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GENERAL INTRODUCTION
1.0 INTRODUCTION
Frequency Modulation (FM) transmitter bugs are audio surveillance devices that can be placed in an environment, on a person, and left behind to work as covert transmitters or bugging devices. Audio bugs do not always look like bugging transmitters built onto a miniature vero board with an antenna.
Bugging simply means to secretly listen to or record a conversation using a hidden electronic device. This devices are of different variety depending on the place and where the bug can be placed. While surveillance on the other hand is the monitoring of the behaviour, activities, or change of information, usually of people for the purpose of influencing, managing, directing or protecting them. Surveillance is used by governments for intelligence gathering, the prevention of crime, the protection of a process, person, group of object, or for the investigation of crime. It is also used by criminal organizations to plan and commit crime such as robbery and kidnapping. By businesses to gather intelligence, and by private investigation. But surveillance is often a violation of privacy, and is opposed by various civil liberties group and activities.
These audio bugs are offered in disguised versions in order to limit their accidental discovery should one be noticed. Because of the need for secrecy, covert transmitters and other bugging devices upon first glance may resemble regular items like, TV remote control, or cigarette lighter. That way, no one would suspect that the true nature of those objects were actually bugging devices use for monitoring conversations. [1]
A covert listening device, more commonly known as a bug or a wire, is usually a combination of a miniature radio transmitter with a microphone. The use of bugs, called bugging, is a common technique in surveillance, espionage and in the process of investigations by security agencies.
A bug does not have to be a device specifically designed for the purpose of eavesdropping. For instance, with the right equipment, it is possible to remotely activate the microphone of cellular phones, even when a call is not being made, to listen to conversations in the vicinity of the phone.
From the block diagram we can easily understand that the audio is picked up by the input(MIC) and the message signal (weak signal) is amplified. The audio (or data) signal is modulated onto the radio frequency carrier in the modulator stage. The Frequency generation stage (often known as the oscillator) defines the frequency on which the transmitter will operate,the modulated signal is then transmitted via the antenna. User should adjust the receiver frequency in the radio for receiving the signal from the transmitter.
1.1 AIM AND OBJECTIVES
To design and implement a low power FM transmitter surveillance bug circuit. And the objectives are
(i) To build an FM transmitter that can operate between 88 MHz and 108 MHz
(ii) To transmit within the range of around 100 meters.
(iii) To make the transmitter small enough to avoid detection.
1.2PROJECT MOTIVATION
Due to the growing menace of terrorist groups in Nigeria and the challenges of security agencies to cub their activities. The construction of this FM bug circuit is an attempt to equip the security agencies with a tool to eavesdrop on the operations of the terrorist group which will serve to gain information that will enhance their activities. Another motivation is that the project will be done with low cost components that are found in workshops, laboratories and electronic stores.
1.3PROBLEM DEFINITION
The problem calls for a device that will receive an input signal and broadcast it on the FM band. The device is to receive its signal input from the microphone and its power input from the 9V DC battery. It should be easily tunable to transmit on any desired frequency in the FM band (88-108 MHz). The minimum transmission distance is to be at least 100m. It should recognize when there is an input signal and pick it up automatically and automatically transmit the signal.
1.4METHODOLOGY
The method in which the design and construction will be carried out is divided into five sections namely;
(i) The MIC unit.
(ii) The transmitter unit.
(iii) Transistor (Amplifier) unit.
(iv) The tank circuit unit.
(v) The receiver unit.
1.5 APPLICATION
The FM transmitter surveillance bug circuit finds applications in the following areas;
(i) It can be used as a bugging device.
(ii) It can be used as an FM transmitter.
(iii) With proper modification it finds use in mobile phone jamming of signals.
1.6PROJECT OUTLINE
This project report consists of five chapters, chapter one contain General introduction of the project, chapter two: Literature Review and theoretical background of the project, chapter three: system design and calculation, chapter four: construction, testing and packaging, and finally, chapter five: conclusion and recommendation.
SURVEILLANCE
Surveillance is defined as conducting close observations of an individual or a group. One of the most common and oldest techniques to surveillance is to actually follow and watch the individual. Such practices are fast becoming outdated. A new form of surveillance known as electronic surveillance is now the common method employed,Electronic surveillance is a way of monitoring a home, business, or individual using a variety of devices such as CCTV (closed circuit television), television, wiretapping, cameras, digital video equipment, and other electronic, digital, and audio-visual means). Today, electronic surveillance can also refer to surveillance done by or on a computer or mobile phone. For example, computer surveillance can include e-mail tracking, internet surveillance, remote PC surveillance, and other forms of monitoring a computer for suspicious activity. Mobile phone surveillance is quickly becoming a more important tool as well. Agencies have begun to rely on technology to complete surveillance. They now use bugging devices or CCTVcameras for surveillance purposes. These devices can be used for room monitoring, when a baby is fast asleep or for nature research and so on. These help in security purposes also by picking up noise made by intruders alerting the monitoring party. Surveillance is also used by big companies against their competition by spying on them and knowing their plans going forward. [2]
2.1 TRANSDUCER
A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.
