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Wednesday, October 5, 2011

HARTLEY OSCILLATOR Electronic devices and circuits lab manual


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

APPARATUS:      Transistor BC 107
                              Capacitors 0.1μF, 10 μF
                              Resistors 6.8Kohm, 1Kohm and 100Kohm
                              Decade inductance box (DIB)
                               Decade resistance box (DRB)
                               Cathode ray oscilloscope
                               Bread board
                               Regulated power supply (0-30V)
                               Connecting wires
CIRCUIT DIAGRAM:



THEORY:
                   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 functions 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,

                              F=1/(2p(C1(√L1+L2)))

The energy supplied to the tank circuit is of correct phase. The auto transformer provides 180˚ out of phase. Also another 180˚ is produced
By the transistor. In this way, energy feedback to the tank circuit is in phase with the generated oscillations.

PROCEDURE:
   1. Connections are made as per the circuit diagram.
   2. Connect CRO at output terminals and observe 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 colpitts oscillator.   
 5. Compare the values of frequency of oscillations both theoretically  
          And Practically.




OBSERVATIONS:

CAPACITANCE(μF)
Theoritical frequency
                 (KHZ)
Practical frequency
        (KHZ)





MODEL GRAPH:



PRECAUTIONS:
1.    All the connections should be correct.
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.

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