Figure 9. R oscillator circuit.
f
and V4 and applies it to saturable reactor L1 which, in
tuned circuit. Capacitor C17 balances the distributed
turn, frequency-modulates the output signal of the rf
shunt capacitance introduced into the tank circuit by
oscillator. The control winding of L1 is connected in a
output coupling capacitor C21.
voltage divider circuit which includes potentiometers
b. The output frequency is changed by varying the
R65, R66, and R100, and temperature compensating
capacitance of C16A and C16B. This capacitor is linked
resistor RT2. The signal winding of L1 is connected
mechanically to the manually adjusted front-panel
across a portion of oscillator tank coil L2. The control
TUNING control. Trimmer capacitors C18 and C19 are
and signal windings are arranged so that a negligible
used to adjust the high-frequency (50 mc) end of the
amount of mutual inductance 3A exist between
oscillator tuning range. The low-frequency end of the
windings. Consequently, energy is not transferred from
tuning range is adjusted by changing the position of the
one winding to the other. However, the permeability of
powdered iron cores in each end of tank coil L2. Plate
the core material, which is common to both windings,
voltage for V5 is obtained from the 150-volt regulated
changes with variations in the amplitude of current
supply. Grid leak bias is developed across resistor R39.
flowing in the control winding. The steady dc bias
A decoupling filter, consisting of resistor R40 and
current, which is set by bias potentiometer R100 and
capacitor C20, prevents rf energy from entering the B+
which flows through the control winding of L1, reduces
supply line.
the permeability of the core to a predetermined point.
The amplified audio-frequency output of V10 and V11
c. The oscillator circuit is frequency-modulated by
coupled through C52 is superimposed upon the de bias
changing the effective inductance of the tuned circuit.
and varies the permeability of the core material about a
The two, taps on tank coil L2 are connected to the signal
predetermined point. As the current through the control
winding of saturable reactor L1. Any variations in the
winding increases, the permeability of the core material
inductance of the reactor produce a corresponding shift
decreases, thereby decreasing the inductance of the
in oscillator frequency. A more detailed description of
signal winding. Since the signal winding is connected
the function of this reactor is contained in paragraph 43.
across a portion of oscillator tank coil L2, the effective
inductance of the oscillator circuit is reduced and the
43. Modulator V10 and V11
frequency of oscillation is increased. Conversely, a
decrease in current
of two triode connected type 5654 pentodes, amplifies
the
output
signal
of
audio
oscillator
V3
24
