43, Issue 3354, 29 September 1931, Page 6

WIRELESS TELEPHONY

ITS PROGRESS TRACED. The problems of the scientists and of the inventor are often of such a delicate and complex nature as to be quite beyond the grasp of the average person. After the problem of wireless telegraphy had been solved, for example, the would be likely to jump to the conclusion that the problem of wireless telephony would quickly be solved. Yet this was by no means the case. Indeed, the problem of wireless telephony was not completely solved until comparatively recently. An almost incredible amount of .experimentation and research has been devoted to this problem, in order to make the invention commercially practicable. Graham Bell .gave no.little thought to the matter, and invented the instrument known as the photophone. But this instrument was so limited in range as to be impracticable as a commercial system. . It is quite true that.the principles of wireless telephony are modifications of those of wireless telegraphy. But the difficulties to be. surmounted in .wireless telephony were incomparably greater. A means to be found for propagating continuous electric waves at radio frequency. An electric arc consists of two carbon rods close together and.connected to • a source of electrical current. By connecting an arc: with a direct-cur-rent dynamo on the one hand and with a condenser on the other, the latter becomes charged and discharged, thus alternately lowering and increasing the current through the arc. If the frequency of this ebband flow of the current does not exceed 30,000 cycles a second, the arc gives "off a musical note, the pitch depending on the frequency. Because of this fact, this type of arc has been called the singing or musical arc. Wireless telephony became a practical proposition when William Duddell in 1900 discovered that the singing arc emitted continuous oscillations of constant, amplitude. Unfortunately, a high frequency 100 times as great als that provided by the singing arc was needed for satisfactory transmissions. In 1903 Valdemar Poulsen of Cop-

enhageh improved the arc considerably; and succeeded in transmitting speech from Berlin to Copenhagen, a distance of some 290 miles. Somewhat later Dr J. Vanni hit upon the ingenious; invention of a liquid microphone. With this new invention, Vanni succeeded in transmitting speech from Rome to Tripoli, a distance of some 600 miles. Dr Goldschmidt invented the ingenious ro-tating-frequency; alternator, in which a low-frequency current is transformed so that its frequency is increased as desired. One of the earliest long-distance stations to use the Goldschmidt alternator for transat-

- / lantic service was the one at Hanv.;oyer,» Germany, working direct with ' vTuckerton, New Jersey." Another -,; type of alternator was invented by E. F. W. Alexanderson of the Inter-

national General Electric Co. Huge -machines of this type haye been in- .. stalled at many stations' in this cdunv*?y and ; , of- -the ';■': thermibnic valve ,• finally . . "brought wireless telephony to its pre- . sent stage of effective operation. '-:.■/.