The LC tank circuit receives pulses of collector current and begins to resonate at its designed frequency.
A Hartley oscillator can be implemented by using an operational amplifier and its typical arrangement is shown in figure below. As the capacitor is fully discharged the magnetic field starts decreasing.
The amplitude of the signal produced will depend on the amount of current flowing in the LC tuned circuit. Dispatches from Pluto: Because most of the current flowing in the oscillator is flowing just around the resonant tank circuit rather than though the amplifier section of the oscillator, LC oscillators generally produce a sine wave with very little amplifier sourced distortion.
R 1 and R 2 form a potential divider across Vcc.
The operation of this circuit is similar to the transistor version of Hartley oscillator. In this variation however, rather than using a tuned amplifier that amplifies only at the desired frequency, the amplifier here will operate over a wide range of frequencies. In practice the core shared by such a tapped inductor working at RF frequencies will often be found to be a variable type as shown in Fig.
Smart People Should Build Things: Devil in the Grove: Capacitors CC1 and CC2 are the coupling capacitors. Now the transistor comes into the picture. When the supply is switched—on, a voltage V 1 is developed across L 1 and V 2 across L 2.
Mutual inductance is an additional effective amount of inductance caused by the magnetic field created around one inductor or one part of a tapped inductor inducing a current into the other inductor.
This ensures that the fraction of the output signal fed back from the tuned circuit collector load to the emitter via the capacitor C2 provides the necessary positive feedback. This Changes Everything: The Unwinding: Hartley oscillators are commonly used in radio frequency RF oscillator applications and the recommended frequency range is from 20KHz to 30MHz. Since the amplifier is in CE configuration, it produces a phase difference of 180 0.
An NPN transistor connected in common emitter configuration serves as active device in amplifier stage. In practical, a common core is used for both inductors, however depending on the coefficient of coupling the mutual inductance effect can be much greater.
This gives rise to an electric field across the capacitor plates in the direction shown. When the capacitor attains full charge it discharges through inductor L1 and L2.Animation shows working principle of hartley oscillator