. QST . ic core is the temperaturecoefficient of the core material. Because of thelow Curie point (the temperature at which thepermeability becomes practically unity) of Fer-roxcube materials, the permeability of the mate-rial is ciuite temperature-sensitive. Since the in-ductance varies directly with the permeability,its temperature coefficient will be identical withthat of the core. This temperature coefficient canbe inadmissably high for coils used in narrow-band sharply-tuned filters. The influence of thecore material on the inductance must be de- ■* Manufactured by Ferroxcube Corporation
. QST . ic core is the temperaturecoefficient of the core material. Because of thelow Curie point (the temperature at which thepermeability becomes practically unity) of Fer-roxcube materials, the permeability of the mate-rial is ciuite temperature-sensitive. Since the in-ductance varies directly with the permeability,its temperature coefficient will be identical withthat of the core. This temperature coefficient canbe inadmissably high for coils used in narrow-band sharply-tuned filters. The influence of thecore material on the inductance must be de- ■* Manufactured by Ferroxcube Corporation of America,and Philips Industries, Eindhoven. Obtainable in Canadathrough Rodgers Majestic; in Great Britain through Mill-iard Components Division, and in the U. S. A. throii^h FerroxcuVii- Ci,r\ 97 Marslmll St., North Avlams, Mass. Ferroxcube pot cores make itpossible to build high-(? inductorsfor super-selective ampli-fiers. The component parts and acomplete assembly are shownhere. April 1955. creased, and this is achieved liy providing an airgap. In general, there is an optimum air-gap sizefor a given Q. In some cases, especially at lowfrequencies, it is desirable to choose an air gaplarger than optimum for a given Q, in order toincrease the stability of the coil. A larger air gapalso reduces premagnetization effects. Therefore,the largest air gap for the given Q should alwaysbe used. As a general Iule, the higher the fre-quency the greater the optimum size of the gaps larger than mm. the core should besymmetrically located, leaving half the total tapat each end. For frequencies less than about 30 kc. the bestQ is obtained by winding the coil with solidenamel-covered wire (not silk-covered), with the I I TJ (A) (B) T^^ (C)
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
