A
PROJECT REPORT
ON
FM BUGGER
ABSTRACT
FM Transmitter is a device which generates frequency
modulated signal. It is one element of a radio system
which, with the aid of an antenna, propagates an
electromagnetic signal. Standard FM broadcasts are
based in the 88 108 MHz range.
These types of networks have applications in dynamic
spectrum access, co-existence of different wireless
networks, interference management, etc.
The main objective of this project is to transmit the
information from one person to another person in remote
location. Normally bugger is used for finding out the
status of the person like where is he is going, what he is
talking etc.
This circuit is mostly used in spy agencies. This is small
circuit with which we can listen to another people
conversation from long distance using the normal FM
radio set.
CHAPTER-1
INTRODUCTION
BACKGROUND
Frequency modulation (FM) is a technique for wireless
transmission of information where the frequency of a
high frequency carrier is changed in proportion to
message signal which contains the information according
to. FM was invented and developed by Edwin Armstrong
in the 1920s and 30s. Frequency modulation was
demonstrated to the Federal Communications
Commission (FCC) for the first time in 1940, and the
first commercial FM radio station began broadcasting in
1945. FM is not a new concept.
However, the concept of FM is essential to a wide gamut
of radio frequency wireless devices and is therefore
worth studying. This seminar will explain the design
decisions that should be made in the process of design
and construction of an FM transmitter. The design has
also been simulated. For a long time radio was the largest
mass media but in recent years it has lost a number of
listeners. In contrast, total media consumption has
increased.
Young people are abandoning traditional media and want
to decide on where, when and how they receive media
content, for example via Internet and mobile telephones.
Listeners are most interested in easily being able to select
radio stations, to have better sound quality and audibility
and to increase accessibility for people with visual and
auditory impairments. Listeners also want a wider range
of radio channels over the whole country. Consumers
needs must be met hence the need for advancements in
the field of radio broadcast.
New technology creates the necessary conditions for
improvements. This seminar also evaluates the different
technologies on the basis of questions like:
How well does the technology satisfy consumers
needs?
What functionality does the technology offer?
How efficiently does the technology utilize the
available spectrum?
What financial conditions are available for the
technology?
Standardization policy for the technology.
OBJECTIVES
The objectives of this project are:
To review present-day FM transmitters and their
limitations.
To provide an overview of the Radio
communication issues
To accusatively compare these technologies
SCOPE
This project covers the design of FM transmitters for
quality audio transmission and explains some of the
modern trends in FM signal generation, highlighting their
prospects. It also covers the advantages these
technologies offer over traditional radio broadcasting and
brings to light various distinguishing features possessed
by these technologies.
SIGNIFICANCE
The role that radio plays in the society is an important
issue to consider in discussions about which technology
can best distribute radio in the future. The fact that radio
has an important role in society can be clearly seen in the
number of listeners. Despite the rise in the total
consumption of media, radio has lost a number of
listeners according to a survey report. The medium of
radio has many positive characteristics for listeners. It is:
Free from subscription charges
Simple to use
Possible to listen to everywhere, including sparsely
populated areas and while in motion in cars and
trains
Possible to listen to while doing something else
Important as a channel of information, especially in
crises and catastrophes.
An important medium for traffic information,
shipping and mountain rescue.
CHAPTER-2
BLOCK DIAGRAM
AND
BLOCK DIAGRAM EXPLANATION
BLOCK DIAGRAM
Block Diagram of an Fm Transmitter
BLOCK DIAGRAM EXPLANATION
The diagram above is the basic building block of every
FM transmitter. It consists of an AF (Audio Frequency)
Amplifier that amplifies the audio voltage from the
microphone and feeds this signal into an RF oscillator for
modulation. The oscillator produces the carrier frequency
in the 88-108 MHZ FM band. The low power of the FM
modulated carrier is feeds into. A low pass filter is also
present lo limit the RF signal to a range of choice while
the antenna radiates it.
The design of an FM transmitter must consider multiple
technical factors such as frequency of operation, the
stability and purity of the resulting signal, the efficiency
of power use, and the power level required to meet the
system design objectives. Some pre-design
considerations include.
