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TM 11-5820-695-35
(+5v). The output signal from A6 is coupled to the base
negative pulse output signal. Capacitor Cl is a supply
of Q1 through bias resistor R8. When the output from
voltage filter. The functions of capacitors C12 and C13
A6 is +5v, Q1 is turned on and output signal 1CRLFAIL
and resistors R18 and R19 at 48-channel baud
is logic zero (normal). Lamp DS1 is lighted because it
generator  Al  are  similar  to  the  functions  of
has a ground connection through Q1. When the pcm
corresponding parts at A5.
signal fails, A6 times out and the output signal at pin 8
returns to Ov.  Q1 is turned off and output signal
g.
Lamp Driver.  The -6 volt supply voltage
1CRLFAIL is logic one (alarm condition). Lamp DS1 is
through resistor R28 speeds up transitions from high
turned off but it has a quiescent current through resistor
(logic one) to low (logic zero) at the input of A10C.
R5 which keeps the filament warm. This reduces the
Resistor R29 provides a current to keep lamp DS1 warm
current surge through Q1, when Q1 and DS1 turn on.
when the output of A4A is high. When the output of
A4A returns to low, the current surge through A4A is not
c.
Voltage Filtering Components.
Voltage
as great due to the lamp warming current.
filtering components L1 and C1, C2 and C3 limit the
coupling of switching transients and other stray signals
h.
Voltage Filtering Components.
In the
to the power supply circuits.
synchronous
mode
(1A12A3)
voltage
filtering
components (L1 through L4 and C17 through C24) limit
2-44.  Alarm Monitor 1A12A5 and 1A12A15 Circuit
the coupling of switching transients and other stray
signals to the power supply circuits. The +6 volt supply
Theory (fig. 533 and 5-33.1)
for A8 is derived internally by dividing the +12 volt
supply voltage. This is accomplished by resistor R20
The integrated circuits used in alarm monitor 1A12A5
and zener diode CR13.  This voltage is filtered by
and 1A12A15 are shown functionally in figure 5-33 for
capacitor C14. In the asynchronous mode (1A12A14),
the synchronous mode and in figure 533.1 for the
the +5vdc supply voltage is filtered by L1 and C3, C4
asynchronous mode.  Figures 533 and 533.1 also
and C5.
specify each integrated circuit type.
Figure 6-24
provides a circuit diagram for each type of integrated
2-43.
Cable Digital Processor 1A12A4 Circuit
circuit used in Radio Set AN/GRC-144. The complete
functional description of the alarm monitor is provided in
Functioning (fig. 5-32)
paragraphs 2-5f and g and 2-6h and i.  Electrical
operation of discrete parts not discussed in paragraphs
Cable digital processor 1A12A4 contains integrated
2-5f and g and 2-6h and i is provided in a, b, and c
circuits designated Al through A6. Figure 5-24 provides
below which apply specifically to the synchronous mode
a diagram for each type of integrated circuit used. The
(1A12A5); however, they apply also to the asynchronous
complete  functional  description  of  cable  digital
mode (lA12A15) since the only change is that the
processor 1A12A4 is provided in paragraph 2-5c.
reference designators of the logic circuits are different.
Electrical operation of discrete piece parts is provided in
The cable traffic detector is discussed in d (1A12A5)
subparagraphs below.
and d.1 (1A] 2A15) below. The circuit description for
voltage filtering components in the asynchronous mode
a.
Level Converters.  Resistors R1, R2, and
(lA12A15) is similar to that provided in e below for the
R3 of level converter 1 are voltage dividing resistors
synchronous mode (1A12A5).
that also provide impedance matching for the 1TRPCM
output signal. The logic zero output is 0 volts to 0.5 volt
a.
Lamp Drivers.  The lamp driver circuits
at 15.5 ohms impedance. The logic one output is 1.5
conduct 40 ma.  to operate the 28 vdc lamps with
volts at 22 ohms impedance.  In level converter 2,
standard logic inputs.  Each circuit is a simple npn
resistors R9, R10 and All perform a similar function for
transistor inverter with a series 150 ohms collector
signal 1RRPCM.
current limiting resistor (required to limit the current
surge because of a cold filament when turning on the
b.
Alarm Circuits. In alarm circuit 1, resistor
lamp).  When the input is a standard logic one, the
R7 connects the +5v supply to A6 and capacitor C5 is a
transistor is saturated and the lamp driver provides
supply voltage filter.  Resistor R4 and capacitor C4
maximum current (40 ma.). When the input is a logic
determine  the  time  constant  for  monostable
zero, the transistor is cut off and the output is open
multivibrator A6 and thus determine the duration of the
(equal to lamp supply voltage).
logic one output (pin 8) when the input (pin 1) goes
negative.  If the pcm signal is active, this occurs
constantly and the output of A6 remains at logic one
2-82
Change 1


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