1. The method of communicating from a first station to a second station over a dispersive transmission link, comprising the steps of: (a) transmitting from the second station an interrogation signal of such bandwidth that it is distorted upon arrival at the first station, (b) receiving said distorted signal at the first station, (c) producing a signal that is substantially a replica of the received distorted signal but reversed in time sequence, (d) delay modulating said replica signal by intelligence to be communicated from said first station to said second station to produce components each identical to said replica signal but amplified, phase shifted and delayed with respect thereto by amounts equal to, respectively, the amplitude, phase and time position of the element of said intelligence that it represents, (e) transmitting said delay modulated signal from said first station to said second station over the same dispersive transmission link as said interrogation signal, whereby each component of said modulated signal undergoes the same distortions in traveling from the first station to the second as said interrogation signal does in traveling from said second station to said first station and the sum of said redistorted components received at said second station is intelligible representation of said modulating intelligence.