CHAPTER-3
CIRCUIT DIAGRAM
AND
CIRCUIT DIAGRAM EXPLANATION
CIRCUIT DIAGRAM:
FM Transmitter Circuit
COMPONENTS LIST
NO VALU E DESCR IPTIO N
R1 4.7k
R2 330
C1 1nF ceramic capacitor
NO VALU E DESCR IPTIO N
C2 10pF ceramic capacitor
C3 15pF ceramic capacitor
L 212nH 8 turns of 22 awg wire on a 6 mm drill bit
Q BC548 BC548 or equivalent like 2n3094 or bc547
Ant Spring Extension spring i stretched
Mic electret
microphone
Bat 3V 3V battery with its holder
CIRCUIT EXPLANATION
This spybug works by modulating a carrier frequency
with a modulating wave. the carrier frequency is
determined by the resonant circuit the inductor L and the
capacitor C3. In order to modulate that carrier frequency
there is a capacitor C2 and a transistor (which is
controlled by the mic) in series with the resonant circuit.
To understand it imagine that the transistor is fully off
(cut off region) then frequency is determined by LC3C2,
but if the transistor is fully on (saturation region)
the frequency is determined only by LC3, so the
frequency can be modulated up to LC3 and down to
LC3C2.
In this circuit our transistor is biased by R1,R2 and the
mic so we have the half of the power supply in its base
which is 1.5V, that means if the mic does not pick
up any sounds the frequency of the transmitter is
determined by LC3 and C2/2 because the transistor is
halfway on (active region). If the mic picks up a sound
(modulating wave) it varies the transistors bias thus the
frequency of the transmitter. thats how we get modulated
frequency in this circuit
CHAPTER-4
COMPONENTS DESCRIPTION
RESISTORS
Resistors can be of two types: fixed value resistors or
variable resistors. The formula for resistance is given by:
R = l / A where is resistivity, l is length and A is area
of crossection. Different value resistors can be
manufactured by changing the length and area of
crossection or the material itself which changes the
resistivity. Materials generally used for fabrication of
resistors are nichrome (80 % Ni and 20 % Cr),
constatntan (55% cu and 45 % Ni ) and Manmganin (85
% Cu and 10 % Mn and < 5 % Ni). Metals are not used
as they have a very high temperature coefficient of
resistance.
Three main methods of fabrication are (i) a slab or a rod
of suitable resistivity, (ii) Material using thinner
crossection and longer length. The length is doubled and
then wound in such a way that inductance effects are
cancelled out. (iii) Thin films of material on insulating
substrate. Each resistor has a current carrying capacity.
Current more than the prescribed wattage may damage
the resistor.
Colour Code for Resistors
Band colour & its Band colour & its tolerance
value
Black = 0 Gold = + - 5%
Brown = 1 Silver = + - 10 %
Red = 2 No colour means 20 %
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Grey = 8
White = 9
The first two bands near an end indicate first 2 digits,
digit corresponding to 3rd band is the power of 10 to be
multiplied and fourth band indicates tolerance as
mentioned in the table. Refer fig 1, where brown = 1,
black = 0, red = 2 and silver = 10 % tolerance. Hence its
value is
10 x 10 2 = 1 k .
Special purpose resistors
Light dependent resistors (LDR) and thermistors are
examples of special purpose resistors. Thermistor is a
resistor whose value depends on its temperature. It is
also called a heat sensor.
CAPACITORS
Capacitors are capable of storing charges. They are used
for coupling ac signals from one circuit to another and
for frequency selection etc. A capacitor consists of 2
metallic plates separated by a dielectric. The
capacitance is defined as : C = o r A / d, where A is the
area of plates, d is plates separation, o is permittivity
of free space and r is relative permittivity. An
important parameter for capacitors is its voltage
handling capacity beyond which the capacitor dielectric
breaks down.
The value of a capacitor depends upon the dielectric
constant (K = o r.) of the material. There are three
main classes of capacitors:
(i) Non electrolytic or normal capacitors and
(ii) electrolytic capacitors and
(iii) Variable capacitors.
Normal capacitors are mostly of parallel plate type and
can have mica, paper, ceramic or polymer as dielectric.
In the paper capacitors two rectangular metal foils are
interleaved between thin sheets of waxed paper and the
whole system is rolled to form a compact structure.
Each metal foil is connected to an electrode. In mica
capacitors alternate layers of mica and metal are
clamped tightly together. Refer fig 3.
In electrolytic capacitor mostly a then metal-oxide film
is deposited by means of electrolysis on axial electrode.
