TM 11-5805-356-34-1
jack J4, REC jack J3, and telegraph receiving
A3Q6 is developed across emitter load resistor
equipment to the collector of transistor A3Q11;
A3R23.
it then flows through the closed electronic switch
g. Emitter Follower A3Q6 and A3Q7. The
(conducting transistor A3Q11) for mark signals,
discriminator output is applied to emitter follow-
completing the circuit. There is no current flow
er A3Q6, and the output of A3Q6 is applied to
for space signals. The magnitude of the receive
emitter follower A3Q7. This circuit filters the
loop current is controlled by adjusting INT.
carrier from the demodulated discriminator out-
BAT LOOP CUR resistor R12.
put signal and applies the clean signal to dc am-
plifier A3Q8. Filtering is performed by resistors
A3R24 and A3R25, together with capacitors A3-
C10 and A8C11. The output voltage, developed
across emitter resistors A3R26 and A3R27, is
c. 1180-Hz Filter Z1 and Emitter Follower
direct-coupled from the emitter of transistor A3-
A3Q1. The break-in signal is applied to the input
Q7 to the input of differential amplifier A3Q8
of the 1180-Hz filter from the primary of output
and A3Q10.
transformer T3. All signals except the 1180-Hz
h. Differential Amplifier A3Q8-A3Q10.
break-in signal are rejected by the filter. The
(11) This circuit operates electronic switch
1180-Hz output signal is applied through cou-
A3Q11 from either of two signal inputs. The
pling capacitor A2C1 to the base of transistor
first input is the telegraph signal for operating
A2Q1, an emitter follower, the output of which
the loop equipment. The signal is developed at
is develped across resistor A2R4 and is coupled
the emitter of transistor A3Q7 and applied to the
through to the input of dc amplifier A2Q2. Re-
base of transistor A3Q8. The second signal, from
sistors A2R1, A2R2, and A2R3, together with
the threshold circuit, locks the electronic switch
capacitor A2C2, provide base biasing and decou-
in the mark condition when the threshold circuit
pling for transistor A2Q1. Resistors A2R5 and
is activated by loss of signal level; the signal
A2R7, with capacitor A2C3, provide base biasing
from the threshold circuit is applied. to the base
and decoupling for transistor A2Q2. The output
of transistor A8Q10 through transistor ASQ9
of transistor A2Q1 is coupled through capacitor
A2C4 to the base of transistor A2Q2.
threshold signal at the base of transistor A3Q10
b. Dc Amplifier A2Q2, A2Q3 and Emitter Fol-
has precedence, and the electronic switch is oper-
lower A2Q4.
ated to the mark condition whenever the input
(1) Transistors A2Q2 and A2Q3 form a dc
signal is below the threshold level.
feedback amplifier, with resistor A2R9 providing
(2) The input signal applied to the base of
local feedback and resistors A2R10 and A2C5
transistor A3Q8 biases the transistor to the con-
providing emitter bias. The signal developed
ducting (mark) or nonconducting (space) state.
across collector load resistor A2R8 is direct-cou-
The on-off states of transistor A3Q8 bias tran-
pled to the input of transistor A2Q3, where the
sistor A3Q10 to an opposite state through com-
break-in signal is further amplified. Emitter re-
mon emitter resistor A3R29. When transistor A3-
sistors A2R12 and A2R14 provide local feedback,
Q10 conducts, a portion of the positive voltage
and resistor A2R13 provides the emitter bias. The
developed across collector load resistors A3R33
feedback voltage developed across resistor A2R14
and A3R34 is direct-coupled to the electronic
is coupled through resistor A2R6 to the base of
switch. An input signal applied to the base of
transistor A2Q2 for stabilizing degeneration. Ca-
transistor A3Q10 biases it to the conducting
pacitor A2C6 provides a dropoff in the bandpass
state, overriding the biasing voltage developed at
characteristics of the amplifier at the high fre-
the emitter by common emitter resistor A3R29.
quency end to prevent the possibility of oscilla-
Resistor A3R28 is the collector load for tran-
tion, The output of the amplifier is developed
sistor A3Q8.
across collector load resistor A2R11 and is direct-
i. Electrontic Switch A3Q11. This circuit pro-
coupled to the base of transistor A2Q4. Capaci-
vides the open and closed circuit connections re-
tor A2C7 is a bypass for emitter bias resistor
quired to operate the teletypewriter equipment.
A2R13.
Controlling voltage for the switch is applied to
the base of transistor A3Q11. This control volt-
(2) The break-in signal is applied to the
age biases the transistor to conduct (mark) or
base of emitter follower A2Q4. The output of
not conduct (space). When conducting, the cur-
the emitter follower is developed across emitter
rent flows from the +108-volt line through
load resistor A2R15 and is coupled through ca-
INT. BAT LOOP CUR resistor R12, EXT. BAT
pacitor A2C8 to the dc rectifier.
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