TELEVISION Diagram: MOBILE PHONES When phone is on, it is constantly checking for incoming calls and looking for the CELL SITE with strongest power. Sound Electrical Radio waves Transmitted via microwaves Electrical energy Sound energy CD PLAYER A physical pattern is recorded as data on a CD “a series of flats and bumps exists on what appears to be a flat disc surface” Photodiode – light energy electrical energy Transmission channel – digital signals are converted from the original signal, amplified and converted to sound by the speaker
Timeline of communication systems/technologies; 1870s – Bell invents the electric telephone 1890s – Portable typewriter is invented 1890s – Marconi invents wireless telegraphy long distance radio communication 1930s – Regular TV broadcasting begins Late 1930s – Atanasoff invents first electronic digital computer 1950s – Laser is invented 1980s – First optical fibre system is created long distance 1990s – Berners-Lee invents the World Wide Web (www) 1990s – VCRs become popular Impact of TWO chosen communication systems on society; Telephone (1876) Simple and fast communication Long distance communication reduces travel time Confidential Quality of communication was improved Versatile e.g. used in businesses, entertainment Electrical computer (late 1930s) Easy communication Convenient to use Used in many industries e.g. technology, multimedia, office helped to create JOBS Easy access and storage of information Improved efficiency and quantity of communication OUTCOME 2 2.4 Perform a first-hand investigation to observe ways in which waves can be modulated to carry different types of information Wave modulation (modification) allows different information to be transmitted. A wave can be modulated in 2 ways; Amplitude modulation (AM) – height of the waves Frequency modulation (FM) – number of waves which pass a point in 1 second Radio transmitter – the coding device In the AM radio transmitter:
One electric circuit produces the audio signal - Sound waves are converted into electrical signals Another circuit creates a carrier signal (function of a carrier wave; to carry info from one place to another as an EM wave) A third circuit creates a modulated signal – i.e. the two previous signals are “added” together The audio signal carries speech and music and has a low, varying frequency. The carrier signal is an electrical signal with a high, constant frequency. Carrier and modulated signal both have a high frequency. OUTCOME 3 3.4 Plan, choose equipment or resources for, and perform a investigation to compare the quality of reception of AM and FM radio waves Background information: AM radio waves Have relatively LOW frequency but LONG wavelengths Long wavelengths allows for AM to diffract (bend around objects) with little loss of energy Useful when broadcast radio waves are needed Travel in straight lines Reflect off a layer of the atmosphere called ionosphere: allows for OUT-OF-SIGHT transmission useful in long distance communication Useful to carry only voice transmissions (quality of sound broadcast is relatively poor) Susceptible to interference e.g. storms can severely affect the quality Advantage – AM circuitry is not overly complicated, cheap and readily available / Disadvantage – crowded with users FM radio waves Have relatively LOW frequency SHORTER wavelengths than AM waves therefore they do not diffract as well objects reduce signal strength Travel in straight lines but spread out from a point source Must be LINE-OF-SIGHT as they do NOT reflect off Carry more information than AM waves higher frequency than AM waves Generally higher quality than AM EXPERIMENT COMPARING FM AND AM Independent variable – type of signal
This happens if the incident angle is GREATER THAN the critical angle. It will only happen when the light is passing from an optically dense medium (glass) to an optically less dense medium (air). When total internal reflection occurs there is NO REFLECTION of light. 6.5 Process and analyse information to compare and contrast copper cables with fibre optic cables in relation to: Carrying capacity Cost Rate of information transfer Security Carrying capacity – optical fibre has greater information carrying capacity than any other medium (including radio, wireless or copper wire) Cost – much greater amounts of information can be transferred at a much lower cost per GB of data to the service provider and consumer. Optical fibre is therefore much cheaper using this criterion. Rate – information transfer via fibre optic cables is significantly faster than copper cables Security – signals in copper wires can be ‘tapped’ more readily than optical fibre signals; copper wires present a greater security risk than optical fibres. SUMMARY