Selector Module Assembly

TM 11-5895-1141-34

by the selector module assembly may be accessed by the radio channel equipment. J201 and J202 are identical

receptacles each having 32 contacts arranged in a 2 x 16 array. This array is divided along its length into four 2 x 4

contact groups which for purposes of identification shall be referred to as Group I, II, III and IV. Group I contains contacts

1 through 4 and 17 through 20. Group II contains contacts 5 through 8 and 21 through 24. Group III contains contacts 9

through 12 and 25 through 28. Group IV contains contacts 13 through 16 and 29 through 32. Seven conductors

extending from the module receptacles to each contact group carry the transmitter audio pair, the receiver audio pair, the

transmitter keying pair and the interlock bus conductor. Because of its small size and short cable runs therein, the audio

pair of the wiring within the selector unit assembly are twisted but not shielded. Therefore, there is no connection present

to the eighth contact of each group (2, 6, 10 and 14). These contacts are used, however, in the mating connectors of the

interposition cable assembly to carry through connections from the shields surrounding the audio pairs of the cables to

suitable terminators at the radio channel equipment.

e. Selector Module Assembly. Refer to figure FO-17. For brevity of discussion the basic component numbers

shown on the diagram will be used, although their actual designation numbers are the basic numbers added to 1000 so

that module plug shown as P1 is actually P1001. Power supply voltage from the audio unit assembly is delivered unfiltered

to pin P1-3 and via the audio unit's filter to pin P1-23, with returns for the unfiltered and filtered supply loops brought to pins

P1-20 and P1-19. This serves to isolate fluctuations of power supply current, caused by operation of lamps and relays

from the amplifier supply buses, minimizing noise in the audio circuits. On the module front panel are two switches and a

multisection indicator light. Switch S1 is a three position toggle switch which is off when in the center position. It can be

set to the upper or lower position to route received audio signals to the loudspeaker or headset amplifiers. Switch S2 is a

three-position toggle switch which is off when in the center position. It can be set in the upper LOCK position to enable

selection of the channel controlled by the module. It can be moved downward to NONLOCK to accomplish the same

function but it will not lock there, and returns to center as soon as the handle is released. The remaining circuits in this

module perform the following functions: lamp display, audio signal circuits, syllabic indicator lamp driver, and interlock

circuits.

(1) Lamp Display. Refer to figure 2-7. Three lamps are located in the indicator assembly. One illuminates the

green quarter-section, one illuminates the red-quarter-section and one illuminates the amber lower half-section. Transistor

Q7 is an emitter follower which supplies current to the lamps at a voltage which is established by the setting of the

brightness control of the microphone amplifier/lamp brightener module assembly in the audio unit assembly. The range of

the lamp voltage is

2-18