orders 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 infigure 4-12. This is the general announcing system, overwhich word can be passed to every space in the ship. Theship’s alarm system is tied into it as well. Transmittersare located on the bridge, quarterdeck, and DCcentral/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 known as“squawk boxes”), differ from the preceding systems inthat they provide two-way communications. Each unithas a number of selector switches. To talk to one or morestations, you only need to position the proper switchesand operate the PRESS-TO-TALK switch. A red signallight mounted above each selector switch shows whetherthe station is busy. If it is busy, the light flashes; if it burnswith a steady light, you know that the station is ready toreceive. Typical IC circuits are as follows:4-14Student Notes:Figure 4-12.—Loudspeaker transmitter4MCDC19MCAviation ready room20MCCIC21MCCaptain’s command22MCRadio central24MCFlag officer26AMCMachinery control
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