. Practical wireless telegraphy; a complete text book for students of radio communication . e where the diameter is 9J/2 times the length This covers all conditionsencountered in practice. (c) Correction factor.—For practical calculation the foregoing formula is sufficientlyaccurate, but for greater precision a correction factor must be applied. In fact, the inductancevalues obtained in examples 1 and 2 are termed the current sheet inductance, based uponthe assumption of a coil wound with infinitely thin tape, the turns of which are assumed totouch but not to be in electrical contact. Dr. Rosa
. Practical wireless telegraphy; a complete text book for students of radio communication . e where the diameter is 9J/2 times the length This covers all conditionsencountered in practice. (c) Correction factor.—For practical calculation the foregoing formula is sufficientlyaccurate, but for greater precision a correction factor must be applied. In fact, the inductancevalues obtained in examples 1 and 2 are termed the current sheet inductance, based uponthe assumption of a coil wound with infinitely thin tape, the turns of which are assumed totouch but not to be in electrical contact. Dr. Rosa of the Bureau of Standards has given an expression for circular sectioned non-magnetic wire as follows: If the true inductance is designated as L, and the current sheetinductance as L-s, then, L = L-s — L-cwhere L-c is the correction value, and, L-c = 47r a n (&-f Ks)where Kz and Ka are constants of the coil. (See B. of S., vol. 8, pp. 197 and 199). dNow K> is a constant plotted to the parameter of — which is the ratio of the diameter 212 PRACTICAL WIRELESS TELEGRAPHY. lOO. ooo 010 ai5 oao oas ojs Fig. 232—Showing the Values of a Correction Factor for Determining the True Inductance of a Coil, PRACTICAL RADIO MEASUREMENTS. 213 dof bare wire to its pitch in a given winding and for any given value of — a value of Ka Dappears in Fig. 231. It should be noted that K2 may be positive, negative or zero; that is,on the left of the zero line lO is positive and on the right hand side negative. Ks is another factor plotted against the number of turns in the coil as in Fig. 232 whereit will be seen that Ka is zero for one turn and for 1,000 turns. (d) Corrections for Example 1.—We shall now calculate the value of L-c for example 1. dAssuming the wire of the helix to have a diameter of ^ inches with spacing of one inch, — .250 D :.02S and from the curve. Fig. 231, Ks = — (of negative value). Since N = 10, then from the curve. Fig. 232, Ka = , he
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