Thats how it derives its name. During electrolysis the
electrode acts as anode whose cathode is a concentric
can. Since the dielectric layer is very thin hence these
require special precaution for their use: i.e. they have to
connected in the right polarity failing which the
dielectric breaks down. Besides these fixed value
capacitors we also have variable capacitors whose value
depends upon the area of crossection. They have a fixed
set of plates and a movable set of plates which can be
moved through a shaft. This movement changes the
area of overlap of the two sets of plates which changes
its capacity. Refer fig 3.
Colour and Number code of capacitors.
Different marking schemes are used for electrolytic and
non-electrolytic capacitors. Temperature coefficient is of
minor importance in an electrolytic filter capacitor, but
it is very important in ceramic trimmers for attenuator
use. One never finds temperature coefficient on an
electrolytic label, but it is always present on ceramic
trimmers.
A number code is often used on small capacitors where
printing is difficult: the 1st number is the 1st digit, the
2nd number is the 2nd digit, the 3rd number is the power
of ten to be multiplied., to give the capacitance in pF.
Any letters just indicate tolerance and voltage rating. For
example: 102 means 10 X 10 2 pF = 1nF and 472J
means 4700pF = 4.7nF (J means 5% tolerance).
Capacitor Colour Code:
Sometimes capacitors just show bands like resistors
when printing is tough on them. The colours should be
read like the resistor code, the top three colour bands
giving the value in pF. The 4th band and 5th band are
for tolerance and voltage rating respectively. For
example: brown, black, orange means 10000pF =
10nF = 0.01F.
INDUCTORS
Inductor is a component made by a coil of wire
which is wound on a core. It is used to vary the
impedance of a circuit or for frequency tuning. The value
of an inductor depends upon the total number of turns
(N), area of crossection of the core (A) and length of the
core (l).The formula is L = o r N2 A / l. Its unit is in
Henry.
An inductor, also called a coil or reactor, is a passive
two-terminal electrical component which resists changes
in electric current passing through it. It consists of a
conductor such as a wire, usually wound into a coil.
Energy is stored in a magnetic field in the coil as long as
current flows. When the current flowing through an
inductor changes, the time-varying magnetic field
induces a voltage in the conductor, according to
Faradays law of electromagnetic induction. According
to Lenz's law the direction of induced electromotive
force (or "e.m.f.") is always such that it opposes the
change in current that created it. As a result, inductors
always oppose a change in current, in the same way that
a flywheel opposes a change in rotational velocity. Care
should be taken not to confuse this with the resistance
provided by a resistor.
An inductor is characterized by its inductance, the ratio
of the voltage to the rate of change of current, which has
units of henries (H). Inductors have values that typically
range from 1 H (106H) to 1 H. Many inductors have a
magnetic core made of iron or ferrite inside the coil,
which serves to increase the magnetic field and thus the
inductance. Along with capacitors and resistors,
inductors are one of the three passive linear circuit
elements that make up electric circuits. Inductors are
widely used in alternating current (AC) electronic
equipment, particularly in radio equipment. They are
used to block AC while allowing DC to pass; inductors
designed for this purpose are called chokes. They are
also used in electronic filters to separate signals of
different frequencies, and in combination with capacitors
to make tuned circuits, used to tune radio and TV
receivers.
Inductance (L) results from the magnetic field around a
current-carrying conductor; the electric current through
the conductor creates a magnetic flux. Mathematically
speaking, inductance is determined by how much
magnetic flux through the circuit is created by a given
current i
Inductors that have ferromagnetic cores are nonlinear;
the inductance changes with the current, in this more
general case inductance is defined as
Any wire or other conductor will generate a magnetic
field when current flows through it, so every conductor
has some inductance. The inductance of a circuit depends
on the geometry of the current path as well as the
magnetic permeability of nearby materials. An inductor
is a component consisting of a wire or other conductor
shaped to increase the magnetic flux through the circuit,
usually in the shape of a coil or helix. Winding the wire
into a coil increases the number of times the magnetic
flux lines link the circuit, increasing the field and thus
the inductance. The more turns, the higher the
inductance. The inductance also depends on the shape of
the coil, separation of the turns, and many other factors.
By adding a "magnetic core" made of a ferromagnetic
material like iron inside the coil, the magnetizing field
from the coil will induce magnetization in the material,
increasing the magnetic flux. The high permeability of a
ferromagnetic core can increase the inductance of a coil
by a factor of several thousand over what it would be
without it.
