Hartley Oscillator: What is it? Working and Its Applications


The Hartley oscillator is a one of the type of oscillator which consists of two inductive coils in series with capacitor. This circuit produces uncontrollable amplitude of oscillations. This oscillator was invention by American engineer Ralph Hartley, in 1915. This is harmonic type oscillator. It is use in commendation system. Hartley oscillator is not same as a tune collector oscillator. In this article we will discuss about of what are Hartley oscillator and it’s working.

What is a Hartley Oscillator?

The Hartley oscillator is a type of oscillator. Those are two inductive coils in series with a parallel capacitor to form its resonance tank circuit producing sinusoidal wave. A Hartley oscillator is harmonic type oscillators. The oscillation frequency is determined by an LC oscillators. It is typically tuned to produce waves in the radiofrequency band, which is why they are also known as RF oscillators.


The frequency  is determined by LC tank circuit which is shown in above figure. In LC tank circuit the inductor is in series and the capacitor is connected across them in parallel. It is mostly use in radio frequency (RF) oscillator applications and the recommended frequency range is from 20 KHz to 30 MHz it can be also use in below 20 KHz frequency but at lower frequency the inductors value should be high and it has a practical limit.

Basic Hartley Oscillator Design and Working

The circuit diagram is shown below. In this circuit contain common emitter configuration resistor and tank circuit. Here the RC is a collector resistor while RE is emitter resistor to form stabilization. The resistor R1 and R2 are use for voltage divider biasing network for transistor in common emitter configuration.


Hartley Oscillator

The capacitor Ci and Co are bock the DC voltage at the input and output side while CE are emitter capacitor, that are use for bypass amplifier AC signal all the element are shown in figure.

Now let us discuss working of Hartley oscillators, first switch ON the power supply, the transistor starts to conduct and the collector current IC increases. The collector current charge the capacitor C. when the capacitor are fully charge it starts discharging via inductors L1 and L2. This process will continue. This charging and discharging result produce the damped oscillations in the tank circuit.

The oscillating current produces across inductors inductors L1 and L2 which are out of phase by 180.

From the figure, the output of amplifier is applied to L1 while the feedback voltage drown L2 is applied to the input of base. The amplifier produce 180 degree of phase shift and tank circuit also produce 180 degree phase shift, thus the total phase shift of amplifier is 360 or 0 degree.

Frequency of Oscillations in Hartley Oscillator

The frequency of oscillations of Hartley oscillators is circuit is given as


But in Hartley oscillator, we consider two inductors in the tank circuit thus equivalent inductance will be given as

Leq = L1 + L2

The mutual inductance between the coils must be consider for calculation of equivalent inductance,

Leq = L1 + L2 + 2M

Thus the oscillating frequency is given as



The advantages are listed below,

  • It required very less components
  • The frequency of oscillator is change by varying the inductors and capacitor value.
  • Circuit is very simple
  • The sinusoidal oscillations with constant amplitude are produces by Hartley.


The disadvantages of Hartley oscillator are given below,

  • It is not use for low frequency at low frequency the value of inductor and size of inductor is large
  • Sometime it produces distortion in sinusoidal signal due to the presence of harmonics. It is a major drawback.


The applications of Hartley oscillator is discussed below,

  • It is use in radio frequency as a local oscillator, because it works on wide range of frequency.
  • It is use for generating sinusoidal wave at desire frequency.
  • It is suitable for radio frequency range up to 30 MHz

People also ask

What is Hartley oscillator used for?

It is an electron circuit that are use to generate sinusoidal with constant amplitude. It is use in radio frequency as a local oscillator.

What is the principle of Hartley oscillator?

It is made of two inductors and one capacitor. The principle of Hartley oscillators is based on charging and discharging of LC circuit.

What is oscillator Hartley oscillator?

It is an electronics circuit that generate sinusoidal wave. Frequency of this oscillator is determine by tune circuit consist of two inductors and one capacitor.

What is the frequency of Hartley oscillator?

20 kHz to 30 MHz

It is mostly use in radio frequency (RF). The frequencies lie in between 20 kHz to 30 MHz. it can be operate at low frequency but it required high value of inductor and it has a practical limit.

Where is Hartley oscillator commonly used?

Radio frequency (RF)
It is mostly use in radio frequency. The range of radio frequency is 20 kHz to 30 MHz.

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