TUNING SYSTEM RADIO SET AN/ARC-131-continued

TM 11-5820-670-30

1-61. TUNING SYSTEM RADIO SET AN/ARC-131. (CONT)

These lines are grounded in various combinations at the control unit to provide required tuning for the

particular frequency.

When the manual frequency selector switches are positioned to 30.00 MHz, as shown in FO-19,

grounds are applied to tuning control lines MHz select A, MHz select E, 0.05 MHz select A, 0.05 MHz

select E, and band

lines for the receiver-transmitter and antenna coupler.

Tuning control line select B, MHz select C, select D, and band

selection lines are not grounded in

30.00 MHz position. Tuning control line MHz select A receives a ground through the front wafer of

S9102E and rear wafer of S9101A. The ground is applied through pin k of connector J9101, pin 26 of

P9601, and pin 6 of P9701 to pin 6 on the rear wafer of S9705 in the gearbox.

If the radio set were tuned to some frequency other than 30.00 MHz, pin 6 may be making contact with

the switch wiper. Pin 4 will always remain in contact with the wiper. The ground signal would then be

applied through pins 6 and 4 of S9705 (rear wafer) to the emitters of Q9703 and Q9704.

Tuning control line MHz select E also receives a ground through the front wafer of S9101A in the con-

trol unit. The ground is applied to pin 5 on the front wafer of S9705 in the gearbox through connectors

J9101 pin CC, P9601 pin 24, and P9701 pin 4. This ground signal is also received at pin 4 on the rear

wafer of S9705 since two rotors are electrically connected. The application of the ground signal to the

emitter of Q9704 causes the transistor to conduct; both transistors are necessary to ensure that S9705

will be positioned correctly for the frequency selected.

When relay K9702 energizes, either a ground or + 27.5 vdc will be connected through contacts 1 and 6

to motor B9703. The signal applied through the contacts is determined by the condition of motor re-

versing relay K9703. Application of + 27.5 vdc causes motor B9703 to run and in turn rotate S9705 by

means of the gear train until its rotor is disconnected from pins 5 and 6 of S9705 as shown in FO-19.

With an ungrounded emitter, Q9704 stops conducting, K9702 deenergizes, and + 27.5 vdc is removed

from B9703.

Concurrent with grounding of the tuning control lines MHz select A and MHz select E, the tuning con-

trol lines 0.05 MHz select A and 0.05 MHz select E receive ground signals. Both control lines are

grounded through the front and rear wafers of S9103A and S9104A of the control unit. The ground for

0.05 MHz select A tuning control line is applied through connectors J9101 pin P, P9601 pin 28, and

P9701 pin 8 to contact 7 on switch S9703 in the gearbox. The ground received by 0.05 MHz select E

tuning control line is applied through connectors J9101 pin U, P9601 pin 27, and P9701 pin 7 to con-

tact 3 of switch S9703. Tuning control lines 0.05 MHz select B and 0.05 MHz select D are not

grounded at the control unit in the 30.00 MHz position.

Considering again that the radio is tuned to some frequency other than 30.00 MHz, either contact 3 or

7 of switch S9703 will make contact with the switch rotor. The ground signal is applied through contact

8 to the emitter of Q9702.

Motor B9702 and switches S9703 and S9704 comprise the Iedex assembly. Application of the ground

signal to the emitter of Q9702 causes Q9701 and Q9702 to conduct; both transistors are necessary to

ensure switch S9703 will be positioned correctly for the frequency selected.

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