MARINE RADIO TELEPHONE SERVICE 705 



output to the receiving line. This device makes it possible to deliver 

 higher speech volumes to the telephones on shore since it prevents the 

 operation of the receiving vodas relays on radio noise during the idle 

 intervals. It also prevents the high radio noise which would other- 

 wise result due to the increase in gain inserted by the automatic volume 

 control whenever the carrier is interrupted. 



It can be seen from this discussion that the use of the codan pre- 

 supposes suppression of the carrier of the distant transmitter except 

 when the user wishes to talk. This method of operation has been 

 adopted for this type of marine radio telephone service. 



A 10-kw. 220-volt three-phase 60-cycle alternator driven by a 

 Buffalo gasoline engine has been provided to furnish the necessary 

 emergency power supply in case the normal commercial supply fails. 



The frequency designated by the Federal Communications Com- 

 mission for use by ships communicating with the shore through the 

 Green Harbor radio telephone station is 2110 kilocycles. This carrier 

 frequency is maintained within limits of 0.025 per cent. 



Two crystals are provided and the circuit arranged so that the 

 receiver may be quickly adjusted to operate on either of two frequencies 

 by means of a local mechanical or an electrically operated remote 

 control. The receiver is so designed as to make possible boat-to-boat 

 conversations on a separate frequency. 



The signaling unit which is normally connected to the output of the 

 radio receiver consists of a selector operated under the control of an 

 arrangement of relays which in turn are controlled by incoming signal 

 pulses of 600 and 1500-cycle tones. The bell on each vessel is oper- 

 ated only in response to the particular code of pulses to which the 

 selector is adjusted. Arrangements are also included so that the 

 vessels of any one fleet may be called simultaneously. 



A motor generator set operates continuously while the vessel is 

 standing by for the reception of signals and furnishes 12- and 200-volt 

 power for the operation of the radio receiver and signaling unit. A 

 second motor generator set is automatically started when the handset 

 is lifted from the switch hook to place a call or in response to an in- 

 coming signal, and furnishes power to operate the transmitter. On 

 several of the smaller boats having 32-volt power supply with wide 

 voltage fluctuations, power supply equipment consisting of two 

 dynamotors operated from a 12-volt battery charged from the vessel's 

 storage battery has been employed successfully. 



The control unit for the radio telephone consists of a small panel on 

 which are mounted a switch for turning the set on and off^, a meter for 

 indicating antenna current, a manual volume control, pilot lamp 



