Transmit Output and Carrier Alarm Circuits

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

board TB2. Diodes CR12 and CR13 permit output

and less current when the external temperature

transformer 1A1T1 to operate with a high-impedance

increases. Transistors Q1 and Q2 form a differential

output line.

OUTPUT switch 1A1S7 (in the

amplifier that provides a constant emitter voltage. The

600~position) connects resistor R38 across diodes

constant emitter voltage serves as the forward bias for

CR12 and CR13 to allow operation into a 600-ohm

transistor Q1, thereby allowing the maximum current

output line.

variations required by thermistor 1A1RT1. Resistor R1

is the collector resistor for transistor Q1.

When

b. Alarm, Circuit. The alarm circuit consists of the

transistor Q1 current increases, its collector voltage

level threshold circuit, the amplitude detector circuit, the

becomes more negative and increases the forward bias

2-second delay circuit, and amplifier IN-8.

on transistor A1Ql and therefore the current flow through

(1) Level threshold circuit. In this degenerative

the heater element. Diode CR1 functions as the emitter

amplifier (transistors Q4 and Q5), capacitor C2

resistance for transistor 1A1Q1. Resistors 1A1R3 and

and resistor R10 suppress any oscillations that

1A1R5 form a voltage divider to establish initial bias for

may occur. A positive-going signal applied to

transistor Q2.

the base of transistor Q4 increases Q4

b. If thermistor 1A1RT1 senses a rise in the

conduction, reducing its collector voltage. This

external temperature, its resistance decreases, so that

action reduces the forward bias on transistor

less current flows through transistor Q1. Consequently,

Q5; thereby decreasing Q5 conduction.

the potential at the collector of transistor Q1 becomes

Resistors R12 and R15 are emitter swamping

more positive, which increases the reverse bias on

resistors; resistors R9, R13, and R14 form the

transistor 1A1Q1and decreases the current flow through

collector load for transistor Q5. THRESHOLD

the heater element.

resistor 1A1R14 sets the minimum level

requirements of the circuit that will provide

5-13. Transmit Output and Carrier Alarm Circuits

sufficient output signal amplitude to operate the

(fig. 8-11)

amplitude detector circuit ((2) below).

(2) Amplitude detector circuit. This is basically a

a. Data Circuit. Input, fsk signals are applied

paraphrase amplifier (transistor Q6) and a

through OUTPUT LEVEL ADJ resistor 1A1R6 to the

bridge rectifier circuit, followed by a

output amplifier stage. Transistors Q1 and Q2 form a

regenerative amplifier (transistors Q7 and Q8).

differential amplifier. Base resistor R2 develops the

Resistors R16 and R17 provide initial bias and

input signal, emitter resistor R3 develops initial bias for

develop the input signal; capacitor C3 is the

the differential amplifier, and resistors R4 and R6 are

coupling capacitor. Transistor Q6 provides two

the collector load resistors for transistors Q1 and Q3.

outputs, 180° out of phase with one another,

Coupling transformer 1A1T2 is a 1-to-1 current ratio

that are coupled through capacitors C4 and C5

transformer, and capacitor C1 and resistor R5 form a

to the bridge rectifier (CR1 through CR4).

low-frequency alternating-current (ac) sensing network

Diodes CR5 and CR6, together with resistor

that provides degenerative feedback to transistor Q2.

R21, provide for a slight forward bias to diodes

The degenerative feedback on transistor Q2 forces

CR2 and CR3. Resistors R18 and R19 are the

transistor Q3 to assume the same high impedance for

load resistors for the paraphrase amplifier. As

both the mark and space frequencies, thus making the

long as an input signal of sufficient amplitude is

output at the secondary of transformer 1A1T2

applied to transistor Q6, a slight positive voltage

proportional to the input voltage (signal) to transistor Q1,

will be applied to the base of transistor Q7

regardless of the input signal frequency. Resistor R7 is

through either diode CR1 or CR4, depending on

the collector load for transistor Q3. The output signal

the polarity of the input signal. When the input

from transformer A1T2 is applied to BALANCED XMTR

signal is removed, transistor Q6 is cut off and

CARRIER OUTPUT terminals 12 and 13 of terminal

the bridge rectifier produces no output; the

Change 5

5-11