ELECTRONIC COMMUNICATION SYSTEM

DEFINATION OF TERMS
COMMUNICATION: this is the exchange of information between the giver (source) and the receiver (destination) which is usually achieved with the help of a media (air, liquid or solid).

ELECTRONIC COMMUNICATION: this is the sending, processing and receiving of information using electronic equipment.

ELECTRONIC COMMUNICATION SYSTEM: this is a system that comprises the information source, a transmitter, a channel, a receiver and a destination which brings about complete information exchange.

History of Communication
Communication in general started by mere face to face signaling and voice communication between two parties (the giver and the receiver).

SIGNALING involves moving parts or whole of a thing (just like waving of hand means good bye) or using sound instrument like the talking drum to send out message.

VOICE COMMUNICATION involves two parties in a conversation or the town crier talking at a very loud voice giving information to the members of a community. In some cases, both signaling and voice communication are combined to ensure effective and better communication.

ELECTRONIC COMMUNICATION

Due to distance, population and other limiting factors, signaling and voice communication can no longer meet the demands to communicate effectively in our modern world. Electronic media are now a better tool to communicate effectively in our modern world. Electronic media are now a better tool to communicate effectively despite the distance or population which usually hampers information sharing. Electronic communication started with the wire telegraphy. The wire telegraphy just like the intercom devices of today is the basis in which the wireless media was invented though the wired telegraphy is wired. Because in wire telegraphy the transmitter and the receiver must be connected with wire, it becomes impossible to be used in a very far distance not to talk of across large water bodies like seas, oceans and rivers.

TYPES OF ELECTRONIC COMMUNICATION SYSTEM
 1. THE SIMPLEX COMMUNICATION [one way communication]: in this type of communication, the people at the sending side keep giving information to the people at the receiving end; but it is not possible for the people at the receiving end to respond via the same means to the sender. Examples of simplex communication are found in Radio broadcasting and Television broadcasting where the listeners are made just to listen without feed back.
The communication equipment at the receiving side has only a receiving circuitry and no transmitters. So he/she can only receive and not respond.

 2. HALF DUPLEX COMMUNICATION: this is a two way communication system where the sender and the destination can talk to each other but not simultaneously. The communication equipment at both the sending and receiving ends have inbuilt receiver and transmitter so to allow both parties to answer back but not at the same time. Example, the police walkie-talkie. When a police sergeant and another police recruit want to communicate, assuming the sergeant and the recruit have information to exchange and both are separated by are large distance, the sergeant presses a button which alerts the recruit to pick up his walkie-talkie. At this point only one of them will be talking and the other listens after which both officers switch over so that the one talking will be receiving and the other does the talking.

 3.  FULL DUPLEX COMMUNICATION: this is the communication equipment that makes sending and receiving of information to be done simultaneously. This is the technology of GSM and telephone. The switch over protocol employed in the half duplex is useless here. Parties involve in the conversation can keep talking at will till the end of the conversation.

BLOCK DIAGRAM OF AN ELECTRONIC COMMUNICATION SYSTEM

INFORMATION SOURCE: this can simply be put as a person or thing that has the information to be shared. The function of a communication system is to convey message. This message is originated from an information source.
TRANSMITTER: this is an electronic device that converts sounds digital/analogue information into electrical signal which is thereafter modulated (converted to electromagnetic radio frequency) before radiating into the air through an antenna.
CHANNELS: these are medium (air, liquid, vacuum or solid) which serve as the carrier of the modulated signal. Without channel it becomes impossible for any form of communication to be achieved.
RECEIVER: this is an electronic device that intercepts the radiated signal, change it (demodulate) back to sound, digital/analogue information. At this point, the original information that was sent will be recovered. Examples, TV and Radio sets at homes.
DESTINATION: this is a person or a thing the information was targeted before transmitting the message. Examples people watching TV or listening to radio, staying on earth and controlling satellites in space.



NOISES IN COMMUNICATION

These are unwanted energy which combines with the main information in a way that makes the information at the source to vary when it gets to the destination. Noise is responsible for the hissing sounds in radio receivers. Noise makes TV not to be clear. Whenever there is bad reception in radio or TV it is as a result of noise. Electronic components used in the design of the receiver and transmitters a times introduce noise to distort the original information. In other case, the medium or channel used for the transfer of the information can cause noise.

