2018-01-08 RF Oscillator For AM Band

For FB group Building Transistor Radios
When I started building regen receivers, the first thing I found I needed was a simple  signal generator.  I have a function generator, but every time I want a different frequency, I had to readjust the controls.  So I built a few RF oscillators to put close to the receiver so I can adjust the receiver.  This is one of them.  They need only a single transistor, a few other parts, and a coil that I made out of a pill bottle and some telephone wire.

All of the important parts are visible.  The .22 uF power supply bypass capacitor is hidden under the black tape to the left.

The two blue capacitors are 2.2 nF.  The windings under the tape are enough to make 75 microhenrys.  This inductance along with the two blue caps resonate at 560 kHz., the low end of the AM band.  Less inductance and/or capacitance gives a higher frequency.  The .22 uF red capacitor blocks the base bias from going through the coil.  The 470 ohm (yellow, violet, brown) resistor is the emitter load resistor.  The 39k (orange, white, orange) is the base bias resistor.  The collector and base bias resistor are connected to the positive 5 to 6 volts.  

The supply voltage can be modulated by putting a transformer in series with the supply.

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