Types of inductor
Air core inductor
Radio frequency inductor
High Q tank coil in a shortwave transmitter
Ferromagnetic core inductor
Laminated core inductor
Toroidal core inductor
Choke
Variable inductor
TRANSISTORS
Transistors are semiconductor devices used for
applications like amplification of voltages, current and
are also used in oscillator circuits and switches. Its a
two junction and 3 terminal device made of three layers
of n and p type materials. The three regions are emitter,
base and collector. They are of 2 types (i) pnp and (ii)
npn. Their most important specifications are Ic, Vce, hfe
and Power rating. They come in different casings like
TO18, TO92C, and TO39 etc Given below is a table of
most commonly used transistors with their
specifications (approximate) and casings. Datasheets
from the companies can be referred to to know the
exact specifications.
Fig 9 gives some of the transistors with the symbols. for
npn and pnp. and fig 10 illustrates some of the casings.
with the configurations for emitter , base and collector
leads
MICROPHONES (MIC)
The Basics
Microphones are a type of transducer - a device which
converts energy from one form to another. Microphones
convert acoustical energy (sound waves) into electrical
energy (the audio signal).
Different types of microphone have different ways of
converting energy but they all share one thing in
common: The diaphragm. This is a thin piece of material
(such as paper, plastic or aluminium) which vibrates
when it is struck by sound waves. In a typical hand-held
mic like the one below, the diaphragm is located in the
head of the microphone.
Location of Microphone Diaphragm
When the diaphragm vibrates, it causes other
components in the microphone to vibrate. These
vibrations are converted into an electrical current which
becomes the audio signal.
Note: At the other end of the audio chain, the
loudspeaker is also a transducer - it converts the
electrical energy back into acoustical energy.
Types of Microphone
There are a number of different types of microphone in
common use. The differences can be divided into two
areas:
(1) The type of conversion technology they use
This refers to the technical method the mic uses to
convert sound into electricity. The most common
technologies are dynamic, condenser, ribbon and crystal.
Each has advantages and disadvantages, and each is
generally more suited to certain types of application. The
following pages will provide details.
(2) The type of application they are designed for
Some mics are designed for general use and can be used
effectively in many different situations. Others are very
specialised and are only really useful for their intended
purpose. Characteristics to look for include directional
properties, frequency response and impedance (more on
these later).
Mic Level & Line Level
The electrical current generated by a microphone is very
small. Referred to as mic level, this signal is typically
measured in millivolts. Before it can be used for anything
serious the signal needs to be amplified, usually to line
level (typically 0.5 -2V). Being a stronger and more
robust signal, line level is the standard signal strength
used by audio processing equipment and common
domestic equipment such as CD players, tape machines,
VCRs, etc.
This amplification is achieved in one or more of the
following ways:
Some microphones have tiny built-in amplifiers which
boost the signal to a high mic level or line level.
The mic can be fed through a small boosting amplifier,
often called a line amp.
Sound mixers have small amplifiers in each channel.
Attenuators can accommodate mics of varying levels
and adjust them all to an even line level.
The audio signal is fed to a power amplifier - a
specialised amp which boosts the signal enough to be
fed to loudspeakers.
CHAPTER-5
Advantages of FM bugger circuit
Resilient to signal strength noise: One of the advantages
of frequency modulation is that it does not suffer audio
amplitude variations as the signal level varies.
Does not require linear amplifier in the transmitter: As
only frequency changes are required to be carried, any
amplifiers in the transmitter do not need to be linear.
Enables greater efficiency than many other modes: FM
gives higher efficiency when compared to other modes.
DISADVANTAGES OF FM BUGGER CIRCUIT
The demodulator is a little more complicated, it is
slightly more expensive than the very simple diode
detectors used for AM. Also requiring a tuned circuit
adds cost.
Some other mode has higher data spectral efficiency:
Some phase modulation and QAM formats have a higher
spectral efficiency.
APPLICATION:
FM bugger circuit is used in spy agencies: In order to
listen the conversation of one person in the remote
location this circuit.
For security purpose: As it is designed for security
purpose, this cannot be used by all the persons.
CONCLUSION
FM bugger circuit cannot be used by all persons as it is
illegal, so the application based on this circuit is very
less. It is a very simple as it carries simple components.
To listen the conversation of one person where the
normal FM radio set is used in this project.
REFERENCES
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Communications Circuits - Design Project, pp. 1, April
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SA
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30
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