Fundamentals of Communication Systems

• Communication involves exchanging information
• Language and distance create main communication barriers
• Contemporary emphasis is on collecting, packaging, and exchanging information

Methods of Communication

• Face to face
• Signals (smoke, light, flag)
• Written word (letters by courier)
• Electrical innovations have changed communications, including:
  • Telegraph (1844, single-tone signal w/ Morse code)
  • Telephone (1876, voice over wire)
  • Radio (1887)
  • Television (1923)
  • Internet/computers (1970s-1980s)

Communication System Components

• Transmitter converts electrical signal to transmittable signal
  • It consists of oscillators, amplifiers, tuned circuits, filters, modulators, frequency mixers, and frequency synthesizers
• Communication channel is the medium for electronic signal transit
  • Includes electrical conductors, optical media, free space, and system-specific media (water for sonar)
• Receiver accepts transmitted message, converts it into understandable form
  • It contains amplifiers, oscillators, mixers, tuned circuits, filters, and a demodulator
• Noise is random electronic energy that interferes with the transmitted message via the communication medium

Transceivers

• Transceivers incorporate send and receive circuits
• Examples are telephones, fax machines, handheld CB radios, cell phones, and computer modems

Signal Attenuation

• Signal degradation exists in all wireless transmission media
• It is proportional to the square of the distance between transmitter and receiver

Types of Electronic Communication

• Simplex: One-way communication
  • includes radio and TV broadcasting
  • Transmitting to remotely controlled vehicles like drones
• Half Duplex: Two-way, one party transmits at a time
  • Includes police, military, citizen band (CB), family, and amateur radio
• Full Duplex: Two-way communication where both parties can talk/listen simultaneously
  • Telephones are an example

Types of Signals

• Analog Signals: Smoothly/continuously varying voltage/current (sine wave, voice, video)
  • First digitized with an analog-to-digital (A/D) converter for processing
• Digital Signals: Change in steps/discrete increments
  • Use binary/two-state codes
  • Includes telegraph (Morse code), continuous wave (CW) code, serial binary code
• Many transmissions are of signals originating in digital forms, then converted to analog for the transmission medium
  • Digital data over the telephone network

Modulation and Multiplexing

• Modulation is converting data into radio waves by adding information to an electronic or optical carrier signal
  • Carriers have constant height/amplitude and frequency
  • Information is added by varying amplitude, frequency, phase, or polarization
• Modulation applies to electromagnetic signals (radio waves, lasers/optics, computer networks)
• Modulation applies to direct current by turning it on/off (Morse code)
• Baseband Transmission: baseband information sent directly/unmodified or used to modulate a carrier
  • Voice placed on wires in telephone/intercom systems
  • Digital signals applied directly to coaxial/twisted-pair cables
• Broadband Transmission: Carrier signal modulated, amplified, sent to antenna
  • Carriers are high-frequency signals modulated by audio, video, or data
  • Radio-frequency (RF) wave: electromagnetic signal able to travel long distances

Common Modulation Methods

• Amplitude Modulation (AM)
• Frequency Modulation (FM)
• Phase Modulation (PM): varying phase angle of sine wave

Frequency-shift keying (FSK)

• FSK converts data to frequency-varying tones
• Modems translate data from digital to analog and back

Demodulation

• Demodulation or detection occurs in the receiver when the original baseband signal is extracted

Multiplexing

• Multiplexing combines multiple signals into one over a shared medium or channel
• Analog signals = Analog Multiplexing
• Digital signals = Digital Multiplexing
• Three types of multiplexing: frequency, time, and code division

Electromagnetic Spectrum

• The electromagnetic (EM) spectrum is the range of all EM radiation types:
  • Includes radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays
• A wave is a vibration in space/time that transfers energy in a repetitive pattern

Wave Components and Parameters

• Crest/Peak: Highest point of wave
• Trough: Lowest point of wave
• Wavelength: Distance between identical points on adjacent cycles, represented by lambda (λ)
• Amplitude: Height of wave above center line, known as rest position
• Frequency: Number of cycles of a repetitive wave, measured in Hertz (Hz)

Wave Period

• Wave Period is the time it takes to complete one cycle
• High-frequency signals have short wavelengths and short periods
• Low-frequency signals have long wavelengths and long periods
• Frequency, Wavelength, and Period Relationships:
  • f = C/λ
  • λ = C/f
  • f = 1/t
  • Where: f = frequency; λ = wavelength; t = period; and c = speed of light

Bandwidth

• Bandwidth (BW) is a range of frequencies occupied by a modulated radio-frequency signal, usually in hertz or as a percentage
• Channel bandwidth is the range needed to transmit information
• Bandwidth is generally limited to -3dB attenuation of max output
• Bandwidth Formula: BW = fH - fL

Communication Applications Survey

• Simplex: AM/FM broadcasting, digital/cable TV, facsimile, wireless remote control, paging, navigation, telemetry, radio astronomy, surveillance, music, internet radio/video
• Duplex: Telephones, two-way radio, radar, sonar, amateur radio, citizens radio, family radio, the Internet, wide-area/metropolitan-area/local area networks
• The entire frequency spectrum between 30 kHz and 300 MHz is spoken for
• The electromagnetic spectrum is a precious natural resource

Careers in Communication Industry

• The electronics industry divides into communications, computers, industrial controls, and instrumentation
• Communications is the largest in terms of employment and equipment value
• Technical Sales Representatives: Determine needs, write proposals, and sell equipment
• Technical Writers: Generate documentation for equipment/systems
• Trainers: Develop training programs/materials for classroom training
• Major employers include manufacturers, resellers, service organizations, and end users