is amplified by V10 and applied to modulator VII. The
The output signal of the second doubler is applied to
output signal of V11 is applied to saturable reactor L1.
third doubler V9 and to the FREQ. RANGEMC switch
The inductance of L1 is made to vary with the amplitude
which, when turned to the 100-200 mc position, makes
of the audio oscillations. Since L1 is connected across a
the output of the second doubler the signal generator
portion of the rf oscillator tank circuit, any change in the
output signal.
inductance of L1 produces a corresponding change in
e. Third Double. In a manner similar to that of the
r
the output frequency of the rf oscillator. The modulator
preceding doubler stages, third .doubler V9 amplifies
is capable of producing a maximum frequency deviation
and multiplies the frequency of the output signal of the
of 75 kc. After frequency multiplication by the first,
second doubler. The out put frequency of this stage is
second, and third doublers, the amount of deviation in
190 to 400 mc or eight times the fundamental oscillator
the rf oscillator output signal is a maximum1f50 kc
o
frequency. The output signal of this stage is available at
on the 50-100 mc range, 300 kc on the 100-200 mc
the RF OUTPUT jack when the FREQ. RANGE-MIC
range,600 kc on the 200-400 me range.
selector is set at the 200-400 mc position.
k. Surge Circui. The surge circuit, consisting of
t
f. Output Indicato.r A portion of the output signal
V16 and V17, applies a pulse of voltage to saturable
of the rf amplifier, the second doubler, or third doubler,
reactor L1 at the time the signal generator is turned on
depending on the setting of the FREQ. RANGE-MC
to reduce its indactance instantly to the p)roper
selector, is applied to the output indicator circuit. This
operating value.
circuit consists of a galvanometer connected in a bridge
circuit and is used as a visual calibrating device. A
center scale or SET TO LINE reading on the meter
rectifier circuit, furnishes a positive 400-volt de to the
indicates that the rf output is 100,000 microvolts.
voltage regulator circuit.
g. Audio Oscillato.r The audio signal which is used
m. Voltage Regulator The voltage regulator,
.
to frequency-modulate the rf oscillator is generated by
consisting of V12, V13, and V14, supplies regulated
audio oscillator V3 and V4. The frequency of oscillation
potentials of + 150 volts dc and + 200 volts dc for the
is controlled by the MODULATION switch. Oscillations
various circuits in the signal generator.
are produced at one of three fixed frequencies: 1,000
cps, 1,600 cps, or 20,000 cps. The output of the audio
42. Rf Oscillator V5
oscillator is applied to the deviation indicator and to the
deviation multiplier. The amplitude of the audio signal
rf pentode connected as a triode in a circuit equivalent
applied to these stages is varied by the DEVIATION
to a Colpitts oscillator. The oscillator has a frequency
control.
range of 23.75 to 50 mc. The frequency of oscillation is
h. Deviation Indicator The deviation indicator
.
determined by the tank circuit consisting of center-
stage converts the signal output of the audio oscillator
tapped inductance L2, trimmer capacitors C18 and C19,
into a visual indication of the frequency deviation
split-stator main tuning capacitor C16A and C161, and
contained in the signal generator output signal. The
capacitor C17.
The in-phase feed-back voltage
amount of frequency deviation is read from
necessary to sustain oscillation is coupled by C15 to the
KILOCYCLES DEVIATION meter M1, a direct-current
grid of V5. Assume that a positive signal voltage
(de) microammeter calibrated in kilocycles.
This
appears at the grid of V5. After amplification by V5, the
reading, when multiplied by the setting of the DEV
signal voltage with respect to ground is negative at the
MULT switch (X1, X5, or X10), is the amount of
plate side of L2 and positive at the grid side. This is
frequency deviation.
because the junction of tuning capacitor C16A and
C16B is connected to ground. The signal voltage across
i. Deviation Multiplier The deviation multiplier is
.
C16A and the lower half of L2 is, therefore, of the proper
a resistive attenuator which controls the amplitude of the
polarity to reinforce the existing signal voltage at the
audio voltage that is fed to the modulator. The amount
grid of V5. The amount of feed-back voltage coupled to
of attenuation is controlled by the DEV MULT switch.
the grid circuit is determined by the ratio of capacitance
j. Modulato. This stage consists of amplifier V10,
r
between the grid side to ground and from the plate side
modulator V11, and saturable reactor L1. The audio
to ground in the
signal
from
the
deviation
multiplier
23
