TM 11-6625-1633-45
network selected by INTERNAL MODULATION FRE-
2-3. Analysis of Modulation Amplifier Circuit
QUENCY selector switch S1. The input to the grid of
resistance-capacitance pentode oscillator V1 is deter-
mined by the negative (degenerative) feedback loop con-
a. The output signal from the internal modulator-
sisting of capacitor C25, resistor R27, and one of the
oscillator circuit (para 2-2) or from an external sine
bridge-tee networks. Since the selected bridge - network
wave or pulse source is applied through MODULATION
selector switch S2 and DEVIATION adjustment poten-
negative feedback to the grid of oscillator V1 is mini-
tiometer R35 to the grid of modulation amplifier A1V1.
mum at the tuned frequency.
DEVIATION adjustment potentiometer R35 controls the
input signal amplitude that is applied to amplifier AlV1.
b. Automatic amplitude control is maintained by
Trimming capacitor C29 controls the network (capacitor
positive (regenerative) feedback. This is developed
C29 and resistor R32) response to an external sine wave
through capacitor C23 and the amplitude control net-
modulating signal.
work consisting of resistors R14 and R15, capacitor
C22, and the voltage divider network comprised on lKC
b. The output of modulation amplifier AlV1 is ap-
potentiometer R16 resistor R17, and 1.6KC, 20KC,
plied through resistor AlR9 to the grid of cathode fol-
68KC, and 108KC potentiometers R18 through R21,
lower A1V2. Cathode follower A1V2 acts as an isola-
respectively. Potentiometers R16 and R18 through R21
tion stage between modulation amplifier AlV1, the re-
are used as adjustments to set the amplitude of the os-
flector of klystron oscillator A4V1, and the deviation
cillations at the selected frequency. Automatic voltage
metering circuit. A portion of the A1V2 output is fed
control for the cathode of oscillator V1 is obtained by
back to the grid of AlV1. Negative feedback is used to
constant temperature thermistor RT1, connected at the
stabilize the gain and reduce distortion introduced by
junction of 1 KC potentiometer R16 and resistor R17.
modulation amplifier AlV1.
Diodes CR28 and CR29, together with capacitor C51,
maintain a constant voltage through the filament (pins 3
2-4. Analysis of Deviation Metering Circuit
and 7) of temperature controlled thermistor RT1. When
a change occurs in the output signal amplitude, the re-
sulting current change varies the resistance of thermistor
a. When MODULATION selector switch S2 is in the
RT1. This, in turn, varies the cathode resistance of os-
INT SINE, EXT SINE, or EXT PULSE position, a por-
cillator V1 to maintain a constant output voltage.
tion of the modulated signal is applied to the deviation
metering circuit for measurement. The deviation me-
c. The output signal from oscillator V1 is connected
tering circuit consists of amplifier A1V3, two bridge
through resistor R23 to the grid of cathode follower V2,
circuits, and deviation meter M1.
which acts as an isolator between the oscillator and
modulation amplifier V3. Modulation amplifier V3 pro-
b. Operation of the deviation meter, for each perti-
vides a constant current source for the cathode follower.
nent position of MODULATION selector switch S2, is
The output of cathode follower V2 is fed back through
described below:
capacitor C23 and INTERNA I, MODULATION FRE-
(1) EXT PULSE position. The external pulse input
QUENCY selector switch S1C for automatic amplitude
is applied through switch S2C and METER PULSE
control. In addition, the output of cathode follower V2 is
SENS potentiometer A1R2 to the full-wave bridge recti-
applied through capacitor C28, resistor R28, and cou-
fier, consisting of diodes AlCR1 through A1CR4. The
pling capacitor C27 to MODULATION selector switch
rectified voltage is applied through out of three range
S2B.
resistors: AlR20, AlR21, or A1R22 (selected by the po-
sition of DEVIATION METER RANGE selector switch
S3) to deviation meter M1. Deviation meter M1, in se-
ries with the calibrating resistors and in parallel with the
NOTE
bridge, indicates a signal level proportional to the kilo-
hertz deviation produced by the modulating pulse.
Plate voltage is only supplied to the inter-
(2) INT or EXT SINE position. The internal or ex-
nal modulator-oscillator circuit when
ternal sine wave signal is applied through one of three
MODU-LATION selector switch S2 is in
frequency range resistors (A1R17, A1R18, or A1R19)
the INT SINE position.
2-2
