Chapter 1: Principles of Communications

Alessandro Volta

Invented the electric Battery

1799

What year did Alessandro Volta invent the electric battery

Joseph Henry

Transmitted the first practical electrical signal over one mile of wire to activate an electromagnet.

1830

What year did Joseph Henry transmitted the first practical electrical signal over one mile of wire to activate an electromagnet.

Samuel Finley Breese Morse

invented the telegraph.

1837

What year did Samuel Finley Breese Morse invented the telegraph.

Alexander Bain

invented the facsimile.

1843

What year did Alexander Bain invented the facsimile.

Transatlantic cable

was laid and failed.

1858

What year did Transatlantic cable was laid and failed.

Emile Baudot

designed a fixed-length binary code for telegraph.

1875

What year did Emile Baudot design a fixed-length binary code for telegraph.

Alexander Graham Bell

patented the telephone.

1876

The year Alexander Graham Bell patented the telephone.

Thomas Alva Edison

invented the phonograph.

1877

The year Thomas Alva Edison invented the phonograph.

James Clerk Maxwell

predicted mathematically radio propagation.

1864

The year James Clerk Maxwell predicted mathematically radio propagation.

Alexander Graham Bell

patented the photophone.

1880

The year Alexander Graham Bell patented the photophone.

1887

The year Heinrich Hertz verified experimentally Maxwell’s Theory.

Heinrich Hertz

verified experimentally Maxwell’s theory.

Friedrich Reinitzer

invented liquid crystal.

1888

The year Friedrich Reinitzer invented liquid crystal.

Guglielmo Marconi

Demonstrated wireless transmission.

1895

The year Guglielmo Marconi demonstrated wireless transmission.

Reginald Fessenden

invents AM (amplitude modulation).

1906

The year Reginald Fessenden invents AM (amplitude modulation).

Radio Station KDKA

broadcasts the first regular licensed AM radio transmission.

1920

The year Radio Station KDKA broadcasts the first regular licensed AM radio transmission.

Philo Farnsworth

produced the first all-electronic television transmission.

1927

The year Philo Farnsworth produced the first all-electronic television transmission.

Heinrich Lamm

was the first to transmit images through a single glass fiber.

1930

The year Heinrich Lamm was the first to transmit images through a single glass fiber.

Major Edwin Armstrong

invented FM (frequency modulation) radio.

1933

The year Major Edwin Armstrong invented FM (frequency modulation) radio.

1937

The year Alec Reeves invented binary coded pulse-code modulation.

Alec Reeves

invented binary coded pulse-code modulation.

1939

First use of two-way radio (walkie talkies)

1940

Invention and perfection of radar (World War II).

1946

The AT&T (American Telephone and Telegraph Company) inaugurated the first mobile telephone system for the public known as Mobile Telephone System.

1947

AT&T developed the concept of cellular telephony but the technology to realize the concept did not yet exist.

1954

Abraham van Heel, Harold Hopkins and Narinder Kapany announced imaging bundles, which propelled the fiber optics revolution and led to the development of flexible fiberscope.

1957

Russia launched the world’s first artificial satellite, Sputnik I.

1961

Citizens band radio (first use).

1962

NASA launches its first artificial satellite Telstar.

1970

HDTV (high-definition television) was introduced in Japan.

1972

Bob Kahn and Vint Cerf invented TCP (Transmission Control Protocol).

1973

Robert Metcalfe invents Ethernet to wire local computers together, and Martin Cooper of Motorola invented the first practical mobile phone.

1977

First commercial use of optical fiber cables.

1982

Internet development and first use.

1983

AT&T opened the first commercial cellular telephone system in the United States.

1991

im Berners-Lee invents the WWW (World Wide Web).

1993

First browser Mosaic.

1995

Global Positioning System deployed.

1996

First smartphones by BlackBerry, Nokia, and Palm.

1997

First WLANs (wireless local area networks).

1999

DTV (digital television) introduced. USA

2009

First fourth-generation LTE (long term evolution) cellular networks, and first 100 Gbps fiber optical networks.

BASIC COMMUNICATIONS SYSTEM

• It is a source of information, which must be delivered or transmitted to a particular destination over a channel.

• It is a collection of one or more electronic devices or circuits that converts the original source information to a form more suitable for transmission over a particular transmission medium.

• It performs encoding and modulation.

Modulator

it modulates the signal.

Amplifier

it provides power to the signal.

Oscillator

it provides the carrier signal.

Receiver

• It is the destination upon which information from the transmitter is delivered.

• It is a collection of electronic devices and circuits that accepts the transmitted signals from the transmission medium and then converts those signals back to their original form.

