For signal injection in time-multiplex systems operating on the ‘resonant transfer’ principle two methods are described. In 2-wire systems the injection is accomplished by means of a pulse circuit similar to that of the subscriber but without a low-pass filter. For charging the injector-circuit capacitor in the pause between pulse positions a specially designed signal generator is connected to the circuit by means of a time-controlled pulse contact. The capacitor is always charged to the instantaneous voltage of the signal generator independent of chance residual charges, which may otherwise cause crosstalk.In 4-wire systems a simplified procedure may be adopted. The functions of charging contact and injector contact are here combined in a single pulse contact, which connects the signal generator directly to the receiving highway. This pulse contact closes coincidentally with the subscriber contact, but breaks earlier. Under specific conditions the following functions are obtained: current zero or minimum at the instant when each contact breaks. Voltage maximum on the subscriber capacitor at the instant when the subscriber contact breaks while simultaneously a voltage minimum on the highway tuning capacitance nears zero. Finally some methods for generating sinusoidal or composite signals are described.