Transcript ELECTRONIC COMMUNICATION

ELECTRONIC
COMMUNICATION
Electronic Communication
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Three parts : Transmitter, Receiver and Channel
Channel uses electrical energy
Graphic communication + electrical energy
Electronic communication
Information age
Steam engine
Industrial age
Channel can be air or cables
Systems sending messages immediately are Transmitting
and Receiving Systems
 Systems storing messages electronically are Recording
Systems
Transmitting & Receiving
Systems
 Telegraph
– The first electronic communication system
– F. B. Morse built a telegraph line in 1843
– The first telegraph cable was laid across Atlantic
Ocean in 1858
– Telegraph system = Key, Power source, Sounder and
Wires --- Morse Code
Transmitting & Receiving
Systems
 Telephone
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Graham Bell was a teacher of the deaf
A telephone mouthpiece contains tiny carbon grains
Louder speech --- grains are tightly packed
Soft speech --- grains are loosely packed
The amount of the current flow changes as we change
the way we speak
– A thin piece of metal vibrates in the earpiece on the
receiver
– Amplifiers, repeaters are needed for the long distance
transmission to increase the electric current
– Connection b/w two telephone --- Telephone Switching
--- Digital to Analog conversion
Transmitting & Receiving
Systems
 Telephone
– Fiber optic --- 10,000 conversations, Microwave --1000 conversations
– Digital technology --- forwarding, waiting, voice
synthesizer
– Cordless phone --- transmission to a nearby telephone
– Cellular phone --- radio wave --- particular area
– Automatic telephone switching --- Strowger switches
Transmitting & Receiving
Systems
 Radio
– Maxwell --- signals can be sent through air
– Marconi heard the three shorts of the Morse Code for the letter S,
sent across the Atlantic
– Regular radio broadcasts began in the 1920s --- antennas
– Radio lets us listen to music, news and sporting events and also
provides us a mode of two way communication
– Alternating voltage is sent to an antenna --- an electromagnetic
wave is launched into the air
– Low frequency --- high wavelength and vice versa
– Wave length = speed of the wave / frequency of the wave
Transmitting & Receiving
Systems
 Radio
– High frequency (HF) radio waves bounce off the
atmosphere’s upper layer, the ionosphere --- for two
points on the earth
– Super high frequency (SHF) radio waves are used for
satellite communication
– The channel is the part of the electromagnetic spectrum
used for the signal
– One transmitter, many receivers --- broadcasting, e.g.
FM & AM
– One transmitter, one receiver --- point to point
Transmitting & Receiving
Systems
 Television
– Much like the radio except that the transmission can be
seen also
– Video camera is needed at the transmitting station and a
monitor at the receiving station
– Video signals may be stored --- VCR
– Color signals break down light into red, green and blue
– Cable TV, Pay per view
Transmitting & Receiving
Systems
 Microwave Communication
– Microwaves are radio signals that use higher
frequencies than FM radio signals or TV broadcasts
– Used for telephone and TV signal transmission
– Frequency distribution for different uses on page 177
 Satellite Communication
– They are radio relay stations called repeaters
– They have to be geosynchronous
– Uplink and downlink