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We describe here a simple method to synchronize three TV signals originated from noncolocated up-link stations in a satellite Time-Compression Multiplexing (TCM) system. In this system, information in three fields of each TV picture is compressed into a single field time so that the compressed signals from the three sources can be time multiplexed for transmission. The up-link synchronization ensures that the Radio Frequency (RF) bursts from different sources will arrive at the satellite without collision. Our method employs a dynamic master/slave arrangement whereby the first station signing on assumes the role of a master. The other stations subsequently can synchronize their transmissions to the master's by simply monitoring the received RF bursts from the satellite, measuring their respective delays to the spacecraft, and then phase locking their local color subcarrier clocks to the master's transmitted bursts. When the master station stops transmitting, an automatic procedure is provided for the second station to take over as the new master. The worst-case jitter performance is well below 100 ns, and the initial acquisition time can be kept less than one-half second. These are more than adequate for the present TV application, although further improvements are possible if necessary. |
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