Abstract: A coherency generator for providing signals to control the time and phase coherency of data information signals in an overlap region of a simulcast system that comprises a control site and a plurality of remote broadcast sites. A channel card located at each remote site derives from the information signals a master clock signal for synchronizing the broadcast of data information on an RF carrier. At substantially regular intervals a transmit section of the coherency generator transmits a synchronization command signal after detecting a predetermined sequence of ones or zeros. A receive section of the coherency generator issues a reset pulse to the remote site channel card upon detecting a predetermined pattern of values of a preselected data bit, and following detection of the synchronization command pulse. The reset pulse clears the memory elements of the channel card, setting the phase of the clock signal.

Abstract: A simultaneous broadcast (simulcast) system transmits from a control site to two or more remote sites the same data information along with a synchronous digital signal via a synchronous digital transmission network. At the remote sites, a clock signal is derived from the digital signal for timing the broadcast of the data information on an RF carrier. The clock signal phase is periodically reset to a known phase using a predetermined pattern of data bits in the digital signal. A time delay circuit at the control site delays the synchronous digital signal such that, where RF carrier signals from the remote sites overlap, there is time coherency between the data information. The time delay circuit is constructed so as to preserve the synchronization of the digital signal.