Explain the operation of Hartley oscillator and state its application.

Hartley Oscillator:

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$R_1,R_2$ and $R_C→$ Resistances for biasing of transistors.

$C_{c1}$ and $C_{c2}→$ Coupling capacitors $C_C→$ bypasses $R_e$. The feedback circuit is formed by components $L_1,L_2$ and $L_s$

The amp is $C_e$ configuration, Hence it provides 180 degree phase shift between its i/p / o/p . The feedback circuit provides an additional 180 degree phase shift to satisfy the condition for the + ve feedback.

The frequency. of oscillation: EQUATION

$(L_1+L_2 )→$ Equivalent inductances. EQUATION

Non-considered mutual inductances between $L_1$ and $L_2$ . Inductors $L_1$ and $L_2$ (in practice) are wound on the same core so we can’t neglect the mutual inductance M present between them. So, considering mutual inductance, eq ind. $L_{eq}$ is $L_1+L_2+2M$

The oscillator frequency. can be varied by varying the capacitor EQUATION. The frequency variation over a wide range can be easily obtained.


  • Easy to tune
  • It can operate over a wide frequency. range typically from few Hz to several MHz.
  • Easy to change the frequency. by means of a variable capacitor.


  • Poor frequency. stability.


  • Used as local oscillator in radio/tv recievers.
  • In function generators.
  • In RF sources.
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