TYPES OF NOISE
 1. EXTERNAL NOISES: these are noises that originate from the medium used in information transfer. All kinds of noise created outside the transmitter and receiver come under the external noise. And these noises include atmospheric noise, extra terrestrial noise and industrial noise.

 2. INTERNAL NOISES: these are noise generated by electronic components used in the design of tran smitters and receivers. Resistors, capacitors and diodes and transistors are generally being affected by temperature. The kinetic theory of matter states that the molecules of a substance (solid, liquid and gas) are in constant random motion which also is dependent on temperature.


ELECTROMAGNETIC SPECTRUM

Every current carrying conductor has magnetic field and that is the origin of electromagnet. This jumping off electrons are responsible for magnetic field creation of current carrying electrons.

DEFINATION OF TERMS
ELECTRIC FIELD: this is a force field created as a result of movement (rush) of electrons. It should be noted that during this rush, some electrons do escape into the air which is responsible for the creation of magnetic field around the conductor.

MAGNET: this is a device possessing excessive electrons and also having enough internal energy capable of forcing these electrons to escape into the air. This jumping off electrons is responsible for its ability to attract metals which are electrons seeking substances.


NATURAL MAGNET: this is a stone found naturally in this world with enough internal energy that causes the liberation of its electrons into the air. This stones are found naturally in some Asian countries. At this point, these liberated electrons have little or no effect to the atmosphere since it has zero frequency.
ARTIFICIAL MAGNET: this is a metal, a coil or both that has been made magnetic by the activities of man on it. At this point, the liberated electrons have no frequency.

ELECTROMAGNET: this is another kind of artificial (made man) in which electrons are forced to leave the conductors by the passage of electric current through it. For the fact that electrons must be liberated once current is set flowing through a conductor, every current conductor has magnetic field around it. And also in every magnetic field there must be electron flow (electric current/field) at this point the liberated electrons have no frequency.

ELECTROMAGNETIC WAVE
This is a disturbance in the air caused by the liberated electrons into the air in most cases via an antenna. At this point frequency is of utmost importance. Just like every other waves, this electromagnetic wave experiences these properties
 1. Reflection
 2. Refraction
 3. Interference
 4. Diffraction

Since electromagnetic waves depend largely on frequency a chart has been compiled to show these different frequencies so as to help in the study of the properties of electromagnetic wave and the chart is called electromagnetic spectrum.

ELECTROMAGNETIC SPECTRUM CHART


Electromagnetic Spectrum: This is a chart that clearly shows the various frequencies of the electromagnetic waves. It should be noted that electromagnetic waves affect us differently depending on the way these liberated electrons affect the air around us. The speed of vibration of liberated electrons gave birth to electromagnetic induction, radio wave, infra-red rays, visible light/spectrum, x-rays, gamma Rays and the cosmic rays. In wireless communication these frequencies of electrons have played important roles.

APPLICATIONS OF ELECTROMAGNETIC WAVES
 1. GENERATORS, MOTORS, SERVO-MOTORS, TRANSFORMERS, RELAY employ the concepts of electron liberation at a very low frequency (10hertz – 1kilohertz) for its operation. This is achieved by applying a changing or not changing voltage (ac 50Hz ) into a coil of wire to create a magnetic field which can be used for rotating a device (motors), a generatoror in electromagnetic relays.
 2. Radio waves (104Hz to 1010 Hz): at this level of frequency, liberated electrons can be intelligently used for transmission of information (wireless communication).
 3. Infra-red (1011Hz to 1014 Hz): electrons vibrating at this frequency behave like invisible light. This is used in the design of wireless remote control systems and other kinds of short distance communication.
 4. Visible Spectrum/Light (above 1014Hz and below 1015): at this very narrow frequency, electrons become a shinning light. It is at this frequency that we humans and animals are made to see.
 5. Ultra-Violet ray (1015Hz to 1016Hz): at this frequency electrons becomes a bit dangerous to us. It can also be used in photography. It is also responsible for sun burn.
 6. X-Rays (1017Hz and bellow 1019): electrons vibrating at this frequency can pass through opaque objects. X-Rays are used in taking photograph of broken parts of things that are hidden internally away from ordinary eyes.
 7. Gamma Rays (1019Hz and below 1021Hz): vibrating electrons at this frequency are used for the destruction of cancerous cell in the medical field.
 8. Cosmic Rays (above 1021Hz): these are rays emitted by the stars, sun and other heavier celestial bodies for now these electrons at these frequency is simply a threat to human life.




