Where,
R1 and R2 = Potential
divider bias
RE = Emitter Resistance
RFC = Radio Frequency Choke
Cc = Coupling Capacitor
CE = Emitter Bypass Capacitor
The above
figure shows the circuit of the ‘CE’ transistorized Hartley
oscillator. Its tank circuit consists of two inductors L1 and L2
these inductors are connected in series with and parallel with a capacitor ‘C’.
The coil L1
is inductively coupled to coil L2 and the combination works as an auto-transformer.
The Hartley
oscillator is widely used as local oscillators in radio receiver’s and etc…
CIRCUIT
OPERATION:
When the
power supply is given to the circuit, the transistor starts conducting and
collector current increases as a result the capacitor starts charging. When the
capacitor is fully charged it starts discharging through coil L1. This charging
and discharging create undamped oscillations in the tank circuit.
The tank
circuit produces 1800 phase shift and transistor CE
amplifier itself produces another 1800 phase shift. Thus, a total
phase shift is 3600.
Hence, the
feedback is positive.
the
frequency oscillator is determined by the values of L1 and L2 and is given by:
f= 1/2π˥LC
where,
L=L1+L2+2M
M = Mutual
Inductance between L1 and L2
And its
units are Hertz (Hz).
Feedback
factor, β = XL2/XL1
=ωL2/ωL1
=L2/L1
The minimum value of amplifier gain to maintain oscillations
is
A β = 1
A = 1/ β
A = 1/(L2/L1)
A= L1/L2
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