Initial Timer

TM 11-5805-424-15/NAVELEX 0967-220-9010/TO 31W2-2G-41

window timer, and a positive input to

approximately 0.75 second (adjustable by TALK

transistor Q5 in the window timer.

REQUEST WINDOW control resistor 1A1R10). If the

receive carrier alarm is actually a talk request, with a

(b) If the alarm condition does not remain for

duration of 1.5 second, both the initial timer and the

approximately 1 second, the circuits are

window timer are allowed to time out, lighting the front

reset to the original no-alarm condition

panel TALK REQUEST indicator lamp.

((1) above), and capacitor C1 discharges

b. Initial Timer.

through conducting transistor Q2.

c. Window T7imer.

(1) With a carrier signal being received by amplifier

IN-16, the negative input holds transistor Q1

(1) Initially, in the no-alarm condition, transistor Q5

conducting, thereby applying a ground to the

is conducting so that transistor Q6 conducts; this

input of transistor Q2. Transistor Q2 therefore

action prevents capacitor C2 from charging and

conducts and Prevents capacitor C1 from

transistor Q7 is held cut off. Circuit component

charging. Diode CR2 is reverse-biased and

functions for the window timer are essentially

holds transistor Q3 cut off, so that +15 volts is

the same as for the initial timer (b(2) above).

applied to the base of transistor Q4 keeping

(2) Approximately 1 second after an alarm

transistor Q4 cut off.

condition occurs, collector supply voltage is

(2) Resistors R2 and R3 provide initial bias for

applied to transistor Q7 from the initial timer

transistor Q1, and resistors R4 and R5 form the

(b(3) above). The positive voltage applied to

dc coupling circuit for transistor Q2. Diode CR1

transistor Q5 cuts off transistor Q5;

provides the emitter resistance, and resistor R6

consequently transistor Q6 is held cut off,

is a collector load resistor. Diode CR2 and

allowing capacitor C2 to charge toward +15

resistor R8 establish a positive feed through

volts through TALK REQUEST WINDOW

voltage level for transistor Q3, resistor R9 is the

control resistor 1A1R10. When capacitor C2

collector load resistor, and resistor R10 provides

charges sufficiently (in approximately 0.75

dc coupling between transistors Q3 and Q4.

second, as determined by TALK REQUEST

WINDOW resistor 1A1R10), transistor Q7

(3) When a talk-request (or carrier alarm) condition

conducts, placing a ground on the input of

occurs, a ground is applied, through pin H, to

amplifier IN-17, to cut off transistor Q8. If the

amplifier IN-16 and to diode CR6 of AND gate

alarm signal is actually a talk-request, the

GAD-3. The ground passed by diode CR6 cuts

positive input to diode CR6 of AND gate GAD-3

off amplifier IN-18, which does not affect

is removed after 1.5 second. With diode CR5

bistable FFB-1. However, the ground fed to

reverse biased by the -15 volts applied from

amplifier IN-16 cuts off transistor Q1;

amplifier IN-17, AND gate GAD-3 is inhibited,

consequently, transistor Q2 is cut off, allowing

allowing amplifier IN-18 to conduct (due to

capacitor C1 to charge toward +15 volts through

current flow through resistors R22, R23, and

DELAY control resistor 1A1R9.

R24). With transistor Q9 conducting, a positive

(a) If the alarm or talk-request signal persists

input transition (-15 volts to ground) is applied

for longer than 1 second (determined by

through coupling capacitor C4 and diode CR7 to

resistor 1A1R9), the charge built on

trigger bistable FFB-1; this action turns off

capacitor C1 is passed through diode

transistor Q11, which in turn causes transistor

CR2,

biasing

transistor

into

Q12 to conduct and apply a ground to light the

conduction. This action causes transistor

TALK REQUEST lamp.

Q4 to conduct and supply a positive

collector potential to transistor Q7 in the

Change 5

5-14