POWER SUPPLY

This is a section in every electrical appliance responsible for energizing the entire system. Beginning from a single battery to a very complex power converting system make up the power supply.

SOURCE OF ENERGY FOR POWER SUPPLIES
Power supply units source their energy from a direct current source like battery or an alternating current sources like electrical energy generating set.
DIRECT CURRENT (DC)
This is current whose energy supply has no observable instantaneous flow rate variation. Remember, current is a directional flow of electrons. In Direct Current power supply systems, the quantity of electron flowing does not reverse its direction.
Example, electric power from battery.
BATTERY
A battery is a device that converts stored chemical energy into useful electrical energy used as a power supply to most of electrical appliances. A single unit within a battery compartment that can independently deliver voltage is referred to as CELL. Battery is a term used when two or more cells are interconnected to give a higher voltage or current. In summary, anything called battery contains more than one cell.
TYPES OF BATTERY All the battery in this world can be grouped into rechargeable (secondary cell) and non rechargeable (primary cell).
1.    PRIMARY CELL (non rechargeable): these are battery that cannot be recharged.
  Alkaline battery
  Aluminium-air battery
  Atomic battery
  aniel cell
  Galvanic cell leclanche cell
2.    SECONDARY CELL (RECHARGEABLE BATTERY): these battery can be recharged
  Lead accumulator
  Lithium battery
 1. Flow battery
  Fuel cell
   Nickel-Cadmium battery
  ickel-Zinc battery


GRAPHICAL SYMBOLS OF BATTERY

TESTING A BATTERY
For the purpose of this lesson, using multimeter will be enough to give us the basic test we wish to conduct. It is testing for the battery voltage (charge) level, and also polarity.

APPLICATION OF BATTERY
Cell phones, robots, toy cars, torchlight, inverters, laptops, electric motors, radio, television, space craft etc.

Advantages of DC Systems
Most electrical appliances prefer DC for its internal operation since it has no frequency that can affect the way they operate. DC systems are also very portable.

DISADVANTAGES OF DC SYSTEMS
Long distance transmission of DC power is very difficult; this is because long distance power transmission systems require the voltage to be stepped up so that energy loss will be negligible. Stepping up/down of DC power requires complex circuit whose complexity increases with electrical power increase.


ALTERNATING CURRENT (AC)
This is a current/voltage whose instantaneous quantity varies with time this is as a result of reversal in direction of electron flow. This is usually caused by a power source whose supply voltage is changing with time. E.g. electrical power from alternators.
Systems generating AC usually come with alternators
1.     Bicycle dynamo
2.     Hydroelectric power generators
3.     Gasoline Generators
4.     Wind turbine

ADVANTAGES OF AC POWER SUPPLY
Can very easily be transmitted to long distance places for distribution, this is because it is not difficult to step up/down its voltage. This is also why most electrical energy consumed in Nigeria is AC system.

Disadvantages
This system is very heavy, expensive to buy and use.


AC TO DC CONVERSION
Alternating Current (AC) and Direct Current (DC) are used in driving electrical appliances. Some electrical appliances require AC to work while others require DC. Whether AC or DC, both serve simply as power to electrical devices.
Most devices we use at home require DC, but public electrical powers supplied to us (GENERATORS, NEPA, PHCN OR DISCO) are AC. This does not mean we won’t be able to use this AC supply in driving our DC devices. Builders of television sets, radio sets, computers e.t.c., knew this and designed these systems to have AC to DC conversion circuit that made it possible for us to plug these systems directly to 220 volt source and it works perfectly. As students of electronics, we will want to also plug our electrical project we built directly to 220 volt AC without damaging our appliances. Before we can do this, we have to convert this AC to DC.


