05-01-2013, 03:24 PM
Hartley Oscillators
[attachment=46571]
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/(2π(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.
[attachment=46571]
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/(2π(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.