Automatic clear voice and land-line backup alignment for simulcast system

Abstract

In a multiple site radio frequency (RF) simuicasting transmission system, voice and digital data distributed via multi-phase modem over 'land-line' inter-site communication links from a control point to the RF transmitter sites exhibit random time delay skew because the modems at each site recover clock signals from an arbitrary one of multiple phases. Reference 'tones' for data alignment, consisting of a high frequency clocking signal and a low frequency 'gating' signal, are generated at each site synchronized to a GPS broadcast reference signal. Similar tones are also provided to transmitter sites along with the distributed data via the land-line inter-site communication links as a backup. The pair of 'backup' reference tones supplied via land-line are automatically aligned at each site to the GPS receiver generated reference tones by individual phase comparison and dynamically-adjusting delay circuits. Consequently, sites can compensate for any land-line path re-routing--so long as the GPS system is operational. In the event of GPS receiver failure or loss of GPS signal lock a delay adjustment inhibit feature is provided to preserve the most recent and accurate delay setting. A site switches over to the land-line backup reference tones once a maximum 'free-running' tolerance time limit for the GPS receiver reference tone generator has been exceeded. In an alternate embodiment, backup reference tone phase comparison is coupled with a circuit for adjustably delaying a composite inter-site link T1-type channel signal. This arrangement automatically aligns the backup reference tones to match analog voice data ('clear voice') signal path latency.