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EXPERIMENT NO.1

Hartley oscillator

AIM :To build Hartley oscillator circuit, measure its frequency of oscillation and compare it

with the theoretical value.

APPARATUS :

1) D.C regulated power supply 0-30v, 2A, 1No.

2) Digital Voltmeter , 1No.

3) CRO,dual trace ,1 No.

4) Bread board.

5)

Connecting wire.

COMOPNENT :

1) Transistor: BC107 or 2N3903 or 2N3904 or equivalent,1No.

2) Carbon resistor: each 1/2W, 1 No each 27k, 2.7k, 1.2k, 120k.

3) Capacitor: 0.1F, 2 no, 0.015F 1 No., 3.3F, 1 No.

4) Inductor: 200H, 1 No., 100H 1 No.

CIRCUIT

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THEORY :

Circuit of a Hartley oscillator is shown in figure. Q is an NPN type transistor. R1and

R2are the biasing resistors. REis the resistance connected in the emitter circuit for bias

stabilization. CE is the bypass capacitor. Oscillator energy is coupled to the tank circuit

formed by the two inductors L1,L2 and capacitor C. It decides the frequency of oscillation.

. Rc is the resistance in the collector circuit.Cc1 is the input coupling capacitor through

which the voltage developed at output is coupled to the base via tank circuit. Tank circuit

gives a phase shift of 180 degree ,so the positive feedback is given to input. This

capacitor also prevents DC entering in to the tank circuit from the base. Cc2 is the output

coupling capacitor. Oscillation energy is coupled to the tank circuit by this capacitor this

capacitor also blokes d.c. entering the tank circuit. This is necessary because otherwise

the Q factor of the tank circuit is reduced. Output is taken as shown.

Frequency of oscillator is given by f

Where L = L1+ L2

If L is in henry , C is in Farad ,f will be in Hz

PROCEDURE :

1) Prepare CRO for operation.

2) Connect the circuit as shown in the circuit diagram.

3) Apply +Vcc = 9V from the power supply.

4) Connect the CRO probes across the output terminals.

5) Obtain the waveform on the screen.

6)

Measure the time period T of one complete wave and calculate the frequency ofoscillation. f=1/T hz , where T is in second

7) Calculate the theoretical value of the frequency of oscillation, f

8) Compare Meadured ( Actual frequency ) with theoretical value of the frequency

9) Switch off the supply.

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OBSERVATION TABLE :

Time

period T

Frequency

Measured f= Calculated f

CALULATION : L = L1+ L2 : =

C =

f

CONCLUSION :