XII.XV Communication Systems

Communication is the act of transmission of information. Every communication system has 3 essential elements:

• Transmitter
• Channel
• Receiver

There are two basic modes of communication:

• Point to point e.g; telephony
• Broadcast e.g; radio, television

Modern communication has its root in the 19th and 20th century.

• 1835:: Telegraph: Samuel F B Morse, Sir Charles Wheatstone
• 1876:: Telephone: Alexander Graham Bell, Antonio Meucci
• 1895:: Wireless Technology: Jagadis Chandra Bose, Guglielno Marconi
• 1936:: Television Broadcast: John logi Baird
• 1955:: Radiofax: Alexander Bain
• 1968:: ARPANET: J C R Licklider
• 1975:: Fibre Optics: Bell Laboratories
• 1990:: World Wide Web : Tim Berners-Lee

Basic terminology used in electronic communication systems;

• Transducer: Any device that converts one form of energy into another
• Signal: Information converted into electrical form for transmission
• Analog Signals are continuous variation of voltage or current
• Digital Signals are those signals which can take only discrete step wise values e.g; Binary signals {0,1}
• Noise: Unwanted signals from other sources or from inside that tend to disturb the transmission and processing of message signals in a communication system
• Transmitter processes and receiver extracts the message signal through a channel
• Attenuation: The loss of strength of a signal while propagating through a medium
• Amplification is increasing of amplitude/strength of a signal
• Range: Largest distance between a source and destination up to successful transmission
• Bandwidth: Band of frequencies, necessary for satisfactory transmission
• Repeater: A repeater is a combination of a receiver and a transmitter. Repeater are used to extend the range of a communication. In fig. tower 1 is a transmitter, tower 2 is a repeater and tower 3 is a receiver
  
  
  

Wave Types::

• 
• Sky-wave is achieved by ionospheric reflection
• Space wave is used in line of sight communication and satellite communication
• Ground wave glides over the earth as surface current.

Propagation of electromagnetic waves: To radiate signals of high frequency, antennas should have have a size comparable to the the wavelength of the signal (at least wavelength/4)