Abstract: Means and method for producing, at a plurality locally spaced of transmitting stations, an audio frequency pilot signal to be fed by the stations into a common communication or power transmission network, the pilot signals fed by the stations being synchronous and in phase with one another. The pilot signals are synchronized by a subharmonic frequency signal generated at a central station by frequency division and fed to each of the transmitting stations. At each transmitting station, a phase-locked-loop circuit is employed to set and maintain the pilot signals in phase with the subharmonic frequency signal.