A System of Delayed Feedback Applied to Sonar

Abstract

An equipment for improving the signal to noise ratio of a sonar has been designed based on the delayed feedback theory. Because the delayed feedback circuit for the sonar needs the delay element with greater delay time in relation with the velocity of sound, the authors used the magnetic recorder as the delay element and applied the frequency modulation method to get rid of the wave from distortion. To make the delay time equal to the repetition period of the sonar pulse, the magnetic recorder utilizes two tracks, one of which carries the signal to be delayed and the other carries a synchronization pulse. Since the period of the synchronization pulse is equal to delay time of the signal, this pulse is fed to the sonar and synchronizes the generation period of the transmitting pulse. The results of the experiment are as follows: Using rectangular pulse as the echo, the degree of the signal to noise ratio improvement coincided fairly well with 1/1-α which was derived by the theory. On the other hand using the real sonar echo pulse, the photograph showed that this system enhanced the echo signal in the existing noise. Therefore, these results show that this system is effective for the increase of the sonar detecting performance.