Electrical news and engineering . ter of wires in inches. k equals specific inductive capacity of dielectric betweenconductors (for air equals 1).1 equals length in miles. The only other point to be considered is the apparentresistance of the coils at different frequencies. An thesecoils are manufactured under patent very little reliable in-formation is to be had regarding their characteristics. Butit may be taken as correct that these coils are wound uponrings of magnetic material and have, practically speaking,no external field. Consequently they can be encased inmetal and providing there is
Electrical news and engineering . ter of wires in inches. k equals specific inductive capacity of dielectric betweenconductors (for air equals 1).1 equals length in miles. The only other point to be considered is the apparentresistance of the coils at different frequencies. An thesecoils are manufactured under patent very little reliable in-formation is to be had regarding their characteristics. Butit may be taken as correct that these coils are wound uponrings of magnetic material and have, practically speaking,no external field. Consequently they can be encased inmetal and providing there is a thin iron shielding plate be-tween them to provide against electrostatic and electromag-netic action may be packed on top of one another withoutany fear of induction between themselves or from otheroutside sources. The best magnetic cored coils have a time constant ofabout (L/Rc) at 800 cycles per second, so that Lbeing known the apparent resistance can be calculated. Summarizing the above results it has been shown that. iio matter lunv heavily a circuit may be loaded it is impos-sible to make it distortionless for all periodicities requiredin telephonic speech. This being the case the circuit willgive the best efficiency when it is loaded just sufficientlylo give the required transmission for the ultimate distancefor which it is designed; to get this result if d equals this<listance in miles, theoretically B should equal )U/d butin practice this value of B has to be reduced approximately10 per cent, to allow for extraordinary losses, such as leak-age, eddy currents, and hysteresis losses, which exist onthe circuit but which caiimii In- calculated. This value for TII K ELECTRICAL NEWS 61 H approximately very closely to the values calculated fur thelimiting distance of sjieech for metallic circuits of variousKauges. lrom equation (1) or (2) for li, the required value olH being known, L can be calculated. Phc values of L. C, and R (resistance of mile of cir-cuit
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