TM 11-5805-689-14
quiescent state and will not be subject to latch up.
input amplifier. Transistor Q1 is a grounded emitter
The output of the squaring amplifier is coupled from
voltage amplifier. The output from the collector of
the collector of transistor Q4 to the base of detector
transistor Q1 is connected to the base of an emitter
t r a n s i s t o r s Q7 and Q8. The detector utilizing
follower, transistor Q2. Transistor Q2 superimposes
transistor Q8 is tuned for a resonant frequency of
current gain on the voltage gain accomplished by
2250 Hz by capacitor C5. The clipped portion of the
transistor Q1. A portion of the output taken from the
detector tanks passes through either diode CR11 or
emitter of transistor Q2 is fed back through resistor
diode CR12, through Zener diode CR13 to enter the
R1 to the base of transistor Q1 to stabilize the AC
base of transistor Q10. As the voltage across resistor
voltage gain of this stage. Since the alternating
R27 reaches the forward voltage of the base-emitter
current through resistor R1 is 180 out of phase with
respect to the alternating current flowing through
junction of transistor Q10 about 40 microampere
will pass through resistor R27 and the remainder of
resistors R2 and R3, the AC voltage gain of this
the clipped current from the detector tank will pass
stage is described by the resistance ratio of resistors
R2, R3, and R1. Since resistors R2 and R3 equal 20K
through the base-emitter junction of transistor Q10.
The product of this base current (IB1 0) and the
resistance and resistor R1 equals 182K resistance,
the approximate voltage gain from the signal in-
current gain (HFE) of transistor Q10 will be con-
duced across resistor R3 to the signal appearing at
ducted by the collector of transistor Q10 to discharge
the emitter of transistor Q2 is equal to the resistance
capacitor C7 through resistor R30. The remainder of
the collector current ( IC10) passes through resistor
of resistor R1 over R2 and resistor R3, or 182K/20K,
o r 9.1, The loading effect of resistor R6 and
R28 to resistor R29 and the base of transistor Q12
capacitive reactance of capacitor C2 is considered as
a n d saturates its collector. The Vcc - Vsat. of
negligible across the dynamic resistance of the base-
transistor Q12 appears at test point 5 (TP5). A
emitter junction of transistor Q1. A second portion
p o r t i o n of the collector current (IC 1 2) p a s s e s
of the signal appearing at the emitter of transistor
through resistor R33 and the base of transistor Q13
Q2 is fed through resistor R8 to charge capacitor C2.
to saturate its collector. As the detector tank voltage
falls below the required value to cause diode CR13 to
Since the time constant formed by capacitor C2
looking into resistors R6 and R8 is long the voltage
conduct, the voltage across resistor R27 falls below
the required forward voltage to keep the base-
appearing across capacitor C2 will be essentially
emitter junction of transistor Q10 in conduction. The
constant. The purpose of the feedback network
collector current ( IC10), therefore, falls off and the
formed by capacitor C2, and resistors R6 and R8, is
current through R29 now serves to charge capacitor
t o lower the average voltage measured across
C7. The collector of transistor Q11 now draws
resistor R9. The design level for this voltage is 1.7
current through resistor R31. This current maintains
volts. If this value is too high or too low, premature
the voltage drop across resistor R28 to keep tran-
clipping of the waveform appearing across resistor
sistor Q12 turned on. The charging time constant of
R9 will occur and adversely affect the bandpass
capacitor C7 is sufficiently long that transistor Q11
characteristic of the 570 Hz, 2250 Hz, and 2600 Hz
and, therefore, transistor Q12 will remain in con-
detector tank circuits. The remainder of the AC
duction until the next positive going cycle of voltage
signal across resistor R9 is coupled by capacitor C3
across the detector tank reaches the voltage
to the base of transistor Q3. Transistor Q3 with no
necessary to cause diode CR13 to conduct and again
AC signal imposed on its base will be normally
inject current into the base of transistor Q10.
turned on. (The collector current of transistor Q3 will
Capacitor C7 will then again discharge through the
be equal to the current flowing through resistor R11
collector of transistor Q10 to repeat the cycle. The
l e s s the base current of transistor Q3 flowing
turn on delay circuit consists of transistors Q13,
through resistor R10 to resistor R20 to the positive
Q14, and Q15 along with capacitor C8, resistors
power termina1.) The bases of transistors Q3 and Q4
both refer to a nominal 1.2 volts held at the collector
R 3 7 , R33, R32, R36, and R39. The output of
of transistor Q5. This voltage represents the voltage
transistor Q12 is coupled through resistor R32 to the
drop across diode CR10 and the base-emitter forward
base of transistor Q14 and through resistor R33 to
voltage of transistor Q5, Q6 provides current from
the base of transistor Q13 and resistor R34. The
which this voltage is derived. Q6 also provides
action of this circuit is as follows. During the receipt
current for CR9. Resistors R16 and R17 make up a
of a seize, or acknowledge signal the collector of
voltage divider across CR9. The junction of this
transistor Q12 goes to a logic 1 condition. At this
voltage divider is tied to the base of Q4 whereas one
time, the current flow is through transistor Q12,
end of R16, the 1.2V, is tied to Q3 (through R10).
through diode CR18, resistor R33 and resistor R34 to
The arrangement assures that the squaring am-
ground. Base current is thus supplied to transistor
plifiers Q3 and Q4 will always be in the proper
Q13 causing it to conduct. Capacitor C8 immediately
3-4
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