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Dr. Louis Cohen who, while associated with the National Electric Signaling Co., had worked with Dr. Austin in the formulation of the Austin-Cohen empirical formula, had devised a new means of coupling, utilizing condensers in lieu of the induction coils used by Marconi. The Navy obtained the right to the use of the Cohen patents and procured his temporary services to assist in the design of receivers. [Annual Report of the Secretary of the Navy, 1915, (Washington Government Printing Office, 1915), p. 267.]
6. FIRST NAVY DESIGNED AND MANUFACTURED RECEIVERS
The Washington Navy Yard, responsible for design of receiving equipment, established a radio laboratory in the River Radio station, which had not been used since the establishment of the station at Radio (Arlington), Va. There, Cohen, assisted by Clark and L. G. Butte, took the best portions of the new developments and incorporated them in the designs of the Navy types "A" (60-600 kc.), "B" (30-300 kc.), and "C" (1,200-3,000 kc.) receivers. These were completed in early 1915 and placed in production at the Washington Navy Yard in the same year.14
The Cohen method was used. This consisted of coupling and a modified type of feedback circuit, with a coil in the plate circuit for the purpose of making the vacuum tube oscillate. To avoid the use of the term "feed-back," Clark termed it "a 'tickler' because it tickles the audion and makes it quiver."15 The leads were of solid wire capable of withstanding shipboard vibration and the shock of gunfire. The induction coils were of low resistance as compared with those used in commercial receivers and their values in the two circuits could be varied to provide sharp tuning. Dials were fixed to the shafts of the tuning condensers making it possible to calibrate each receiver so that the operator could tell where to align it for specific frequencies. Arrangements were incorporated to permit the use of either crystal or vacuum tube detection.
These receivers were placed in service at the shore stations and on the more important combatant ships as fast as they could be manufactured. However, economy dictated the continued use of the crystal detector, and the heterodyne feature was used only for the reception of the continuous wave signals.16
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3. NAVY PLANS TO DESIGN AND MANUFACTURE RADIO EQUIPMENT FOR ITS OWN USE
Finally, it was decided early in 1913 that the Navy would proceed, design and manufacture radio equipment for its own use. From the patent standpoint the Navy was in no different position than any other contractor and the Marconi and other interests would have been quick to claim infringement of their basic patents. At this time Dr. Louis Cohen, famed for his work with Dr. Austin in developing the empirical formula for the determination of signal strength at specific distance from transmitting source, completed the development of a receiver utilizing a new method of coupling, using condensers instead of inductance coils. In February 1913 the Bureau of Steam Engineering obtained rights from Cohen and procured his services to assist in the designs of receivers.
Receiver designs were completed prior to February 1915 but, during the interim, many things occurred which improved radio reception, among them the development of the three-element tube as an oscillator and amplifier and the feedback circuit as a means of controlling oscillations. The heterodyne method of reception became more feasible because better regulation of this circuit could be obtained by use of the feedback circuit. The use of the three-element tube in stage amplifiers provided better means of bringing in weak signals. All of these developments were incorporated in the naval receiver designs and the utilization of some of these were definite infringements. The increased requirements for radio equipment, brought about by the preparedness program and our later entry into the war, were too large for naval manufacturing facilities, and necessitated continued contracting with commercial manufacturing concerns for equipments based on naval designs.
Additionally, the Navy was licensed under the Cohen coupling patent and the Hazeltine neutrodyne circuits.