TM 11-5805-356-34-1
and the high and low voltage sections is identical
voltage across the primary of transformer T1.
with that described for an ac power source.
From this point on, operation of the transformer
Section II. SCHEMATIC DIAGRAM, TH-22/TG
operated in mode two, providing a shorter time-
2-5. Send Circuit
delay for the faster telegraph signal speed.
(2) At the beginning of a mark signal,
a. Delay Amplifier A1Q1.
transistor A1Q2 is turned off, and its collector
(1) Telegraph signals are applied through
voltage rises to +18 volts. Capacitors A1C3 and
current-limiting resistor A1R2 to the base of
A1C4 charge through collector load resistor A1-
transistor A1Q1. When a space signal (open, no
R7 of transistor A1Q2. The voltage rise across
voltage) is applied to the SEND jack (J1 or J2),
capacitors A1C3 and A1C4 delays the leading
0 volt on the base of transistor A1Q1 cuts A1Q1
edge of the mark pulse applied to the base of
off; the +1.8 volts on its collector is applied to
transistor A1Q3. When a mark-to-space transition
the input of the following stage (A1Q2). When
occurs, transistor A1Q2 is turned on and the col-
a mark (closed circuit) is applied to the SEND
lector voltage drops; capacitors A1C3 and A1C4
jack, transistor A1Q1 is turned on. This places
discharge rapidly through conducting transistor
the base of transistor A1Q2 at a very low volt-
A1Q2.
age. Resistors A1R1 and A1R3 provide base and
(3) Resistor A1R6 couples the control sig-
emitter bias, respectively. Resistor A1R4 is the
nal generated by break-in circuit multivibrator
collector load resistor. Capacitors A1C1 and A1-
A2Q8-A2Q9 from the output of buffer amplifier
C2 provide a time-delay (fig. 2-3) for the in-
A2Q7. When the multivibrator is set, indicating
coming signals. When the TH-22/TG is oper-
that a break-in signal haa been detected, a posi-
ated in MODE TWO, capacitor A2C2 is removed
tive voltage is applied to the base of delay am-
from the circuit, reducing the time-delay for the
plifier A1Q2 through resistor A1R6. This voltage
faster transmitting speed.
takes control over the transistor operation, caus-
ing the transistor to conduct continuously and
(2) At the beginning of a space signal,
forcing the transistor to remain in a state corre-
transistor A1Q1 is turned off, and the collector
sponding to a space input regardless of the input
voltage rises to +18 volts. Capacitors A1C1 and
applied at the SEND jacks.
A1C2 charge through collector load resistor A1-
c. Emitter Follower A1Q3. Emitter follower
R4 of transistor A1Q1. The slow voltage rise
A1Q3 isolates the modulator from the input cir-
across capacitors A1C1 and A1C2 delays the lead-
cuits. The input signal, developed across capaci-
ing edge of the space pulse applied to the base
tor A1C3 is fed through current-limiting resistor
of transistor A1Q2. When space-to-mark transi-
A1R11 to the base of transistor A1Q3. When
tion occurs, transistor A1Q1 is turned on, the
transistor A1Q3 conducts (mark signal at the in-
collector voltage drops and capacitor A1C1 rapid-
put), the emitter becomes more positive. When
ly discharges through conducting transistor A1-
the incoming signal at the input is a space,
Q1.
transistor A1Q3 is cut off, making the emitter
b. Delay Amplifier A1Q2.
less positive.
d. Modulator A1CR1-A1CR2.
(1) Input to amplifier A1Q2 is developed
(1) The modulator circuit changes the oper-
across capacitors A1C1 and A1C2. The positive
ating frequency of, the oscillator in response to
voltage at the base required to turn transistor
the incoming mark-space signals by connecting
A1Q2 on is applied through base bias resistor
and disconnecting capacitors A105-A1C7 across
A1R5. The pulses that appear at the base of
the tank circuit of the oscillator. With a space
transistor A1Q2 are amplified and developed
input, the capacitors are connected and the op-
across load resistor A1R7 and capacitor A1C8.
crating frequency of the oscillator is 1282.5 Hz.
Voltage divider A1R8, A1R9, and A1R10 sup-
With a mark input, the capacitors are discon-
plies emitter bias for transistor A1Q2; variable
nected and the operating frequency of the oscil-
resistor A1R9 allows this bias voltage to be ad-
lator is 1817.5 Hz.
justed to the proper operating level. Capaci-
(2) The connection and disconnection of the
tors A1C8 and A1C4 help provide the time-delay
capacitors is controlled by diodes A1CR1 and A1-
for the input telegraph signal. Capacitor A1C4 is
CR2. When the diodes conduct, the capacitiors are
removed from the circuit when the TH-22/TG is
connected to the circuit. When the diodes are
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