AC TO DC CONVERTER CIRCUIT DIAGRAM DESIGN AND ANALYSIS
COMPONENTS USED, CIRCUIT SYMBOL AND FUNCTION
AC CORD:

this is simply a wire that connect house sockets to our power supply


TRANSFORMER:

this is an electromagnetic device that has two electrically isolated coil of wire around a suitable core (iron core, ferrite core etc) that can step up/down AC current. In the case of what we are doing we used a step down transformer to simply step down high electrical voltage at home to 24volt.

BRIDGE RECTIFIER:
this is bridge connected four rectifying diodes circuit responsible for actual conversion of AC to DC, this is because it allows electrons to flow through it in one direction. It can be built by arranging four diodes as shown below.

CAPACITOR:
this is an electronic component that store electrons faster than it discharges. This singular characteristic is responsible for its being able to serve as ripple DC smoothening device (filtering component).

REGULATOR:
this is a circuit that takes unstable power input and bring out stable output power. Most AC power sources very unstable even after converting it to DC at capacitor stage keeps fluctuating. Most projects require very stable power supply to function properly. LM317 Regulator is very good in ensuring our output power remains stabilized.

POTENTIOMETER (variable resistor):
this component limits the flow of electron in a variable way. In order for us to be able to change the voltage quantity of our regulated output our design has this component integrated.

RECTIFYING DIODE:
this semiconductor element allows current to pass through it in one direction; this is while it can cause alternating current to become direct current when placed in path of AC flow. It can also be used to protect some components from damaging current, like in our power supply it was also used to protect the regulator.

FIXED RESISTOR:
this component is used to limit the flow of electrons. Due to its electron limiting ability, it can cause required voltage to be dropped.

COMPLETE CIRCUIT DIAGRAM DESIGN


ANALYSIS OF THE COMPLETE CIRCUIT DESIGN
The AC input which is usually 120volts to 240volts is picked up by the AC cord connected to the electrical socket to the step-down transformer. The transformer steps the voltage from high alternating voltage to very low alternating voltage (12v to 24v). Remember transformer simple steps down and feed into the bridge rectifying diode. The bridge rectifier is the main component that actually converts AC to DC before feeding into the capacitors. The capacitors as stated earlier smoothen the DC output of the bridge diode before feeding into the regulator. The regulator with its variable resistor, fixed resistors and 10uf capacitor is responsible for the entire system to be able to produce variable regulated DC. The 470uf capacitor is used to ensure that during switch off and switch on of the entire system the load is not affected. The led tells us that our circuit is either on or off.




TRANSDUCER

This can be defined as a process, a substance or a mechanism capable of converting energy from one form to another. It is known that energy exists in different forms like
1. Mechanical energy
2. Chemical energy
3. Light energy
4. Heat energy
5. Sound energy
6. Magnetic energy
7. Electrical energy
Therefore, anything capable of converting energy from one form to another is regarded as a transducer.

TYPES OF TRANSDUCER
INPUT TRANSDUCER (SENSOR): this is a device capable of sensing physical quantity and converting it to another form of energy that the system of its use can work with.

OUTPUT TRANSDUCER (ACTUATOR): this is a device capable converting its input energy into another form to be used by an independent system. For instance, electrical pulses sent into the loud speaker are converter into sound energy for human consumption. Though, humans are not directly part of the system that produced the sound but react somehow to the produced sound.

