Figure 7-21.--Volume indicator meter.

and circuit 6MC are in use, (2) both circuit 1MC and

station. When an announcement is made from any

circuit 6MC are using the same amplifier channel, or

microphone control station, all loudspeakers selected at

(3) an alarm signal is being transmitted.

that station, except the loudspeaker in the immediate

area of the station, will receive the anouncement.

When both circuits are using the same

amplifier channel, circuit 1MC takes priority over

The loudspeakers associated with circuit 1MC

circuit 6MC. Therefore, if circuit 6MC is in use and a

are normally divided into four groups. These

circuit 1MC loudspeaker group is selected from

loudspeaker groups are designated (1) officers, (2)

another microphone control station and a

topside, (3) crew, and (4) engineering. There is only

transmission is initiated, circuit 6MC will be cut off.

one circuit 6MC loudspeaker group, with only one or

The announcement will then go out to the circuit

two loudspeakers installed.

1MC loudspeakers only.

After making an announcement over circuit

1MC, make sure you place the loudspeaker group

VOLUME INDICATOR METER.-- A

control switches selected in the OFF position. If any

volume indicator meter (fig. 7-21 ) is mounted on the

loudspeaker group control switch at any lMC

front of the microphone control station. This meter

microphone control station is left in the ON position,

indicates that the system is ready for use. his meter

announcements made from any other control station

also indicates the amount of output volume when a

will go out on those loudspeakers.

transmission is made. This meter is calibrated in

decibels from -10 dB through 0 dB to +6 dB. When

BUSY INDICATOR LIGHTS.-- Two busy

the press-to-talk switch on the microphone is

depressed, the meter needle should deflect. When an

indicator lights are mounted on the front of the

announcement is being transmitted, the meter needle

microphone control station, one for the 1MC (busy 1)

should deflect to 0 dB on peaks for normal volume.

and one for the 6MC (busy 2). These lights indicate if

the associated circuit is in use, thereby avoiding the

possiblity of initiating a call through that circuit.

Loudspeakers

Before making an announcement, make sure the

busy light for the desired circuit is not lighted.

Several different types of loudspeakers are

used with circuit 1 MC to suit different needs. In

Except in an emergency, do not attempt to

areas with comparatively low noise levels, such as

use circuit 1MC when the busy indicator light is

living spaces, low-power, radiator-type loudspeakers

lighted. If another microphone control station has

are used. On weather decks and in areas with high

already selected a circuit 1MC loudspeaker group(s)

noise levels, such as engineering spaces, high-power,

and is initiating an announcement, the transmission

folded-horn loudspeakers are used.

will go out to all loudspeakers selected at both

microphone control stations.

Circuit 6MC requires the use of a multiunit

straight-horn loudspeaker (fig. 7-22). This type of

When the circuit 6MC busy indicator light is

loudspeaker projects a narrow, powerful beam.

lighted, it will have no effect on circuit 1MC operation.

When both busy indicator lights are lighted,

three possible conditions exist: (1) both circuit 1MC

Figure 7-22.--Multiunit straight-horn

Figure 7-21.--Volume indicator meter.

loudspeaker.

7-18