. La télégraphie sans fil pratique; un livre de texte complet pour les étudiants de la communication radio . eign radio system, l'élément d'inductance connu sous le nom de variometerintronance est employé pour changer la dégree de couplage entre les circuits fermés et ouverts de la radio-fréquence. Brièvement, il se compose des enroulements A et B, Fig.123, comprenant deux bobines qui peuvent bimagnétiquement s'opposer l'une à l'autre. Les huiles de ce type sont connectées en série et lorsque l'inductance est légèrement opposée à l'inductance à une valeur mini-MOM, mais lorsque B est tiré à partir DE A, l'inductance augmente graduellement,l'inductance maximale est obtenue lorsqu'elles sont ar
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. Practical wireless telegraphy; a complete text book for students of radio communication . eign radio system, aninductance element known as a variometerinductance is employed to change the de-gree of coupling between the closed andopen circuits of radio-frequency. Briefly, it consists of the windings A and B, Fig.123, comprising two coils which can bemagnetically opposed to each other. Thecoils are connected in series and when di-rectly opposite the inductance is at a mini-mum value, but when B is drawn awayfrom A the inductance gradually increases, maximum inductance being obtained whenthey are drawn completely apart. If the variometer is connected in theaerial system as in Fig. 124, and its self-inductance gradually increased, the mutualinduction between the open and closedcircuits will be increased and therefore thecoupling. To be efficient and to have a minimum resistance, variometers must be wound withstranded copper cable made of a great number of small strands each of which is insulatedfrom neighboring ones. A stranded cable made in this way is called Litzendraht which. Fig. 123- -Showing Fundamental Principle of the Vario-meter. APPLIANCES FOR A RADIO TRANSMITTER. 109 affords a conductor at maximum con-ductivity for high frequency currents.Oscillation transformers may havefixed values of inductance for both theprimary and secondary windings as inFig. 12S. In one type, the primary hasa single turn of copper cable woundaround 6 or 8 turns of smaller cable, constituting the secondary winding.The coupling is rather loose—about 8per cent, for the average aerial. Thenecessary changes of wave length areobtained by variation of the capacity ofthe condenser in the closed circuit andthe inductance of the aerial circuit. 104. Aerial Tuning Inductance. —The aerial inductance coil may beof the continuously variable typehaving a sliding contact whichbears on an edgewise copper stripas in Fig. 126, or of the round barrel type made of stranded copper cable
