Image from page 458 of "The Bell System technical journal" (1922)
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Fig. 9—New York technical control positions. The Ship Station The Leinathans radio transmitter was designed to supply about500 watts, 80 per cent modulated radio frequency power to an antennaat frequencies from 3 to 17 megacycles. To insure satisfactory operat- RADIO TELEPHONE SERVICE TO SHIPS AT SEA 419 ing conditions, the carrier frequency stability was made as good as thatrequired for point-to-point service and the transmitter has been de-signed with the object of holding the frequency within 0.01 per cent.This facilitates the establishment of contact between the ship and shoreand obviates the necessity for frequent retuning of the shore receiver.The background noise on the unmodulater carrier, due to commutatorripple, etc., is inappreciable and the audio-frequency characteristicsfrom 200 to 2750 cycles is flat to within ± 2 db. In addition to these electrical requirements, the mechanical designmust be such as to withstand ships vibration, permit easy access to the
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Fig. 10—New York traffic positions. interior so as to facilitate wave change, and at the same time protectthe operators from electrical shock. The transmitter consists of a crystal oscillator and associated am-plifiers. The crystal provides the necessary carrier frequency accuracyand stability and the amplifiers step up the power of the carrier to thedesired level. Audio-frequency filters are placed in all voltage supplycircuits to eliminate background noise. The modulation system withits associated transformers is designed to produce the requisite audio-frequency quality. A diagram of the circuit is shown in Fig. 11. Very thorough electrical shielding is necessary between amplifierstages to prevent singing. This shielding makes the changing of coils, 420 BELL SYSTEM TECHNICAL JOURNAL which is necessary for the changing of wavelengths, very unhandy, andhence the crystal control and amplifier system, except the last stageis provided in duplicate, one side being used for the longer an
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