1. ELECTRONIC COMMUNICATION

2. Electronic Communication  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

3. 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

4. Transmitting & Receiving Systems  Telephone –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

5. 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

6. 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

7. 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

8. 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

9. 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