MINI FM TRANSMITTER
A mini project report
By
R131835 : B SIREESH BHUSHAN CHOWDRAY
R131743 : G RAJESH
R131281 : SWARNA KARTHIK
R131912 : T HARI KRISHNA
Under the guidance of
Ms. G. Lakshmi Shireesha
Lecturer, Dept. of ECE
Rajiv Gandhi University of Knowledge Technologies,
RK Valley, Kadapa
Department of Electronics and Communication Engineering
Rajiv Gandhi University of Knowledge Technologies,
Department of Electronics and Communication Engineering
Rajiv Gandhi University of Knowledge Technologies,
RK Valley, Kadapa, AP, 516329
CERTIFICATE
This is to certify that this work entitled “ MINI FM TRANSMITTER”
was successfully carried out by T. Mr. B SIREESH,G RAJESH, T HARI
KRISHNA,SWARNA KARTHIK, in partial fulfillment of the
requirements leading to award the credits for mini project in
ELECTRONICS AND COMMUNICATIONS ENGINEERING by
RAJIV GANDHI UNIVERSITY OF KNOWLEDGE
TECHNOLOGIES, RK VALLEY During the academic year
2017-2018.
Internal Guide ,
Ms. G Lakshmi Shireesha
Lecturer,
Department of ECE,
RGUKT, RK VALLEY.
INDEX
I. Abstract
II. Introduction
III FM Theory
IV. Components Explanation
V. Block Diagram of FM Transmitter
VI. Circuit Explanation
VII. Advantages
VIII. Disadvantages
IX. Conclusion
MINI FM TRANSMITTER
Abstract :
The aim of the project is to
develop a Miniaturized low power FM Transmitter to be used in
specialized applications such as a hearing aid for a tour guiding system .
The overall module should be miniature to enable portability. Frequency
modulation has several advantages over the system of amplitude
modulation (AM) used in the alternate form of radio broadcasting.
The most important of these
advantages is that an FM system has greater freedom from interference
and static. Various electrical disturbances, such as those caused by
thunderstorms and car ignition systems, create amplitude modulated radio
signals that are received as noise by AM receivers. A well-designed FM
receiver is not sensitive to such disturbances when it is tuned to an FM
signal of sufficient strength. Also, the signal-to-noise ratio in an FM
system is much higher than that of an AM system. FM
broadcasting stations can be operated in the very-high-frequency bands at
which AM
interfacing is frequently severe; commercial FM radio stations are
assigned
frequencies between 88 and 108 MHz and will be the intended frequency
range of
transmission.
Introduction
Objective:
The primary purpose of the project is to understand the operation of the
basic wireless telecommunication. By going through the project , theoretical
knowledge is preferred into practice .During the hardware implementation
,practical skills such as soldering , printed circuit board implementation and
circuit testing can be enhanced
FM THEORY
Angle and Amplitude Modulation are techniques used in
Communication to transmit Data or Voice over a particular medium, whether it be
over wire cable, fibre optic or air (the atmosphere). A wave that is proportional to the
original baseband (a real time property, such as amplitude) information is used to vary
the angle or amplitude of a higher frequency wave (the carrier).
Carrier=Α Cos Φ (t)
φ (t) = 2 π f C t+ α
Where A is the amplitude of the carrier and φ(t) is the angle of the carrier, which
constitutes the frequency (f C ) and the phase (α) of the carrier. Angle modulation
varies the angle of the carrier by an amount proportional to the information signal.
Angle modulation can be broken into 2 distinct categories, frequency modulation and
phase modulation. Formal definitions are given below :
Phase Modulation (PM) : angle modulation in which the phase of a carrier is
caused to depart from its reference value by an amount proportional to the modulating
signal amplitude.
Frequency Modulation (FM): angle modulation in which the instantaneous
frequency of a sine wave carrier is caused to depart from the carrier frequency by an
amount proportional to the instantaneous value of the modulator or intelligence wave.
Phase modulation differs from Frequency modulation in one important way. Take a
carrier of the form A Cos(ω C t + θ) = Re{A.e j(ωCt + θ) }
Pm will have the carrier phasor in between the + and - excursions of the modulating
signal. Fm modulation also has the carrier in the middle but the fact that when you
integrate the modulating signal and put it through a phase modulator you get fm, and
ifthe modulating wave were put through a differentiator before a frequency modulator
you get a phase modulated wave. This may seem confusing at this point, but the
above concept will be reinforced further in the sections to follow.
Derivation of the FM voltage equation:
Consider a voltage controlled oscillator with a free running frequency of f C , an
independent voltage source with voltage V M (t) which causes the VCO to depart
from f C by an amount ∆f, which is equal to the voltage of the independent source
multiplied by the sensitivity of the VCO (K O => such as the miller capacitance of a
transistor).What is seen at the output of the VCO is a frequency modulated voltage.
Now consider the independent voltage source as representing the amplitude of the
baseband information .
Above are the equations which govern the output of the VCO, f is the overall
frequency of the frequency modulated output.
taking the angle θ(t) from equation 1 and differentiating it will give the angular
velocity of the output and equate it to 2π times the effective frequency (f)
multiply across both sides by the change in time (dt)
Substituting in the equation for the intelligence (baseband) voltage 7 into equation 6
and integrating gives equation 8 which is the angle of the frequency modulated wave
of
equation 1.
Tiding up equation 8, and setting the magnitude of the sine wave as M F , the
modulation index for frequency modulation.
The above equation represents the standard equation for frequency modulation.
