Separating and Timing Overlapping Sofar Signals

Abstract

In multiple solar signaling over long distances, where the solar wavetrain is a few seconds in duration, the problem of a large signal obscuring the cutoff of another smaller signal may occur. This paper describes a method of separating the two signals for timing purposes. The frequency spectrum of an underwater explosion signal displays a line structure caused by interference between the shock wave and the first bubble pulse. At 32, 52, 72,⋯, of the bubble-pulse frequency, the shock wave and first bubble-pulse wave are 180° out of phase and sharp nulls in the explosion frequency spectrum result. Since the bubble-pulse frequency is determined by the size and depth of the explosion, two sofar depth charges of different weights will produce signals with different null frequencies. By passing the overlapping signals through a narrow bandpass filter set at the null frequency of the larger signal, the smaller obscured signal will be enhanced as much as 12 dB, relative to the larger signal and the obscured sofar cutoff may be timed with an accuracy of 50 msec.