TM 11-6625-847-45
connector J2 from the emitter of A1Q5 by capacitor
verses + 20 volts dc and ground on the two pins of
A1C6. The positive (85 usec) output pulse is coupled by
connector J1 when switched from either REC or XMIT.
capacitor A1C7 from the collector of A1Q5 to connector
J3.
1-9. Pulse Generator Subassembly A2A1A1
c. The square wave output of transistor A1Q2 is
further amplified and shaped by transistor A1Q6. The
Note. Where partial reference designators are
output of A1Q6 is differentiated into a positive and
used, prefix with test set and pulse generator reference
negative pulse by capacitor A1C9 and resistor A1R18.
designator A2A1A1, unless otherwise specified.
The negative pulse is shunted to ground by diode
A1CR4. The positive pulse, coupled by diode A1CR5, is
a. The function of pulse generator subassembly
the input to a Schmitt trigger multivibrator consisting of
A2A1A1 is to supply to separate connectors on the front
transistors A1Q7 and A1Q8. The Schmitt trigger circuit
panel of the test set with a 1-usec wide positive pulse
provides a standard pulse output for each positive input
and either a 150-usec negative pulse or an 85-usec
trigger pulse. Variable WIDTH control resistor R4
positive pulse. Front panel controls on the test set
controls the duration of the output pulse of the Schmitt
adjust the width and amplitude of the 1-usec pulse and
trigger to 1-usec. The amplitude of the 1-usec output
the width and amplitude of either the 85-usec wide pulse
pulse is controlled by coupling a portion of the pulse
or the 150-usec wide pulse. The pulse repetition rate of
developed across collector load AMPLITUDE resistor
R3 and coupled by capacitor A1C12 to connector J4.
external audio signal generator connected to INPUT
connector J1.
1-10.
Dc-to-Dc Converter and Regulator Module
b. The input audio signal at INPUT connector J1 is
A2A3
connected to the base of first pulse shaper transistor
A1Q1 by capacitor A1C1. Transistors A1Q1 and A1Q2
are utilized as a pulse shaping circuit to shape the input
Note. Where only partial reference designator are
sine wave into a square wave. The output of the pulse
used, prefix with test set and dc-to-dc converter and
shaping circuitry, at the collector of A1Q2, is the input
regulator module reference designator A2A3, unless
to the base of transistor A1Q6 and to capacitor A1C3.
otherwise specified.
Diode A1CR3 connected between capacitor A1C3 and
the collector of transistor A1Q3 couples the positive
a. The function of dc-to-dc converter and regulator
portion of the square wave as the trigger input to the
module A2A3 is to produce all operating voltages
monostable multivibrator consisting of transistors A1Q3
required by the SM-442A/ GRC with the exception of the
and A1Q4. The negative portion of the square wave
+ 27-volt dc primary power.
input at capacitor A1C3 is shunted to ground by diode
A1CR2. Each positive trigger input to the multivibrator
b. In the regulator section, the +27-volt dc is
generates an output pulse by switching the multivibrator
applied to the collector of transistor 1A1Q1 on the
from the normal stable state to the unstable state for a
chassis of the test set and to pin 13 of J2. The effective
length of time depending on the setting of WIDTH
collector-to-emitter resistance of test set transistor
control resistor R2. The WIDTH control is used to set
1A1Q1, in series with the +27-volt dc line, drops the
the output of the multivibrator for either an 85-usec or
voltage to a constant +20 volts dc for any given current
(150-usec) duration pulse. The negative output pulse of
required by the external circuits. The value of the series
the multivibrator, at the collector of transistor A1Q4, is
resistance is determined by the rate of conduction of
the input to the base of inverter amplifier transistor
test set transistor 1A1Q1, controlled by the regulator
A1Q5. The amplitude of the pulse output of A1Q5 is
circuit.
The differential amplifier, consisting of
controlled by basebiasing resistor AMPLITUDE control
transistors A1Q3 and A1Q4, compares the output from
R1. The negative (150-usec) output pulse is coupled to
test set transistor
1-9
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