For communications satellites carrying a phase-shift keying (PSK) modulated carrier in one transponder and FM carriers in neighboring transponders, there is a potential adjacent interference effect from the PSK carrier into the FM carriers. In this correspondence the noise-power ratio (NPR) degradation is calculated for the top voice channels of the FM carriers as a function of the time-division multiple-access (TDMA) transponder single-carrier saturated equivalent isotropic radiated power (eirp), the TDMA transponder output filter selectivity, and the FM carrier sizes, Calculations are performed for the specific parameters of the INTELSAT IV system and compared with laboratory measurements. However the results are easily extendable to other communications satellite systems.

An efficient multiplexing approach that achieves good intermodulation distortion performance by effectively trading off modulation power improvement is described. Emphasis is on practical application to aircraft communications systems via a relay satellite.