Alarm-Monitor 1A5 Circuit Functioning

TM 11-5820-695-35

circuit for the traffic signal consists of transistors Q5 and

follower Q3. Resistors R7 and R8 are in the emitter

Q6. When no signal is present, transistor Q6 conducts

circuit of Q2. C3 is an ac bypass capacitor.

and holds transistor Q5 off due to the voltage developed

across common emitter resistor R48. The incoming

Emitter Follower. Emitter follower Q3

peak-detected traffic signal will forward bias transistor

provides an impedance match between the second

Q5 when the magnitude of the peak-detected traffic

video amplifier and the output. Q3 also provides

signal exceeds the magnitude of the voltage developed

negative feedback to Q1. The amount of negative

across R48. When this occurs, the states will reverse

feedback determines the overall gain and band- width of

with transistor Q5 conducting and transistor Q6 off until

af-rf amplifier 1A4. The pcm signal is coupled by C4,

the peak-detected signal again drops below the voltage

R12 from the emitter of Q3 to the output jack (J2 OUT).

level of the common emitter resistor R48. The output of

The orderwire input signal from attenuator assembly

the Schmitt trigger is a series of positive square pulses

1A3 is also routed to the J2 OUT jack by P1-8. The

which are developed at the collector of transistor Q6.

combined pcm and orderwire signal is routed to the 4.5

These pulses are applied to the base of transistor Q7

MHz low pass filter (1A6) by the J2 OUT jack. The

and forward biases it into conduction. When transistor

alarm output (P1-9) is not used in af- rf amplifier 1A4.

Q7 is conducting, its collector is at a low level; this

provides a low impedance path to ground to light the

2-32.

Alarm-Monitor 1A5 Circuit Functioning (fig.

normal (green) traffic indicator lamp. The inverted

2-14)

output level at the collector of transistor Q6 is applied to

the alarm (red) traffic indication lamp. This transistor

The alarm monitor circuits are shown in

provides a low impedance path to ground for the alarm

figure 2-14. Low level alarm-monitor input signals are

lamp when no traffic signal is detected (quiescent state

amplified by operational amplifiers AR1, AR2 and AR4

of the Schmitt trigger circuit).

(fig. 2-14, part 3). Operational amplifiers AR1, AR2, and

AR3 are type U5B-770231X integrated circuits, see

The reflected rf power monitor signal is

figure 5-24. The amplifiers are connected in different

developed by a diode detector in directional coupler

configurations to accommodate each particular alarm

1,DC1 and coupled in pin 14 to the non-inverting input

monitor input signal.

The inverting input of the

pin 3 of operational amplifier AR2 (fig. 2-14(3)).

integrated circuit amplifier is pin 2, the non-inverting

Resistors R19, R20 and potentiometer R22 provide a

input is pin 3, and the output signal is taken from pin 7.

variable pad at the amplifier input. The incoming

The feedback resistance connected from the output pin

detected signal is also coupled through resistor RJ17

7 to inverting input pin 2 establishes gain of the

and out pin 15 to the meter selector switch on meter

amplifier.

panel assembly 1A15A8. Capacitor C10, at the non-

inverting input, integrates the input signal which is

NOTE

amplified and is coupled to the input of its associated

Schmitt trigger circuit by a jumper wire from pin P2-8 to

The alarm monitor is used in

pin P2-11 through series resistor R55 (fig. 2- 4(2)). The

position 2A12 of the R-1467/GRC-144

Schmitt trigger circuit consists of transistors Q8 and Q9

(refer to para 2-75).

which functions in an identical manner to Schmitt trigger

Q5 and Q6 previously described in b above with the

The traffic monitor signal from attenuator

exception that the normal indication is taken from the

assembly 1A3 is coupled in pin A3 to the inverting input

collector of Q9 and the alarm indication is taken -from

pin 2 of amplifier ARI1 (fig. 2-14(3)). Network C1 and

the collector of Q10. The presence of an input signal

R4, connected across the differential inputs pins 2 and

(high reflected power) will cause an alarm indication, the

3, provides lag compensation which increases the high

absence of an input signal (low reflected power) will

frequency response. The amplified traffic signal is

produce the normal indication.

applied to a diode peak detector circuit consisting of

capacitor C4, diodes CR11 and CR2, and capacitor C5.

The rf power monitor signal, representing

The positive peak-detected dc voltage forward biases

a sample of the forward power, is developed by a diode

transistor Q1 which couples the signal through

detector in directional coupler 1DC1 and

attenuator network R10, R11 and R12 to its associated

Schmitt trigger circuit on board A5 (fig. 2-14(2)). It is

also fed through R8 and pin 12 to the selector switch on

meter panel assembly 1A15A8. The Schmitt trigger

2-63