VARIOUS KINDS OF TRANSDUCERS
1. COMBUSTIBLE/RESPIRATION/DIGESTION: are all processes that convert chemical energy into heat, mechanical or light energy as the case may be.
2. MOTORS: these are mechanisms capable of converting electrical energy to mechanical energy. E.g. fan and other rotating mechanisms based on coils.
3. BULBS: these a mechanisms capable of converting electrical energy to light energy
4. PHOTO-VOLTAIC CELL: these mechanisms are capable of converting light energy to electrical energy.
5. HEATER: these mechanisms or process convert electrical or chemical energy to heat energy. E.g. boiling ring, pressing iron, electric stove, kerosene stove etc.
6. LOUD SPEAKERS: these mechanisms convert electrical energy to sound.
7. MICROPHONES: these mechanisms convert sound energy to electrical energy.
8. INDUCTORS/COILS: these mechanisms convert electrical energy to magnetic energy.
9. MAGNETIC LOCKS AND KEYS: these mechanisms convert magnetic energy to mechanical energy.
10. ELECTROMAGNETIC RELAYS: these mechanisms convert electrical energy to magnetic and mechanical energy simultaneously.
11. VIDEO CAMERA: these mechanisms convert light energy to electrical energy.
12. VIDEO DISPLAY UNIT: converts electrical energy to light energy.
13. THE FIVE HUMAN SENSE ORGANS: these are specially designed transducers capable of converting energy from one form to another.


MODULATION

This is the process of superimposing (combining) a low frequency (long wave) voice information components to a high frequency (short wave) carrier signal before transmission of the information.

WHY MUST WIRELESS INFORMATION BE MODULATED
It should be noted that in theory, it is possible to transmit human voice (audio frequency) using the electromagnetic spectrum. But in practice, it cannot be achieved because
1. Antenna Requirement: the shortest antenna length that can effectively transmit and receive atthe maximum human audio frequency i.e. 20KHZ should be 375 Km in length. The lower the frequency the taller the antenna must be. This is one of the reason propagating information at such low frequency cannot be done.
2. Excess noise: if transmission is to be made at human audio frequency range, the atmosphere will be filled with audible sounds from every radio transmission in the air. We won’t be needing radio at our homes since the sound will naturally be audible in our ears. But one would wonder how noisy and inhabitable our world will be if transmission is to be done at audio frequency.
3. Excessive interferences: if every radio station is to be given a bandwidth within 20Hz to 20 kHz; the interferences of this transmission stations at such narrow frequency will make transmission from more than one station impossible.
Therefore, we modulate in other to have a very short antenna, noise free atmosphere and a space where bandwidth is large enough to accommodate many radio stations simultaneously.

SINUSOIDAL WAVE PROPERTIES
DEFINATION OF TERMS
1. AMPLITUDE (A): this is the maximum displacement of the particles of wave.
2. WAVE LENGTH (): this is the distance covered by a complete cycle of a given wave.
3. PERIOD (T): this is the time taken by a wave to make a complete cycle.
4. FREQUENCY (f): this is the number of cycles a wave makes in one second. It is measured in Hertz (Cycles/second)

MODULATING SIGNAL
This is the natural frequency of human voices which is usually the intelligent to be transmitter.
THE INTELLIGENT SIGNAL (low frequency)
These are low frequencies of the human voice which is usually called the modulating signal. It is remarkably known for its unpredictable frequency and amplitude variation. The sound produced by the human voice contains so many frequencies (harmonics) combined together. But to simplify this phenomenon, a single frequency is usually used when sketching the modulating signal.
UNIT INTELLIGENT SIGNAL UNDER STUDY

CARRIER SIGNAL (WAVE)
This is a high frequency wave (radio wave) which is used to carry the human voice over the air. This carrier wave helps us to overcome the problems encountered while trying to transmit human voice directly.
HIGH FREQUENCY CARRIER SIGNAL
The carrier waves alone contain no information at all, if not modulated (combined with modulating signal), it is so because its amplitude, frequency or phase angle does not change with time. It is only when it is superimposed with modulating signal that it carries a message.

TYPES OF MODULATION
Every wave has phase angle (), Amplitude (A), and frequency (f). Depending on the property of the wave that is varied that tells the type of modulation in use.
1. Frequency Modulation [FM]: this kind of modulation is a case where the human voice causes the carrier frequency to vary with time in response to voice variation but the amplitude and phase angle of the carrier signal are constant.
Frequency Modulator Radio Operations


2. Amplitude Modulation [AM]: in this kind of modulation, the modulating signal causes the amplitude of the carrier signal to vary with time in response to the varying modulating signal but the frequency and phase angle of the carrier are constant.
Amplitude Modulator Radio Operations

3. Phase Modulation [PM]: in this type of modulation, the phase angle is made to vary with time in response to the variation of the modulating signal; at this point the frequency and Amplitude are held constant.
Frequency Modulator Radio Operations


THE AM ENVELOPE
This is a graphical representation of AM waves used to simplified explain better the true nature of AM waves.
AM ENVELOPE GRAPH
In reality it is difficult to represent graphically electromagnetic frequency (carrier signal), since it is in Megahertz. So in other to simply the true structure of an AM signal, an envelope called the AM envelope is employed.


