GEARBOX MECHANICAL TUNING ASSEMBLY

TM 11-5820-670-30

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

Conduction of Q9702 simultaneously applies a ground signal to the control coil of K9701 and through

diode CR9711. Contacts 4 and 6 of relay K9701 connects + 27.5 vdc to motor 69702 when K9701 ener-

gizes. Motor 69702 momentarily operates switch S9704 causing relay K9701 to momentarily energize

and reenergize. This action causes +27.5 vdc to be applied and removed from motor 69702 in

synchronism with switch S9704. Switch S9703 will step one position at a time and select the proper

crystals in the rf oscillator as motor 69702 stops and starts. The ground signal applied through

CR9711 energizes relay K9605.

Tuning control signals are also applied to the antenna coupler simultaneously with those to the gear-

box. The antenna coupler tuning control line MHz select A receives a ground signal through the front

wafer of switch S9102A and the rear wafer of switch S9101C. This signal is applied through connectors

J101 pin M and J101 pin E to the antenna coupler. Tuning control line MHz select E of the antenna

coupler receives a ground through the front wafer of switch S9102B and rear wafer of switch S9101 D.

The ground is applied to the antenna coupler through connectors J9101 pin AA and J101 pin A.

Proper band selection is accomplished by applying a ground signal to the appropriate band control

tuning line. In the case of 30.00 MHz, grounds are applied to band

tuning control lines for the

receiver-transmitter and antenna coupler. The receiver-transmitter band

tuning control line

receives a ground signal through the front wafer of switch S9101B. The signal is applied to one side of

motor 69701 through connectors J9101 pin G, P9601 pin 23, P9701 pin 3, and switch S9701.

The application of the ground causes motor 69701 to run until the mechanical linkage that operates

switches S9701 and S9702 reaches the proper position for band

selection. At this time, switch

S9701 will open and the motor will stop. The ground signal is also applied through diode CR9701 to

operate relay K9605. The antenna coupler band

tuning control line receives a ground through the

front wafer of switch S9101D. The signal is applied through connectors J9101 pin H and J101 pin F to

the antenna coupler.

GEARBOX MECHANICAL TUNING ASSEMBLY

See FO-20 while reading this section.

The gearbox train rotates four mechanical output tuning shafts to specific angular positions for each

frequency selected at the control unit. Motors 69702 and 69703 drive the tuning shafts and also rotate

open-seeking switches S9705 and S9703 which control 1 MHz and 0.05 MHz tuning circuits. In turn,

the open-seeking switches control the operation of the dc motors.

1 MHz TUNING

Motor 69703 drives tuning shafts on vhf tuner A1000, oscillator buffer A6000, and rf amplifier A6500

circuits and positions switch S9705. Input from motor 69703 drives a geneva gear assembly through a

speed-reduction gear train and slip clutch. The slip clutch acts as a safety device if the gear trains

bind. The geneva gear assembly consists of a drive shaft and spur gear and a slotted drive wheel. The

drive shaft spur gear is driven by a slip clutch through a speed-reduction ratio of approximately 4 to 1.

The drive shaft of the geneva assembly drives the slotted wheel. Each time the drive shaft rotates 360

degrees, the slotted wheel rotates 90 degrees. The geneva assembly output is used as one input to the

differential.

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