TELECOMMUNICATIONS –Communication over a long distance; deals with devices used to transmit and receive messages over a distance. –Examples: Telegraph Telephones/Cell Phones Television Radio Computers using Internet/ HISTORY OF TELECOMMUNICATION Pre-20 th century methods: Pony Express Smoke and fire signals Visual Telegraphs relayed messages from station to station.

TELEGRAPHS Samuel Morse Sends electrical impulses over wire based on the principles of electromagnetism –Parts: Battery A Key (the sending device) A Wire A Sounder (the receiving device) –Morse Code language (a series of dots and dashes) TELEPHONE Alexander Graham Bell (patented 2 hrs ahead of Elisha Gray) Used the principle that sound waves cause vibrations Modern telephones use integrated circuits (IC’s) to send & receive the message created by the sound waves Cell Phones –Use radio waves to transmit conversations –Calls are transferred to a series of cells to ensure a good signal is maintained –Contain a transceiver (a transmitter and a receiver combined into a single unit). transmitter converts signals into radio waves receiver changes radio waves into electrical signals & sends them to the phone’s control unit

TELEPHONE (cont’d) –Today, all cell phones use today use digital technology. Offers: Better quality voice transmission More service options Digital technology makes it almost impossible to intercept and listen to the conversation, greatly improving security –Personal Communication Services (PCS) was a completely digital cellular technology that made it possible to use 2-way paging, voice messaging, and many other services.

TRANSMISSION CHANNELS Communication channels: paths over which messages must travel to get from the sender to the receiver Examples: –Copper Wire: two thin, insulated copper wires twisted around each other; can be bundled together with other twisted pairs to form large cables; not being used for newly laid cables –Coaxial Cable: has an outer tube made of material that conducts electricity (usually copper); inside is an insulated central conductor; can be bundled; more efficient than twisted-pair –Optical Fibers: thin, flexible fibers of pure glass that carry signals in the form of pulses of light; fiber surrounded by reflective covering and an outside protective covering; much more efficient; much thinner; carries thousands of voice circuits –Microwaves: very short electromagnetic waves; used to carry phone conversations; can be sent and received without the use of any type of wire; billions of microwaves can pass a given point in less than a second. –Radio Waves: also electromagnetic waves, but they are longer than microwaves. All waves have amplitude (the strength of the wave) and frequency (the number of waves that pass a given point in one second). Waves can be modulated by amplitude (AM) or by frequency (FM).

GETTING A MESSAGE TO THE RIGHT PLACE Early Switching Systems: required human operators to connect phones Automated Telephone Exchanges: late 1950’s; use computers to route a calls RADIO 1895 by Guglielmo Marconi; used electromagnetism to send a telegraph message more than 1 mile without using a wire Modulates radio signal’s amplitude or frequency, amplifies signal, antenna sends the signal through the air where another antenna can pick up the signal Digital Technology: Digital Audio Broadcasting (DAB) and Digital Audio Radio (DAR) – high-quality audio signals sent in a digital rather than analog format HD Radio: Hi-Def radio; considered the premier radio signal

TELEVISION Television works on the principles of sending pictures & sounds through the air or over a wire How T.V. works: –T.V. camera: focuses images on a special target surface within a pick-up tube; surface is divided into thousands of pixels; light from televised image gives each pixel an electrical charge; electrons pass through target surface & strike a signal plate, creating an electrical current (this is the electrical video signal that will be transmitted). As the camera picks up and converts the video portion into electrical signals, microphones pick up the audio portion. –Transmission: The audio and video TV signals are amplified, modulated, combined, amplified again, and then sent to a satellite where they are transmitted. –The T.V. Receiver: screen is covered with phosphor salts; electron gun shoots the tube, projecting a beam on the screen; beam energizes the phosphor and makes the pixels glow, creating an image. LED; LCD; Plasma –HDTV: creates cinema-quality audio & video; the number of scanning lines are doubled, meaning the picture screen can be much larger without losing picture sharpness. –Digital T.V.: required in 2009; all signals broadcast using digital signals; digital T.V. sets are (basically) large computer monitors; viewer can manipulate the video images on the screen.

SATELLITE COMM. SYSTEMS A Communication Satellite is a device placed into orbit above the earth to send and receive messages from one place to another, acting as a relay station or “mirror” in the sky. Satellites make it possible to communicate instantly using “real-time” technologies. How the System Works: –Signals are sent to orbiting satellites through an earth station, which is a large, pie-shaped antenna that receives and sends the signal to the satellite. This process is called an uplink. As the satellite receives the signal, it sends the signal back to another station on earth – this process is called a downlink. –Receiving earth stations receive the signal and send them to the desired receiver.