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AEC LAB MANUAŁ

HARTLEY OSCILLATOR

AIM: Testing for the performance of BJT Haiiley oscillator for f_o=l()0KH/.

COMPONENTS REQUIRED:

SLNo	Components	Rangę	Quantitv
1	TransLstor	SL-100	1
2	Resistors	22K.2.2K.4.7KJK.470a 1K POT	1
3	Capacitors	0.47p F.47pF	0.47 pF =2 47 pF=l
4	Variable power supply	(0-30) V	1
5	DSO	-	1
6	Function Generaator	-	1
7	Connecting wires	-	1 set
8	Decade Iitduc tance box	_	1
9	Decade Capacitane box	-	1

THEORY:

When the collector supply voltage Vcc is switched on. collector current starts rising and charges the capacitor C. When this capacitor is fully charged. it discharges thiough coiLs LI and L2, setting up damped harmonie ascillations in the tank Circuit. Ihe oscillatory current in Ute tank Circuit produces an a.c. voltage acrass LI which is applied to Ute base emitter junction of Ute transistor and appears in the amplified form in Ute collector Circuit.

Feedback of energy front output (collector emitter circuit) to input (base-emitter Circuit is) accomplished Utrough auto transformer action. The output of the amplifier is applied acrass Ute inductor LI. and Ute voltąge acrass L2 forms the feedback voltage. Thecoil LI. Ls inductively coupled to coil L2. and Uiecombination acts as an auto-transformer.

ThLs energy supplied to the tank circuit overcomes Ute lasses occurring in it. Consequently Ute ascillations are sustained in the circuit. Ihe energy supplied to Ute tank circuit Ls in phase with the generated ascillations. The phase difference between the vohages acrass LI and Utat acrass L2 Ls always 180° because the centre of Ute two is grounded. A furUter phase of 180° Ls introduced between Ute input and output voltages by the transLstor itself. Thus Ute total phase shift becomes 360° (or zero), Utereby making the feedback positive or regenerative which is essential for oscillations.

Dept. of ECE, KSSEM Page 30