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
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
