Multi-channel transponder with channel amplification at a common lower

Abstract

Input RF signals to a transponder, such as a communications satellite, are down converted to a lower intermediate frequency (IF) that is common for each different channel. The channel signals are all processed at the common IF, and then up converted to different respective transmission frequencies. This allows for a down conversion/signal processing/up conversion unit design that is the same for each channel (except for frequency and gain values), and facilitates the use of inexpensive available standard components as well as low bandwidth channel filters. An improved phase noise cancellation phase lock loop (PLL) is preferably used to generate tuning signals used in the up and down conversion processes. The PLL includes two loop mixers, with the down and up conversion mixing signals taken respectively from the inputs to the first and second loop mixers. The first and second loop mixers receive mixing signals at frequencies (T-R) and (T-IF-N.multidot.CLK) respectively, where T is the channel's transmission frequency, R is its reception frequency, N is the PLL's .div.N factor, and CLK is a clock frequency; the PLL's voltage controlled oscillator provides the down conversion tuning signal and the input to the first loop mixer at a frequency (R-IF), while a (T-IF) tuning signal for the up converter is taken from a filtered output of the first loop mixer.