Oscillators

1. Tuned circuits in FM trans receiver
EXPERIMENT NO :4
AUGUST 2, 2017
MIT ACADEMY OF ENGINEERING, DEPARTMENT OF ENTC ENGG
ANALOG ELECTRONICS PRACTCAL JOURNAL
Batch B1 Bock 1
Omkar Rane SETB118
Rohit Mane SETB102
Abhishek Sainkar SETB104
Tanmay Kale SETB112

2. S.Y.B. Tech (ET): 2017-18 Analog Electronics
EXPERIMENT No: 4
Tuned circuits in FM trans receiver
Introduction:-
FM transmitter is uses FM waves for transmitting the sound. It transmits
the audio signals through the carrier wave by the difference of frequency.
The carrier wave frequency is equivalent to the audio signal of the
amplitude and the FM transmitter produce VHF band of 88 to 108MHZ.
A FM receiver uses frequency mixing a received signal to a fixed
intermediate frequency. Virtually all modern radio and television receivers
use the super heterodyne principle. Usually a radio receiver operates with
an intermediate frequency of 10.7MHz. In order to mix down the received
frequency to the IF, the local oscillator should work between 98.7MHz and
118.7MHz

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Fig.1 Block diagram of FM trans receiver
At the heart of an FM transmitter is a set of LC Oscillator. An LC oscillator
uses an inductor and a capacitor to oscillate electricity (and a magnetic
field). It works by converting the stored magnetic energy through an
inductor coil into electrical energy and then storing this energy in a
capacitor. After some time, the decaying magnetic field stops supplying an
electro motive force and the energy from the capacitor was then discharged
into the circuit and converted into magnetic energy through the inductor.
This cycle of ever changing energy state is the basis of an oscillator.
Objective: -
 To implement different types of tuned circuits
 To calculate frequency of oscillation
Pre-lab Questions: -
Identify the Oscillator circuit used in the transmitter circuit shown
below
Fig. 2 Circuit diagram of Voice transmitter

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Answer: This is the oscillator circuit in the above given circuit.
Lab Exercise: -
1. Circuit diagram of LC tuned circuits
(Hartley and Colpitts oscillator)
Fig 1 Hartley Oscillator
Fig 2 Colpitts Oscillator

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2. Procedure: - (Write in your own words)
1)Using multisim software make a Hartley, Colpitts and RC phase shift
oscillator circuit.
2)Using marker tool measure Vp-p peak to peak voltages from Vo (Output
voltage), Vf (feedback voltage), Vin (Input voltage) and also measure
frequency value at output voltage terminal.
3) Calculate theoretical value of frequency, A voltage gain, feedback factor
β,
(COLPITTS OSCILLATOR): -
a) Fosc = 1/2π√LCT
b) CT =
𝐶1 𝑋 𝐶2
𝐶1+𝐶2
c) Feedback fraction β =
𝐶1
𝐶2
(HARTLEY OSCILLATOR): -
a) Fosc = 1/2π√LCT
b) LT = L1+L2+M
c) Feedback fraction β =
𝐿1
𝐿2
4) For All cases verify Barkhausen Stability criteria as follows:
a) The frequency of oscillation at which sinusoidal oscillator
operates is the frequency for which the total shift introduced, as
the signal proceeds from the input terminals, through the
amplifier and feedback network, and back again to the input, is
precisely zero (or an integral multiple of 2*Π).
b) The loop gain is equal to unity in absolute magnitude, that is
|A*β|=1.

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3. List the Equipment’s / Component required for the experiment
Equipment / Components Specifications/Values
Function Generator CADDO,4061,3MHz Pulse
Generator with 40 MHz Frequency
Counter
CRO HAL-TEC plus, HT4030,30MHz,
Oscilloscope
Resistor R1=8k, R2=2.7k,RC=3.3k, RE=1k
Breadboard
Variable Power Supply Radial Industry SVP030002D
Transistor BC547{npn}
Inductor 3.9 µH, 430 µH, 13mH
Capacitor 100nF, 10nF,10µF
MULTISIM 12 0r 8 National Instruments.
4. Observation Table (Multisim readings)
Parameters Theoretical Practical
Fosc of circuit 1(Hartley
Oscillator)
122.346kHz 115 kHz
Fosc of circuit 2
(Colpitts Oscillator)
2.9760 kHz 4.029 kHz
Conclusion: -
We had simulated Hartley, Colpitts, RC phase shift oscillator on Multisim
software
We had also calculated theoretical and practical frequency of above
mentioned oscillators. We also verified that Barkhausen criteria for
stability of oscillators. We also came to know about that oscillator circuit
does not require any input signal to work. The signal is generated from
noise available in the components, further the output signal is amplified
(amplifier circuit) and feedback to input using feedback circuit. In this we

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get continuous oscillations.
Post Lab. Activity: -
In this experiment, you have implemented an LC oscillator using
transistor. There is another type of Oscillator called RC oscillator.
Implement any one type of RC oscillator on Multisim and Hardware and
attach your snapshots.
Note:- Kindly attach screenshot of your performed experiments
RC phase shift oscillator.
1. Each stage of RC produces 600 phase shift. Thus total phase shift is 1800.
2. Frequency of oscillation fosc = 1/2πRC√2N. N= no. of stages
3. Av = RF/R =29
4. Β = 1/29

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