. Robison's Manual of radio telegraphy and telephony for the use of naval electricians . Fig. 73.—Helix and Spark Gap. 134 MANUAL OF RADIO TELEGRAPHY AND TELEPHONY. srariable connection to the helix so that the wave length can be varied.(Figs. 42 and 43.) It must not be forgotten that varying the wave length of eithercircuit by varying the inductance of the coupling coil or coils varies themutual induction, as well as the self-induction, and also the couplingand damping, so that the most recent sets—Fessenden (fig. 45), Tele-funken (fig. 46), Lowenstein (fig. 47)—make provision for varying the
. Robison's Manual of radio telegraphy and telephony for the use of naval electricians . Fig. 73.—Helix and Spark Gap. 134 MANUAL OF RADIO TELEGRAPHY AND TELEPHONY. srariable connection to the helix so that the wave length can be varied.(Figs. 42 and 43.) It must not be forgotten that varying the wave length of eithercircuit by varying the inductance of the coupling coil or coils varies themutual induction, as well as the self-induction, and also the couplingand damping, so that the most recent sets—Fessenden (fig. 45), Tele-funken (fig. 46), Lowenstein (fig. 47)—make provision for varying thewave length at some other part of the circuit than at the coupling coil,or, as in the Lowenstein sets, for automatically moving the coils so as tomaintain the same coupling when the wave length is varied. These out-side coils are called loading coils, as distinguished from the coupling. Fig. 74 Wave changer. coils, by means of which energy is transferred from the closed to theopen circuit (and vice versa in sets not having quenched or properly air-cooled gaps). The method of building the Telefunken variometer coils, shown infig. 46, is illustrated further in fig. 74. This method of varying theself-induction of a circuit has the advantage of not having any dead endsas in the old inductance helices, shown in fig. 73. However, the vari-ometer shown in fig. 74 is not suitable for inductive coupling. The spiral inductance, shown in fig. 72, is suitable for both direct andinductive coupling, and also for loading coils. It is convenient to manu-facture and to mount and is coming into use rapidly. The inductanceshown in fig. 72 is an early DeForest type. MANUAL OF RADIO TELEGRAPHY AND TELEPHONY, 135 The common method of shifting wave lengths quickly is hy means of thenavy standard wave changer. A simple wave changer is shown in Fig. coils of the primary and secondary
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