DEMODULATION
This is the process of extracting the original transmitted voice still combined with the carrier waves at the time of reception by the receiver’s antenna. Since modulation took place in the transmitter, the reverse process of this is demodulation which takes place in the receiver to recover the original modulating signal.

DEMODULATED SIGNAL
TYPES OF DEMODULATOR
 1. AM Demodulator
 2. Envelope detector
 3. Product detector
 4. FM Demodulator
 5. Quadrature detector
 6. Radio detector
 7. Digital Signal processing
 8. PM Demodulator



SOLDERING AND DESOLDERING IN ELECTRONIC CIRCUIT

Definition: soldering is process in which two or more items (usually metal) are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal.
PRECAUTIONS TO BE OBSERVED WHILE SOLDERING
 1. Never touch the element of the soldering iron.
 2. You may hold wires to be heated with tweezers or clamps.
 3. Keep the cleaning sponge wet during use.
 4. Always return the soldering iron to its stand when not in use.
 5. Never put it down on the workbench.
 6. Turn unit off and unplug when not in use.
 7. Wear eye protection. Solder can "spit".
 8. Use rosin and lead -free solders wherever possible.
 9. Keep cleaning solvents in dispensing bottles.
 10. Always wash your hands with soap and water after soldering.
 11. Avoid smokes and fumes from soldering by staying in well ventilated work area.
 12. Wear hand gloves so that you don't touch soldering lead.
 13. Do not use soldering irons that have obvious damage to body, cable or plug.
 14. Keep the soldering station free of electrical cables to prevent damage from the heated tip.
 15. Use a grounded outlet and grounding prong if a short circuit is a possibility.
 16. Work on a fire-proof or fire resistant surface.
 17. Wear fire resistant clothing (e.g. 100% cotton) that covers your arms and legs
 18. to prevent accidental burns.
 19. Know where your nearest fire extinguisher is and how to use it.


SOLDER TYPES

Solder is basically metal wire with a "low" melting point. For electronics, it is traditionally a mix of tin and lead. Lead has a lower melting point than tin, so more lead means a lower melting point. Most common lead-based solder you'll find at the gadget store will be 60Sn/40Pb (for 60% tin, 40% lead).

FLUX This is a chemical that cleans and de-oxidize the surfaces of metal we are trying to solder. Flux is a substance which is nearly inert at room temperature, but which becomes strongly reducing at elevated temperatures, preventing the formation of metal oxides. Additionally, flux allows solder to flow easily on the working piece rather than forming beads as it would otherwise. The role of a flux in joining processes is typically dual: dissolving of the oxides on the metal surface, which facilitates wetting by molten metal; and acting as an oxygen barrier by coating the hot surface, preventing its oxidation. In some applications molten flux also serves as a heat transfer medium, facilitating heating of the joint by the soldering tool or molten solder.
Electronics flux can be rosin, water-based, or no-clean. All are about the same quality as far as de-oxidizing the copper so a good solder bond can be made.
 1. ROSINE FLUX: Rosin based fluxes are made from rosin which is extracted from pine sap. Rosin flux leaves an ugly, sticky residue. Cleaning it off takes either a LOT of water, or a (nasty) chemical solvent. You shouldn't leave it on, as it is slightly corrosive, and can also be somewhat conductive. This is falling out of usage due to the environmental impact of cleaning.
 2. WATER SOLUBLE FLUX: The so called water soluble fluxes are divided into two categories, organic and inorganic based on composition. Organic fluxes are more active than RA rosin, and inorganic are the most active of all. Water-based (aka Resin) flux is less ugly, not sticky.
 3. "No-clean" flux is resin flux that burns or boils off, leaving almost no residue.