The intermodulation due to the traveling-wave tube (THFT) is analwed for the case where arbitrarily modulated carriers and Gaussian noise are amplified through the TWT. Both AM-PM conversion effects and nonlinear amplification in the TWT are considered. The-possibility of reducing intermodulation for system improvement is also discussed.

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Absrrucr-An investigation of ways to improve the capacity in a dedicated SCPC transponder has resulted in the development of a method for optimizing the transponder capacity and link performance in preassigned multilevel SCPC systems.The main approach is to form different groups of carriers based on the traffrc requirement, and on typical characteristics of the link destinations such as variations ,in the satellite e.i.r.p. and downlink path loss, and differences in the receive earth station antenna size. The Fletcher-Powell optimization technique is used to determine the set of optimum carrier levels at the transponder TWTA input.Application of the method to a number of preassigned multilevel frequency plans in a global transponder environment clearly indicates that the total carrier-to-noise ratios for all the links can be optimized at any specified CNR value, and that the optimized capacities are substantially higher than that of the basic two-level system. The implementation of multilevel plans is fairly simple if all downlink carrier levels can be monitored at some reference station in the SCPC network to reasonably control the uplink e.i.r.p. levels.

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