In the presence of a priori data on the carrier frequency of the signal, its shape and modulation parameters, selective amplifiers can be developed using well-known methods which are based on the use of modulated second-order filters. It is difficult to obtain a priori information which would be sufficient to enable these methods to be used, and because of this we have to develop selective systems using a smaller amount of a priori data. Shortage of a priori data on the signal also gives rise to difficulties when signals of a given form are simultaneously amplified and generated. The design of amplifier-generators involves the use of methods which differ from those which are used in the development of selective amplifiers. Despite the fact that these amplifiers differ, they can be synthesized using a single method. The method of synthesizing selective amplifiers and amplifier-generators that are invariant with respect to a shortage of a priori information on the parameters of the signal (parametrically invariant amplifiers) consists of synthesizing algorithms of the operation of amplifiers and their circuit realization.
