*U.S. Patent No. 2,390,847 , 12/11/1945 (app. 08/13/1941) [DjVu116KB]
SIGNAL TRANSLATING APPARATUS (class: 181/142; 333/32; 367/172; 367/174)
Olson, Harry F. (assignee: Radio Corporation of America)
Abstract: This invention relates to signal translating apparatus, and more particularly to a microphone which is especially useful in submarine signalling.