The equation for the other form of angle modulation, phase modulation is rather
similar but has a few subtle differences.
The difference is in the modulation Index and the phase of the varying angle inside
the
main brackets.
Technical terms associated with FM
Now that Fm has been established as a scheme of high quality baseband
transmission, some of the general properties of FM will be looked at.
Capture Effect
Simply put means that if 2 stations or more are transmitting at near the
same frequency.FM has the ability t pick up the stronger signal and attenuated the
unwanted signal pickup.
(Was known as the modulation factor)
Modulation Index is used in communications as a measure of the relative amount of
information to carrier amplitude in the modulated signal. It is also used to determine
the spectral power distribution of the modulated wave. This can be seen in
conjunction with the Bessel function. The higher the modulation index the more
side-bands are created and therefore the more bandwidth is needed to capture most of
the baseband’s
information.
Deviation Ratio
The deviation can be quantified as the largest allowable modulation index.
For the commercial bandwidth the maximum carrier deviation is 75KHz. The human
ear can pick up on frequencies from 20Hz to 20KHz, but frequencies above 15KHz
can be ignored, so for commercial broadcasting (with a maximum baseband frequency
of 15KHz) the deviation ratio is 5 radians
.
Carrier Swing
The carrier swing is twice the instantaneous deviation from the carrier frequency.
The frequency swing in theory can be anything from 0Hz to 150KHz.
Percentage Modulation
The % modulation is a factor describing the ratio of instantaneous carrier deviation to
the maximum carrier deviation.
Carson’s Rule
Carson’s Rule gives an indication to the type of Bandwidth generated by an FM
transmitter or the bandwidth needed by a receiver to recover the modulated signal.
Carson’s Rule states that the bandwidth in Hz is twice the sum of the maximum
carrier
frequency deviation and the instantaneous frequency of the baseband.
REQUIRED COMPONENTS
1.RESISTORS(10K,1M,100K,1K)
2.CAPACITORS(0.1uF,0.01uF,4.5uF)
3.TRIMMER CAPACITOR(40pF)
4.AUDIO JACK
5.BATTERY (9V)
6 BATTERY CLIP
7.PCB
BLOCK DIAGRAM
CIRCUIT EXPLANATION
Circuit Operation:
This circuit is used as an FM transmitter. In this there are 3 stages . In
first stage we take input in second stage we amplify input and finally in
third stage we frequency modulate the signal and transmit it through
antenna.
First stage:
In this we give voice through microphone or song through audio jack.
This circuit takes 9v as supply voltage .
Resistor R1 ;
As we are using microphone here it does not need 9V and also it may
damage due to high voltage. So to avoid this we use resistor R1. This
resistor is used to divide voltage . When we connect R1 and microphone
in series then microphone takes the desired voltage and rest of the
voltage is dissipated across R1.;
Capacitor C1 :
This is coupling capacitor. This is capacitor is used to block DC
voltage. Capacitor is frequency dependent.
1
Resistance across capacitor is =
j 2fC1
So for DC frequency (f) is equal to 0 . Now capacitor becomes open
circuit and not signal flows.So this capacitor blocks DC voltage.
Second Stage:
In this stage we amplify the input signal because the input from
microphone is in very low amplitude.This amplifier circuit is in self bias
mode.
Resistors R3,R4,R5,R6 :
In our circuit R3=R1 , R4=R2 ,R5=Rc ,R6 = Re corresponding to below
circuit.
Self Bias Circuit :
It is also called Voltage Divider Bias Circuit. This is the best amplifier
configuration .It has more stability than others.
DC Analysis:
Voltage from base to ground is
R2VCC
Eth = = VR 2
R1 R2
ETh VBE
IB
RTh ( 1) RE
VCE VCC I C ( RC RE )
VE
IE
RE
Our circuit values :
ETh =
IB =
VCE =
IE =
AC Analysis :
R1R2
R ' R1 || R2
R1 R2
26mv
re
IE
Input Impedance =
Z i R ' || re
Z o RC || ro
Output Impedance =
Vo RC || rO
AV
Gain =
Vi re
From data sheet :
r o hoe 106
h fe 100
Our Circuit Values
Input Impedance =
Output Impedance =
Gain =
Third Stage :
In this stage Frequency modulation is done and it is send through
antenna.
Tank Circuit :
This circuit is used to generate the required frequency. C4 and L1 are
used to oscillate tank circuit at certain frequency.C4 and L1 are selected
according to frequency to which we want to make oscillations.In this we
selected inductance and according to it capacitance is calculated.
d 2n2
L
18d 40l In micro Henre
Where
d=Diameter of coil.
n = Number of turns.
l = Length of coil.
1
f
2 L1C4
f = FM frequency
At HIgh Frequency :
At High Frequency transistor internal capacitances comes into
action. Internal capacitances are very low value so they are open
circuit . At high frequency they come into action and changes the
capacitance according to voltage. Since input changes so
capacitances also changes.So this changes total capacitance of
tank circuit .This change in frequency in tank circuit changes
frequency according to input and totally input signal is frequency
modulated.
Capacitance C5:
The Capacitance C5 is used as feedback capacitor.
ADVANTAGES
This transmitter will reject the noise signal from an amplitude
variation
It is very useful in educational purposes like providing
information in university fests
The FM transmitters are easy to use and the price is low The
efficiency of the transmitter is very high
DISADVANTAGES
This has a limited range of transmitting over area
Distortion of noise
CONCLUSION
The fundamental idea of this project is to low powered FM
transmitter, multichannel FM transmitter for modulation across
the commercial band.
