Hartley Oscillator:

Operation:

$R_1,R_2$ 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.

Advantages:

• 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.

Disadvantages:

• Poor frequency. stability.

Applications:

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