Specifications

Figure 7. Schmitt trigger circuit, schematic diagram.
and rheostat R7816
a. Resistor R7817
form a voltage divider. Rheostat R7816 is
adjusted SO that the minimum source volt-
age will cause the line voltage sensing
circuit to function. Transistor Q7806 is a
unijunction transistor. When the power
source voltage is below minimum, the +16
volts dc applied at base B2 of Q7806 biases
it to cutoff. If the power source voltage
reaches or exceeds the minimum, the
voltage applied at the emitter of Q7806
overcomes the +16-volt bias and there will
be conduction through base B2 and load
resistor R7818 to ground.
b. At the instant Q7806 conducts, a sharp
positive-going pulse is generated at B1.
The pulse is coupled through capacitor
C7802 to the gate of dc switch CR7803. D
C
switch CR7803 is cut off until a positive
pulse is applied to its gate. Since CR7803
is in series with the +16-volt dc supply
line, operation of the TS-1777/VRM-l is
not possible until Q7806 generates a pulse
large enough to operate the gate of CR7803.
Resistor R7819 is the dc return resistor
for the gate circuit.
12. Power Distribution
(fig. 38)
Test Set, Radio AN/VRNI-l is supplied
26.0 volts dc from a power source such as
a vehicular electrical system. The CX-
7899/VRM-1 connects the power from an
MT-1029/VRC or MT-1898/VRC to the
TS-1777/VRM-l and to the R-442/VRC,
RT-246/VRC, or RT-524/VRC under test.
Figure 38 is a simplified power distribu-
tion diagram of a typical test setup for an
RT-246/VRC or RT-524/VRC. The setup
for testing an R-442/VRC is similar ex-
cept that an MT-1898/VRC is used instead
of an MT-1029/VRC .
a. The negative terminal of the vehicular
electrical system is connected to ground in
the MT-1029/VRC through terminal A of
J21. The positive terminal is connected
to terminal B of connector J21 on the MT-
1029/VRC; through fuse Fll to terminal
B of connector J24. The positive voltage
is connected by the CX-7899/VRM-l to
terminals B, C, and J of connector P401
on the RT-246/VRC or RT-524/VRC to
provide power and control voltage for the
equipment under test. The positive voltage
is also connected by the CX-7899/VRM-l
to terminal B of POWER connector J7902
on the TS-1777/VRM-l.
b. When switch S7901 is ON, positive
voltage is applied through fuse F7901 and
diode CR7901. Fuse F7901 protects the
TS-1777/VRM-l and associated equip-
ment. Diode CR7901 prevents possible
damage to the TS-1777/VRM-l if power of
improper polarity is accidentally applied
to connector J7902. The positive voltage
appearing at diode CR7901 is applied to
voltage dropping resistor R7901 and
breakdown diode CR7902, which form a
+16-volt dc regulator. The regulated +16
volts dc is applied to terminal C of con-
nectors J7907 and P7801. The voltage at
10