Radio broadcast .. (1922-30)

Making Life Safe at Sea 473 NANTUCKET SHOALS LIGHTSHIP B ^— --"PALTfC'S COURSE TO RF£CUE REPUBLIC ^•"" CHART MADE BY AN OFFICER ON THE S. S. " BALTIC Shows how the disabled Republic was finally located by means of submarine signals and illustrates how much more rapidly the rescue could have been effected had she been equipped with some sort of sub-sea signaling device place. An alternating current, vibrating at about one thousand cycles causes the steel diaphragm to vibrate, thus producing a shrill note, somewhat similar to the note produced in a radio receiver by a spark transmitter fed by a looo-cycle generator. Although the diaphragm of the oscillator is of steel about three-quarters of an inch thick, it was found that, used as a receiver, sounds could be received many miles when it was connected with vacuum tube amplifiers. In an address delivered August 30, 1920, Mr. Hammond V. Hayes, Chief Engineer of the Submarine Signal Company, said of this phase of the business, "Not only were such sounds audible in telephones, but phonograph records were made of them and, possibly even more remarkable, photographs of the sounds produced by invisible ships were taken." These under-water sounds are produced by the movements of propeller blades in the water and by ships' auxiliary machinery. Most ships, it was found, had their own distinguishing noises, and it became possible later for men expert in listening, not only to report the type of FESSENDEN OSCILLATOR Used for producing and receiving submarine signals. The note produced by this oscillator is quite similar to the 500-cycIe quenched spark radio transmitter METHOD OF INSTALLING The Fessenden oscillator on shipboard. Part of the vessel's skin is cut away and the hole is filled up by the front surface of the oscillator