Hartly oscilattor

OBJECTIVES: To study and calculate frequency of oscillations of Hartley oscillator. Compare the frequency of oscillations, theoretically and practically.


Transistor    BC 107 -1 No.

Capacitors   0.1µF, 10 µF -1 No. each

                       0.22 µF -2 Nos

Resistors     47Kohms, 1Kohms and 10Kohms -1 No.

Decade inductance box (DIB) -1 No.

Decade resistance box (DRB) -1 No.

Inductors : 5mH – 2 Nos.

CRO(Dual Channel ) (0-20 MHz)

Function generator ( 1Hz to 1 MHz)

Regulated power supply (0-30V)

Bread board

Connecting wires


Hartley oscillator is very popular and is commonly used as a local oscillator in radio receivers. It has two main advantages viz… Adaptability to wide range of frequencies and easy to tune. The tank circuit is made up of L1, L2, and C1. The coil L1 is inductively coupled to coil L2, the combination of two functions acts as auto transformer. The resistances R2 and R3 provide the necessary biasing. The capacitance C2 blocks the d.c component. The frequency of oscillations is determined by the values of L1, L2 and C1 and is given by,


The energy supplied to the tank circuit is of correct phase. The auto transformer ( L1 and L2 forms as an auto transformer) provides 180o out of phase. Also another 180o is produced by the transistor. In this way, energy feedback to the tank circuit is in phase with the generated oscillations



1. Connections are to be made as per the circuit diagram properly (C1 value to be selected as 0.1µF and10µF as required).

2. Connect CRO at output terminals and observe the wave form.

3. Calculate practically the frequency of oscillations by using the expression.

f=1/T, Where T= Time period of the waveform

4. Repeat the above steps 2, 3 for different values of L1 and note down practical values of oscillations of Hartley oscillator.

5. Compare the values of frequency of oscillations both theoretically and Practically.



Theoretical frequency


Practical frequency





  1. All the connections are to be connected properly.
  2. Transistor terminals must be identified properly.
  3. Reading should be taken without any parallax error.

RESULT: Frequency of oscillations is calculated and compared with theoretical values.


Students are able to Design and analyze Hartley oscillator

Viva questions:

  1. What are the applications of LC oscillator?
  2. What type of feedback is used in oscillators?
  3. What is the loop gain of an oscillator?
  4. What is the difference between amplifier and oscillator?
  5. What is the condition for oscillations?