TM 11-6625-486-14&P
Capacitor C701A, connected to the collector of Q101, is
5-3. Low Frequency Oscillator Circuit
the main TUNING capacitor which is used to tune each
coil over its range.
Capacitor C702A is labeled
CORRECTOR on the front panel and enables the
operator to bring the oscillator to its correct frequency.
transistorized, is the vfo used for ranges A and B. It
Fixed capacitor C705 acts as a series padder for C702A.
consists of a tunable oscillator stage Q101 and buffer
Trimmer capacitors C112 and C114 adjust vfo tracking at
amplifier Q102. The oscillator produces fundamental
the high end of the ranges. The primary inductance of
frequencies that may be varied from 125 to 250 kHz in
L102 is adjusted for low end tracking by a slug. Low end
range A, and 2,500 to 5,000 kHz (5 MHz) in range B.
tracking of L103 is preset during manufacture. Capacitors
Harmonics extend up to 2.5 MHz in range A, and 65 MHz
C108 and C109 provide emitter coupling for the feedback
in range B.
The filmstrip is calibrated directly in
signals. Resistor R112 decreases the feedback signal in
fundamentals for range A (125 to 250 kHz), and range B
range A. Tank circuit bypass capacitors C104 and C110
(2,500 to 5,000 kHz). A mask, operated by the RANGE
have similar functions.
These two capacitors are
SW, covers all filmstrip ranges except the range in use.
necessary because of lead length inductance between
decoupling resistor R106 and the tank circuit. These
b. The oscillator circuit of Q101. is the transistor
capacitors keep rf out of the power supply in addition to
counterpart of a vacuum-tube tickler feedback oscillator.
preventing 900-hertz modulating voltage from being
The positive feedback signal is obtained between the
applied to the oscillator.
collector and emitter through the primary and secondary
windings of coils L102 and L103. One section of RANGE
c. The emitter of Q101 is terminated by R103 which
SW S703 switches the collector of Q101 to the
appropriate primary winding, and the other section of
feedback windings. Resistor R101 and CR101 from a
S703 switches the emitter to the proper feedback winding.
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