An acoustic transducer is an electrical device that coverts sound wave vibrations into mechanical or electrical energy. They have various practical applications, including sound recording and sound playback. A specialized model, called an ultrasonic acoustic transducer, can be used to measure distance to, as well as the mass of, an object.
Common types of acoustic transducers used in sound recording include microphones, earphones, and guitar pickups. These create electrical energy when moving parts inside the transducer, such as electrical plates or ribbons, are exposed to sound vibrations. The electrical energy produced inside the transducer is sent first to an amplifier.
The amplifier then sends this energy to its final destination, usually a loudspeaker or recording device. The loudspeaker reproduces the sound at a level that the human ear can hear. A recording device will retain the electrical signal information. The recorder will send the stored signal to a loudspeaker during playback.
An ultrasonic acoustic transducer can be used to measure distance or the mass of an object. The most common type is the piezoelectric acoustic transducer. These include a piezoelectric ceramic element that creates and distributes ultrasonic sound waves
A microphone, colloquially mic is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Electromagnetic transducers facilitate the conversion of acoustic signals into electrical signals. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, two-way radios, megaphones, radio and television broadcasting, and in computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock sensors.
Most microphones today use electromagnetic induction (dynamic microphones), capacitance change (condenser microphones) or piezoelectricity (piezoelectric microphones) to produce an electrical signal from air pressure variations. Microphones typically need to be connected to a preamplifier before the signal can be amplified with an audio power amplifier and a speaker or recorded. The microphone that will be used in this write up is the electret microphone.
An electret microphone is an omnidirectional microphone, which means it can capture sound from all directions. What sets it apart from types of microphones is how it transmits sounds to output devices.It uses two conducting plates; one is fixed while the other is a vibrating diaphragm. This kind of design is found in all capacitor microphones, which are types of microphones that deliver great sound quality but requires a constant source of electrical charge to produce electrical signals that communicates the sounds made by the diaphragm into sound that comes out of outputs devices likes speakers. What makes it different from generic capacitor microphones is that it does not need a constant source of electrical charge. Its diaphragm is actually made of insulating material that contains a permanent electrical charge. This makes it very efficient by producing quality sounds without requiring a constant source of electrical charge.
With the diaphragm and the back plate ready to receive sound waves, they work by letting the incoming sound waves from a source of sound from any direction to change the capacitance between the two conducting plates. The diaphragm is the conducting plate that receives the sound waves and it causes the change in capacitance. This change in capacitance produces variance in voltage on the back plate and this, in turn, sends electrical signals to output devices like speakers and sound systems. It may seem magical and mind-blowing, but this technology has been around for decades. Its simplicity lets it stand the test of time and even with some modifications through the years, the basic principle of using two conducting plates to deliver electrical signals that represent sound waves. [3]
2.2 AMPLIFIER
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal.
It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier modulates the output of the power supply to make the output signal stronger than the input signal. An amplifier is effectively the opposite of an attenuator: while an amplifier provides gain, an attenuator provides loss.
An amplifier can either be a separate piece of equipment or an electrical circuit within another device. The ability to amplify is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment. The types of amplifiers can be categorized in different ways. One is by the frequency of the electronic signal being amplified; audio amplifiers amplify signals in the audio (sound) range of less than 20 kHz, RF amplifiers amplify frequencies in the radio frequency range between 20 kHz and 300 GHz. Another is which quantity, voltage or current is being amplified; amplifiers can be divided into voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers. A further distinction is whether the output is a linear or nonlinear representation of the input. Amplifiers can also be categorized by their physical placement in the signal chain.
Amplifiers may also be classified according to the bandwidth which may be low or high. Another way of classifying amplifier is biasing signals. These can be differentiated into different class such as A, AB, B and C or according to their mode of operation i.e on some predetermining set of values which are based on some factors like: as a base on input signal, as base output signal, as a base on biasing condition, as a base on frequency response and base on transistor configurations etc.
One very important method to classify an amplifier is based on its transistor configuration .The following category of this class is as follows
Characteristics of CE Amplifier
The CE amplifier has the following characteristics
i. It has moderate input impedance (1kΩ to 2kΩ).
ii. It has large output impedance of 50kΩ.
iii. It has high current gain (100 to 200).
iv. It has high power gain (1000 to 10000).
v. It has high voltage gain (100 to 1000).
vi. It has low to medium limiting frequency.
vii. The phase difference between the input and the output signal is 180 degree.
The CE amplifier is most widely used in actual practice because of large voltage gain, power gain. Moreover its input and output resistance are suitable for most of the application, hence it will be used in this project.
c. Common Collector (CC) Amplifier
In the common collector amplifier the input signal is injected into the base collector circuit and the output signal is taken from collector emitter circuit. The emitter base junction is forward biased by VEE and the collector base junction is reversed biased by Vcc. The common collector amplifier are also called the emitter follower.A typical circuit of CC amplifier is shown in figure below.