Principles of Electronic Communication

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Chapter 2: Principles of electronic communication systems

➢ Key words:

• Electrical and electronics
• Wires and cables
• Analogue electronics
• Digital electronics
• Information, message and data
• Analogue information
• Digital information

2 Introduction to electronic communication systems

2.1 Basic electronic components, symbols and circuits

Components of an electronic ( or electrical) circuit
Any electrical circuit consists if three (3) basic parts

Energy source - converts non-electric energy into energy. Examples are batteries and generators.

Output device - uses electric energy to do work. Examples are motor, lamp, or display.

Connection - allows electric current to flow. Examples are wire and cable.

Figure 2.1: Basic electric circuits.

The basic electronic communication circuit composed of electronic (or electrical) components are:

A voltage source
Capacitors, and

While the basic parameters of any electronic communication circuits are:

Voltage (in Volts)
Current (in Ampere), and
Power (in Watts)

Figure 2.2: The schematic diagram Resonant RLC circuit: Three components, R, C, and L connected to an AC voltage source: an ideal inductance, and ideal capacitance, and an ideal resistance in (a) Series-parallel and (b) Parallel.

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor.

Figure 2.3: R resister.

A potentiometer is a three-terminal resistor

Figure 2.4: Potentiometer.

Variable resistor:

Figure 2.5: Variable resistor.

A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates").

Figure 2.6: Capacitor.

An inductor is a passive electrical component with significant inductance.

Figure 2.7: Inductor.

A switch is a mechanical device used to connect and disconnect an electric circuit

Figure 2.8: Switches(s).

Two or more switches in parallel form a logical OR; the circuit carries current if at least one switch is 'on'. See OR gate.

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors


Figure 2.9: Transformer.

In electronics and electrical engineering a fuse (short for fusible link) is a type of over-current protection device.

Figure 2.10: Fuse.

Electric current
Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere. Electric current is measured using an ammeter. The electric charge may be either electrons or ions. The nature of the electric current is basically the same for either type.

Ohm's law
Ohm's law applies to electrical circuits; it states that the current through a conductor between two points is directly proportional to the potential difference (i.e. voltage drop or voltage) across the two points, and inversely proportional to the resistance between them. The mathematical equation that describes this relationship is:



I is the current, measured in amperes
V is the potential difference measured in volts
R is the resistance measured in ohms

Conventional current

Figure 2.11: (a) A voltage source, V, drives an electric current, I, through resistor, R, the three quantities obeying Ohm's law: I = V/R. (b) Diagram showing conventional current notation. Electric charge moves from the positive side of the power source to the...
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