. Elements of radio telephony . n; thesevalues are essentially units of measurement and applicableequally well at any starting point. The frequency most commonly used on alternating-cur-rent power and lighting circuits is 60, and if the filamentsof the incandescent lamps could cool off rapidly enough theywould actually go out 120 times a second or every time thecurrent passed through zero. However the filament usuallystores up enough heat to supply it over the period of zerocurrent and we do not notice any appreciable flicker. In 6 HIGH-FBEQUMNCY CURRENTS 7 spite of the heat storage of the fil
. Elements of radio telephony . n; thesevalues are essentially units of measurement and applicableequally well at any starting point. The frequency most commonly used on alternating-cur-rent power and lighting circuits is 60, and if the filamentsof the incandescent lamps could cool off rapidly enough theywould actually go out 120 times a second or every time thecurrent passed through zero. However the filament usuallystores up enough heat to supply it over the period of zerocurrent and we do not notice any appreciable flicker. In 6 HIGH-FBEQUMNCY CURRENTS 7 spite of the heat storage of the filament, flickering is fre-quently noticeable on 15- and 25-cycle circuits. The frequencies used in radio work are very much higherthan those employed in power work. Radio frequenciesrange from about 15,000 cycles up to several millions ofcycles per second. Sound waves are alternating air currents or disturbancesin the air while radio waves are alternating disturbances inthe ether. Sound waves afei mechanical disturbances seconds. Fig. 3.—Alternating-current wave of 60 cycles frequency. while radio waves are electromagnetic disturbances. Lightand heat are electromagnetic ether disturbances similarto radio waves but of very much higher frequencies. Fig. 4has been drawn with the idea of comparing the varioussound and electromagnetic waves with which we have todeal. A piano keyboard comprises about seven frequencies of sound waves corresponding to notes oneoctave apart bear the relation to two to one. If we doublethe frequency of any given note we always get the octaveabore it. The drawing shows an enlarged keyboard withthe octaves indicated, it should be very definitely remem- 8 ELEMENTS OF RADIO TELEPHONY bered that although marked on the same scale, that there is afundamental difference between sound and radio, light, andheat waves other than that of difference in frequency. Aswe increase the frequency from the audible range of the pianowe reach the limit to which t
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradio, bookyear1922
