Abstract
WHEN the radio telephone was first applied to ships at sea about 1929, the ship receivers, connected either to a loud speaker or an operator's headset, were always con the air’ and thus heard all calls. Stations were called by name, and all other stations listening on the same frequency would hear the call. With the increasing use of ship to shore radio service, a method of signalling one ship only became highly desirable, as this would obviate the necessity of keeping the loud speakers or telephone receivers ‘on the air’ all the time. In the Bell Laboratories Record of April a method of doing this is described. With this system, each ship has a three digit number assigned to it. When the operator at the telephone switchboard wishes to place a call, he merely dials the number of the ship wanted. This sends out a series of tone pulses which are received by all the ships within range. The called ship is the only one that receives an audible signal. On this ship a telephone bell rings and the operator picks his handset off the hook and replies in the usual way. When a call is answered, the handset is removed from its switch-hook, thus operating the transfer relay. This removes the selector set from the radio receiver and connects the telephone receiver in its place. It also stops the bell ringing. When the telephone conversation is finished, the handset is returned to its hook and this releases the relay. The signal receiving set is automatically reconnected in preparation for receiving calls. This system is now being used by a number of coasting and harbour ships in America, but it promises to become applicable to a much wider field.
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Dialling Ships at Sea. Nature 137, 900 (1936). https://doi.org/10.1038/137900c0
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DOI: https://doi.org/10.1038/137900c0