• It performs decoding and demodulation.

Demodulator (Detector)

It demodulates the signal.

Amplifiers

it provides power to the signal.

Output Devices

devices such as speaker, monitor, printer, etc.

Transmission Channel (Medium)

• It is the path or medium that the information travels from the transmitter to the receiver (i.e., it provides a means of transporting signals between a transmitter and a receiver).

• Attenuation occurs at this point.

attenuation

Sometimes referred as Power Loss

Guided Media

those with some form of conductor that provides a conduit in which electromagnetic energy are contained.

Samples of Guided Media

• Transmission lines (twisted pairs, twin lead, open-wire lines, coaxial cables, etc.)

• Optical fiber cables

• Waveguides

Unguided Media

signals are emitted then radiated through air or a vacuum (those signals propagating down the unguided transmission media is available to anyone who has a device capable of receiving them).

Examples of Unguided Media

• Free Space

• Earth’s Atmosphere

Amplifier

It is an electronic circuit which is capable of increasing the signal magnitude or amplitude without appreciably altering the signal waveform characteristics.

Class A

• Q point: active (linear) region

• Max efficiency: 25% or 50%

• Conduction Angle: 360

• Distortion: Low

Class B

• Q point: cut-off region

• Max efficiency: 78.5%

• Conduction Angle: 180

• Distortion: High

Class AB

• Q point: a little above cut-off region

• Max efficiency: between class A&B

• Conduction Angle: between 180-359

• Distortion: moderate

Class C

• Q point: below cut-off region

• Max efficiency: more than 90%

• Conduction Angle: less than 180

• Distortion: Very High

Oscillator

• It is a circuit that produces a periodic waveform on its output with only the DC supply voltage as an input.

• It is a non-rotating device for producing alternating current, the output frequency of which is determined by the characteristics of the device.

• It can be thought of as an amplifier that provides itself (feedback) with an input signal.

LC Oscillators

They used LC network (parallel resonant circuit or tank circuit) as frequency determining element. These are commonly used at high frequencies.

Hartley Oscillator

It uses a tapped coil as its feedback element.

Colpitts Oscillator

it uses a split capacitor as its feedback element.

Clapp Oscillator

it is similar with Colpitts with an additional capacitor in series with the inductor in the feedback circuit.

Armstrong Oscillator

t uses a tickler coil (transformer) as its feedback element.

RC Oscillators

they used RC networks to provide regenerative feedback and to determine the frequency of operation. These are widely used for low frequencies.

Wien Bridge Oscillator

it is a sinusoidal feedback oscillator that utilizes a lead-lag circuit.

Phase Shift Oscillator

it uses a series of RC sections.

Crystal oscillators

use specially-cut crystals to control the frequency, producing a highly stable and precise output. These are usually used to produce an output which is highly stable and at a very precise frequency.

Filter

• It is a frequency-selective circuit which are designed to pass some frequencies and reject others.

• Simple filters constructed by using resistors and capacitors or inductors and capacitors are called passive filters, because they use passive components that do not amplify.

• Some special types of filters are active filters that use RC networks with feedback in op-amp circuits, switched capacitor filters, crystal and ceramic filters, surface acoustic wave (SAW) filters, and digital filters implemented with digital signal processing (DSP) techniques.

Low-pass Filter

it passes frequencies below a critical frequency called the cutoff frequency and greatly attenuates those above the cutoff frequency.

High-pass Filter

it passes frequencies above the cutoff but rejects those below it.

Bandpass Filter

it passes frequencies over a narrow range between lower and upper cutoff frequencies.

Band-reject Filter

it rejects or stops frequencies over a narrow range but allows frequencies above and below to pass.

All-pass Filter

it passes all frequencies equally well over its design range but has a fixed or predictable phase shift characteristic.

Butterworth filter

effect has maximum flatness in response in the pass band and a uniform attenuation with frequency.

Chebyshev (Tchebychev) filters

have extremely good selectivity.

Cauer (Elliptical) filters

produce an even greater attenuation than do Chebyshev filters and greater attenuation out of the passband.

Bessel (Thomson) filters

provide the desired frequency response but have a constant time delay in the passband.

FREQUENCY

• It is simply the number of times a particular phenomenon occurs in a given period of time.

• It may be the number of voltage polarity alternations or electromagnetic field oscillations that takes place in a span of time; each alternation or oscillation is known as a cycle and the frequency is measured in cycles per second (cps), or better expressed as Hertz (Hz), named after Heinrich Hertz, who was a pioneer in the field of electromagnetics.

Period

It is the time required for one complete cycle of a repetitive waveform, and it is known as the reciprocal of frequency.