Open-Wire Crosstalk

T HE tendency of communication circuits to crosstalk from one to another was greatly increased by the advent of telephone repeaters and carrier current methods. Telephone repeaters multiplied circuit lengths many times, increased the power applied to the wires, and at the same time made the circuits much more efficient in transmitting crosstalk currents as well as the wanted currents. Carrier current methods added higher ranges of frequency with consequently increased crosstalk coupling. Program transmission service added to the difficulties since circuits for transmitting programs to broadcasting stations must accommodate frequency and volume ranges greater than those required for message telephone circuits. As these new types of circuits were developed, their application to existing open-wire lines was attended with considerable difficulty from the crosstalk standpoint. Severe restrictions had to be placed on the allocation of pairs of wires for different services in order to keep the crosstalk within tolerable bounds. In many cases the existing lines were retransposed but, nevertheless, there were still important restrictions. While great reduction in crosstalk was obtained by the transposition arrangements the crosstalk reduction was finally limited by unavoidable irregularities in the spacing of the transposition poles and in the spacing of the wires, including differences in wire sag. To further improve matters it was, therefore, necessary to alter the wire configurations so as to reduce the coupling per unit length between the various circuits.