Nyquist 1 universal filters

The Nyquist (1928) 1 filters (NFls) with both nonlinear phase response and amplitude response of nonspecified symmetry are investigated. It is shown that one of the filter's responses (amplitude or phase) can be chosen almost arbitrary. The second one is then derived from the condition of zero intersymbol interference (ISI) in data transmission synchronous systems. As a specific application of the presented theory, a simple procedure for calculating NFl's with ISI-free matched and unmatched filter properties is proposed.