Page:Popular Science Monthly Volume 92.djvu/651

 Wireless Work in Wartime

IX. — The Primary Oscillation Circuits of the Spark-gap Transmitter

]5y John V. L. Hogaii

��THE March article of this series discussed the power-supply circuits of the spark-type radio transmitter, showing how alternating current energy was supplied to the power transformer and converted to a higher voltage suitable for charging the primary condenser. The illustration Fig. 34 is reproduced this month so that the details of this assembly

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����Fig. 32: The coupled two-circuit transmitter overcomes difficulties from the plain antenna

of apparatus may be held clearly in mind, and Fig. 32 is also shown again since it gives the normal connections from the primary condenser C to the spark-gap S and the several tuning coils. This in- stalment will take up the behavior of the spark-gap and the primary oscillation circuit, which is composed of the gap G, the condenser C and the primary Li of the oscillation transformer or inductive coupler.

In the first place, it must be understood that the transmitter really has two pri- mary circuits and two secondary circuits, just as it has two transformers. With reference to the low^ or audio frequency power-supply, (which is usually of from 60 to 500 cycles per second frequency), the primary circuit comprises the genera- tor armature, the key and the primary of the power transformer. The audio fre- quency secondary circuit involves the power transformer secondary S, and the condenser, C. In regard to the radio frequency oscillations which are produced by the condenser (and which in turn pro- duce the wireless waves), the other pri-

��mary circuit consists of the condenser C, the spark-gap G, and the primary coil Li of the oscillation transformer or inductive coupler. The radio frequency secondary is formed of the antenna A, the antenna loading coil L3, the secondary L2, of the inductive coupler, and the ground connection E.

The Voltage Applied to the Condenser

Considering Fig. 34 for a moment, it should be evident that if an alternating current of 500 cycles (complete reversals) per second is developed by the generator, corresponding voltages will be applied to rhe plates of the condenser C. At inter- vals of 1/TOOO second this condenser will be charged in alternate directions, first with the upper plate positive and the lower negative, then with the upper plate negative and the lower positive. If the v.dres X and Y are left open or disconnected, the condenser charges wull merely flow back through the secondary winding S as the potential changes at each half cycle. The il- lustration Fig. 35 should make this action even more clear, since it shows the potential of the upper plate of the con-

���Fig. 34: In addition to the generator itself the circuits of the transmitter are shown

denser (with respect to the lower plate), at the various instants in a full cycle of 1 500 second. The wavy line repre- sents the passage of time by its progress toward the right (thousandths of one second are marked off along the hori- zontal line or axis of time) and the poten- tial of the condenser by its vertical height

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