Simultaneous transmission of TV and sound channels through a satellite transponder - An investigation of intermodulation

The proposed Australian National Satellite System, intended to provide TV and radio transmission to remote areas of Australia, requires that television and radio services be combined through the same transponder. A single-channel-per-carrier (SCPC) system is being considered for this purpose, but intermodulation may degrade the performance. A simulation satellite transponder and SCPC system has been designed to measure intermodulation and to assess its effects. The optimum transponder operating point for minimizing the effects of intermodulation is shown, and the associated disadvantage is quantified as the amount by which the carrier to thermal noise ratio must be increased to obtain an equivalent picture quality when the SCPC system is used in the transmission. The two proposed means of transmission (direct broadcasting and relay to local transmitters) are compared. The direct broadcasting method is less advantageous as it operates closer to the FM threshold. In addition, it was shown that full performance for the sound system can be obtained.