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Here
is a versatile circuit of IF signal generator which may be of
interest to radio hobbyists and professionals alike.Transistors T1
and T2 form an astable multivibrator oscillating in the audio
frequency range of 1 to 2 kHz. RF oscillator is built around
transistor T3. Here again a 455kHz ceramic filter/resonator is
employed for obtaining stable IF. The AF from multivibrator is
coupled from collector of transistor T2 to emitter of transistor
T3 through capacitor C3. The tank circuit at collector of
transistor T3 is formed using medium wave oscillator coil of
transistor radio, a fixed 100pF capacitor C5 and half section of a
gang capacitor (C6).
The oscillator section may be easily modified for any other
intermediate frequency by using ceramic filter or resonator of
that frequency and by making appropriate changes in the tank
circuit at collector of transistor T3. Slight adjustment of bias
can be affected by varying values of resistors R6 and R7, if
required
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