Communication Systems: Elements, Waves, and Signals

Elements of a Communication System

Message: This is information that has meaning for both the sender and the recipient (sender, channel, and receiver).

Bandwidth of a Channel: An indicator of the maximum amount of data that can pass through a communication path at any given time.

Twisted Pair Cable: This is formed by two wire coils.

Coaxial Cable: A copper wire surrounded by a layer of insulating material.

Fiber Optic: This consists of a core and a filament, either glass or plastic, but with different properties.

Atmosphere: This is susceptible to interference and unwanted eavesdropping.

Water: A medium through which ultrasound is propagated.

Outer Space: A medium using radio signals that transmit and receive via satellites.

Waves

Wave: A disturbance that propagates through space, transporting energy.

Mechanical Waves: These need a medium (solid, liquid, or gas) to spread.

Electromagnetic Waves: These travel through a vacuum.

Wave Magnitudes

• Period (T): Repetition time between pulses.
• Wavelength: Distance between two consecutive points.
• Frequency (f): Number of times that the wave is repeated.
• Wave Propagation Speed (v): v = f

Sound is produced when a body vibrates inside air, water, or another natural environment.

Electromagnetic Waves: An electric charge is one in which there is a disturbance; it propagates in a straight line.

Telecommunication Devices

Telephone: This is a device consisting of two energy transducers: the microphone, which transforms sound vibrations, and a headset, which performs the inverse transformation.

The Cordless Phone: This is formed by the base unit and a handheld receiver.

• Base Unit: Connects to a conventional telephone line and an external power source.
• Handheld Receiver: The phone itself does not need a cable and is the main part of the phone, with a rechargeable battery.

Mobile Phone: This is a radio that, to communicate with another phone, uses two different radio frequencies: one to speak and another to hear. It is comprised of a microphone, receiver, liquid crystal display, keypad, antenna, and circuit. It is called a cell phone in every location.

Signal Modulation and Transmission

Modulation: The process by which we transform a signal into another, more complex one. The simplest is that which varies the duration, and another more elaborate one is transmitted by a medium.

Modulating Signal: The one that contains the information to be transmitted.

Carrier Signal: The electromagnetic signal that is to be amended, taking into account the modulating signal.

Amplitude Modulation: Changes the amplitude of the carrier signal.

Frequency Modulation: Determines the frequency of the carrier signal.

Sending and Receiving Signals

The waves emitted into space are captured by the antenna of the radio receiver, such that this is coupled with an oscillating circuit. From here, the signal passes to a detector that splits the wave, which is reproduced by the speaker.

Radio-Space: A transmitter station that can be tuned to occupy a particular place.

Sending and Receiving TV Signals

• TV Over the Air: It transmits a wave but with a higher radio frequency that can be UHF or VHF.
• Cable TV: The broadcast comes through a coaxial cable.
• Satellite TV and Internet: (Satellite) You need a satellite dish and a signal modulator device. (Internet) The signal is received by telephone; it is interactive.