In the present paper the self capacity of coils for radio use was studied systematically from both experimental and theoretical sides. Coil specimens under test, all wound on glass hollow cylinders with double cotton covered copper wires, included seventeen different coil of each type, single layer, two-layer, three-layer and four-layer banked windings, forming a total o sixty eight. Measurements of the self capacity and ilie natural resonant wave length of the coil were carried out when both ends of the coil were icsolated from the earth. The diameier of coils varied from about 6 to 22 c.m. and the axial length from 2, 5 to 20 c.m.

Part I is the brief description of literatures on this field of study.

Part II concerns with the preparation of coil specimens and the methcd of experiments. (Tables 1, 2, 3, 4 are to be refered)

Part III shows the experimental results. Since the radius of the coil r is the most important factor in determining the self capacity of the coil C0, the rat o C0/r was taken as a function of the dimension ratio h/2r. Curves (1) (2) (3) (4) show the ratios C0/r and λ0/2l as functions of h/2r.

From these results it was found that the ratio C0/r of the single layer coil remains practically the same for dimention ratios greater than unity, say 0.6, in our case. And although the value of C0/r of multi-layer banked winding coil is in general greater than that of the single layer coil having the same dimension ratio, this difference in self capacity practically disappears when the dimension ratio is greater than 2. That the ratio C0/r increases rapidly with small dimension ratios is die to the effect of glass frames.

The ratios of the fundamental natural wave length to their higher natural ones of the coil were investigatd and it was found that they take the normal harmonic order when the dimension ratio lies between O.5 and 0.7 (Curves (1°) (2) (3°) (4°) are to be refered.)

Part IV shows the value of C0/r calculated by the methed of Prof. Howe (Curve (B) is to be refered). These values agree with our experiments.

Part V shows the values of C0/r deduced from Drude's experimental results on natural resonant wave length of coils (Curve (C) is to be refered). It was shown that these values are greater than these calculated by Howe's method by 24% (March, 1924)

Part I Introduction.

Part II Preparation of Coil Specimens and the Method of Experiments.

Part III Experimental Results.

Part IV Calculation of Self Capacity By Howe's Method.

Part V Self Capacity Deduced From Drude's Experimental Results.

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The Institute of Electrical Engineers of Japan