Telephone Interface

TM 11-5895-1141-34

control R1150, which is also located on the module's front panel. The signal is then delivered to the audio unit's built-in

speaker via the speaker amplifier assembly. This is a separate plug-in assembly located inside the audio unit and consists

of a five-transistor power amplifier Q1401 through Q1405. Note that the busy tone oscillator is located in the volume

control module and when enabled, injects the busy tone into both U1102 and U1105 insuring the operator receives the

tone either in the headset or loudspeaker.

e. Telephone Interface. Connections from the headset amplifier output are brought out to terminal pair E, F of

connector J103 for connection to a telephone circuit (if used) carrying this function. Two additional terminal pairs A, B and

C, D on J103 are provided for connection of incoming auxiliary signals to the input of the amplifier U1301 in the recorder-

monitor module.

f. Recorder-Mixer and Monitor Functions. Refer to figure 2-5. Amplifier U1301 is an operational amplifier connected

in a summing (mixing) mode to enable it to receive, in this application, signals from three separate sources and still keep

these sources isolated one from the other. These sources are the headset and loudspeaker amplifiers, the microphone

amplifier, and two auxiliary inputs (if used). The output of U1301 is delivered via transformer T1803 and pin pair 5, 6 to

pins H and J of J104 to which the recorder input terminals are connected. The monitor output terminals of the recorder

(not furnished) deliver a replica of the mixer amplifier U1301 output signal being recorded to the input of the monitor lamp

driver circuit, Q1301 and Q1303, via J104-B, C and transformer T1303. This signal causes the indicator lamp on the front

panel of the recorder-monitor module assembly to flash at a syllabic rate with an intensity corresponding to the input signal

level. If not required, the recorder-monitor module assembly may be left out with no effect on system operation.

g. Indicator Lamps. There are three miniature incandescent lamps mounted on the front panel of the selector unit in

a multi-section indicator lamp display. These lamps are DS1001 (green), DS1002 (amber) DS1004 (red). At the top left of

the display, DS1001 turns on whenever the enabling switch S1002 is positioned either in the LOCK or NONLOCK position.

Lamp DS1004 is located in the upper right part of the display. When the interlock bus drops low during channel

transmitter keying, DS1004 is turned on. DS1002 occupies the lower left part of the display. This lamp is referred to as

the syllabic indicator lamp because the lamp flashes at a slow rate to indicate the presence of incoming audio from the

receiver. The lamp intensities are adjustable using the LAMP BRIGHTNESS control mounted on the front panel of the

audio unit.

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