Effects of cable irregularities on the operation of telephone repeaters

Ideal conditions for voice frequency telephone repeater operation consist essentially of having line facilities with infinite ¿return loss.¿ In practice, these conditions cannot be achieved, nor need they be. All that is actually needed is an adequate degree of balance at all frequencies of interest between two circuit elements, such as a line and its balancing network, to permit deriving the required amount of repeater gain and still to have a 3 to 6 db (decibel) margin of gain before oscillation or ¿singing¿ occurs.