system. A central amplifier system is used to broadcastorders or information simultaneously to a number ofstations. An intercom system is used for two-waytransmission of orders or information.GENERAL ANNOUNCING SYSTEMThe basic MC circuit is the 1MC shown in figure4-12. This is the general announcing system, over whichword can be passed to every space in the ship. The ship’salarm system is tied into it as well. Transmitters arel o c a t e d o n t h e b r i d g e , q u a r t e r d e c k , a n d D Ccentral/central control station; additional transmittersmay be located at other points.The OOD is in charge of the 1MC. No call may bepassed over it unless it is authorized by the OOD, theexecutive officer, or the captain, except for a possibleemergency call by the damage control officer.Normally, the 1MC is equipped with switches thatmake it possible for certain spaces to be cut off fromannouncements of no concern to them. The captain’scabin, for instance, should not be blasted with calls forindividuals to lay down to the spud locker. The BMOWis responsible for passing the word over the 1MC. If theBMOW is absent and you are required to pass the wordyourself, be sure you know which circuits should be leftopen. Some parts of the ship have independent MCcircuits of their own, such as the engineers’ announcingsystem (2MC) and the hangar deck announcing system(3MC).The bullhorn (6MC) is the announcing system fromone point to another. It can be used to communicatebetween two ships. It is a convenient means for passingorders to boats and tugs alongside or to line-handlingparties beyond the range of the speaking trumpet. If thetransmitter switch is located on the 1MC control panel,you must be careful to avoid accidentally cutting in thebullhorn when you are passing a routine word.The 1MC, 2MC, 3MC, and 6MC are all one-waysystems. A partial list of loudspeaker systems is shownin table 4-2.INTERCOMSMC circuits, such as the 21MC (commonly knownas “squawk boxes”), differ from the preceding systemsin that they provide two-way communications. Eachunit has a number of selector switches. To talk to one ormore stations, you only need to position the properswitches and operate the PRESS-TO-TALK switch. Ared signal light mounted above each selector switchshows whether the station is busy. If it is busy, the lightflashes; if it burns with a steady light, you know that thestation is ready to receive. Typical IC circuits are asfollows:4-14Student Notes:Figure 4-9.—Dial terminal.4MC DC19MC Aviation ready room20MC CIC21MC Captain’s command22MC Radio central24MC Flag officer26AMC Machinery control
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