Electro-pneumatic air modulator for fog signals

This paper describes a highly-directional electropneumatic loudspeaker system capable of radiating any type of warning signal in the 100-1000 cps range as well as speech. The mechanism of the electropneumatic device is described in detail. Field measurement data on the directional characteristics, maximum range, and the effect of wind, which we gathered on tests performed at Point Montara, Calif., are presented. Aspects of signal duration, threshold, and new requirements for fog signal resulting from new trends in coastal shipping patterns, as for example, the increase in private craft, are discussed.