Daughter Board No. 3 Assembly 1A13A3 Circuit Functioning

TM 11-820-695-35

the recovered orderwire signal is coupled to the

alarm signal (1.1/1.6 kHz). The oscillator circuit is

orderwire circuits by transformer T2, resistors R10 and

comprised of transistor circuit Q7, 1.1 kHz tuned circuit

R9, and contacts 4 and 6 of relay K1. When a pan

Z1, and amplifier A1. Transistor circuit Q7 and 1.1 kHz

alarm condition occurs, the ground return is removed

tuned circuit Z1 form a modified Colpitts oscillator.

from pin H and relay K1 becomes deenergized. R11 is

Resistors R22 and R33 are a voltage divider and

a dropping resistor in the relay coil circuit. With K1

develop the bias on the base of Q7. R24, R25, and R26

deenergized, the ow-pcm bypass signal (pin D) is

are the Q7 emitter resistors and provide dc bias and ac

applied to the orderwire circuits by contacts 8 and 6 of

impedance. Potentiometer R25 controls the ac input

relay K1. Since the orderwire signal is part of the

level to amplifier A1. The oscillating frequency is

receiver traffic signal, orderwire communication is

determined by the 1.1 kHz tuned circuit. The oscillator

maintained when a pcm failure occurs.

turn-on signal is coupled through diode CR10 from the

multivibrator circuit Q1 and Q2, the MODULE TEST

switch on 1A13A1, or the TEST TONE switch on

b. Amplifier A1. Amplifier A1 (o.w. ampl 3)

1A13A1. When the oscillator is turned on, the 1.1 kHz

amplifies orderwire signals for application to the through

output of Z1 is fed back to the emitter circuit of Q7. The

orderwire transmit terminals (pins 11 and 12). The

amplified signal developed at the collector of Q7

recovered order wire 4 kHz input (orderwire test signal),

sustains oscillation. Capacitors C9 and C10 and R27

or the ow-pcm bypass signals are applied to the

and R24 couple the 1.1 kHz output to operational

noninverting input (pin 2) of amplifier A1 through

amplifier A1. R28 and R31 provide input loading for

capacitor C2. Resistor R2 provides symmetrical loading

amplifier A1. In addition, R31 and R128 form the

to the noninverting input of A1. The ow ampl 3 input

feedback path which determines the amplifier gain. R32

signals are applied to the inverting input (pin 1) of

is a bias load resistor. The A1 output is coupled through

amplifier A1 through capacitor C1. Amplifier A1 has an

resistor R35. C13 and C14 are stabilizing capacitors

input impedance of approximately 1 negohm and an

preventing high frequency oscillations. Amplifier A1 is a

output impedance of approximately 100 ohms. The

general purpose operational amplifier which provides

amplifier gain is approximately 100 which is determined

minimum distortion and isolates the oscillator from the

by resistor R1 and resistor R3. Capacitors C3, C4, and

output circuits. A circuit diagram of amplifier A1

C5, and resistor R6 provide stabilization. The output

(integrated circuit U5B770231X) is provided in figure 5-

(pin 5) is coupled to the through orderwire transmit

24.

terminals by capacitor C6, resistor R5, 3 kHz low pass

filter FL1, and transformer T1. Filter FL1 sharply

c. Filtering Components. C11, C12, and C17 are

attenuates signals above 3kHz, consequently, the 4 kHz

filter capacitors for the power supply circuits. C3 and C4

test signal cannot appear at the through orderwire

are spike suppression capacitors for high frequency.

transmit terminals. The 4kHz is routed to orderwire

amplifier No.

3 monitor circuits through pin E.

Resistors R6, R7, and R8 provide an impedance match

2-53. Daughter Board No. 3 Assembly 1A13A3

between the filter and transformer T1.

Circuit Functioning (fig. 5-42)

Daughter board No. 3 assembly 1A13A3 contains the

pcm alarm circuit and amplifier circuits A1 and A2.

c. Amplifier AS. Amplifier A2 amplifies orderwire

Each circuit is described in the following paragraphs.

amplifier No. 2 input signals for application to the

orderwire hybrid terminal (pin 8). Orderwire signals

NOTE.

(through orderwire receive and recovered orderwire) are

Amplifiers A1 and A2 are integrated

applied to the inverting input (pin 1) of amplifier A2

circuits (type MC1533G). A circuit

through capacitor C7 and resistor R12.

The

diagram is provided for these circuits

noninverting input (pin 2) receives the orderwire

in figure 5-24.

amplifier No. 2 inputs (pin 9) through capacitor C8.

Resistors R14 and R12 determine the gain of A2 and

R13 provides a symmetrical input into the non-inverting

a. PCM Alarm Circuit. The pcm alarm circuit

input (pin 2).

Capacitors C12 and C13 provide

(relay K1) connects either the recovered orderwire

stabilization. The output of A2 is applied to filter FL2

signal (pins N and S) or the receiver traffic signal (OW-

through C14 and R16. R17, R18 and R19 provide an

PCM BYPASS, pin D) to the orderwire circuits. For

output T pad for filter FL2.

normal conditions, a ground return is present at pin H

causing relay K1 to be energized. With K,1 energized,

2--91