The research on transmission and filter operations has two purposes. The first purpose is to reduce channel distortion and the second is to locate a source. It uses impulse responses of transmissions between a source and a receiver in a waveguide. A time reversal of the impulse response gives the matched filter for the transmission. The matched filter is an optimum filter for the reduction of transmission distortion. A numerical example demonstrates distortion reduction. Since the impulse response between a source and receiver is a function of waveguide structure, source position, and receiver position, one can use the impulse response to determine source position by passing the received signal through a set of reference or theoretical impulse response functions for trial source positions. The ambiguity of source locations depends on waveguide structure and the complexity of the impulse response. Basically ambiguity decreases as complexity increases. A plane‐layered waveguide requires at least three receivers that are not in a line. The signal processing consists of match filtering each receiver for a trial source location and then cross correlating the trial filter outputs. The pairwise cross correlations have a maximum when the trial location is the same as the source position. The cross correlation at match also gives an estimate of the autocorrelation of the source. The source can radiate impulsive transients or continuous random signals.