Coupling capacitors for carrier current applications

Coupling to high-voltage transmission lines for purposes of carrier-current communication was first universally made by means of coupling wires. This type of coupling usually required high-power transmitting equipment, but when coupling capacitors were substituted it was possible to reduce the carrier input to the line without affecting the received signal strength. The paper gives an approximate method for determining the effectiveness of coupling wires and coupling capacitors. No attempt is made at refinements in calculations as it is only desired to show the effect of stray capacity. Curves show the change in practise from coupling wires to coupling capacitors. It is estimated that by the early part of 1928 the total number of the two types of coupling will be equal. The electrical characteristics for different types of insulation used in coupling capacitors, based on test results is given. Some important points of design for the new cable capacitor are included.