. The Bell System technical journal . h that theoretically there is nomagnetic coupling between the two circuits for longitudinal currents ineither one, regardless of the coil setting. Unless the capacitance be-tween primary and secondary windings can be kept very small, theresultant admittance unbalance produces crosstalk which is not com- CROSSTALK AND NOISE FEATURES 149 pletely balanced out when the coil is adjusted. The turns of conductorin the Fig. 5 coil are so located that this side-to-side capacitance un-balance is less than 5 micro-microfarads. The capacitances betweenwires of either
. The Bell System technical journal . h that theoretically there is nomagnetic coupling between the two circuits for longitudinal currents ineither one, regardless of the coil setting. Unless the capacitance be-tween primary and secondary windings can be kept very small, theresultant admittance unbalance produces crosstalk which is not com- CROSSTALK AND NOISE FEATURES 149 pletely balanced out when the coil is adjusted. The turns of conductorin the Fig. 5 coil are so located that this side-to-side capacitance un-balance is less than 5 micro-microfarads. The capacitances betweenwires of either the primary or secondary winding do not affect theunbalance but contribute a part of the capacitance loading whichcompensates for the line inductance of the coils. In the actual balancing coil, shown in Fig. 6, the windings are locatedin channels cut in a fibre tube which is secured to a head carrying thewinding terminals and a bushing through which passes the threadedbrass rod supporting the two cores. Below the head are small spool. Fig. 7—Arrangement of inner winding of trial balancing coil. forms on which the shunts are wound. Insulating material such asbakelite is used to obtain proper spacing of the two cores. The rather unusual manner in which the turns are applied is illus-trated in Fig. 7, which is a closeup view of the two wires forming theinner winding. These two wires alternately cross over each other,progressing along the axis in opposite directions of rotation. Theouter winding is similarly applied. This type of winding eliminatesall splices within the coil, removing hazards incident to interior splices. The complete coil assembly is enclosed by an aluminum containerwhich serves the dual purpose of a shield and a convenient means ofholding the coil for mounting purposes as this container fits snugly into ISO BELL SYSTEM TECHNICAL JOURNAL an aluminum cup riveted to the assembly panel. The windings aredried and impregnated and the space between the coil assembly a
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