I think the issue at UBI is one of the upconverters or modulators. The HPA is putting up two carriers in the transponder. If BOTH were going up and down equally it would be the AMP.<br /><br />But since the uppwer and lower carriers are unbalancing, it has to be either the upconverter or modulator as the outputs of the upconverters are then combined through a 15 GHz combiner and fed to the HPA.