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Introducing communications. What types of communications technology can you think of?. How is information sent?. Telecommunications involves sending, receiving and storing information, which can be sound, images or computer data.
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Introducing communications What types of communications technology can you think of?
How is information sent? Telecommunications involves sending, receiving and storing information, which can be sound, images or computer data. In all communications technology, information is sent (transmitted) as signals. There are two types of signals – analogue and digital. These can be transmitted by wires, radio waves or optical fibres.
voltage time What is an analogue signal? Most of the signals sensed by humans are analogue signals. Everyday examples include sound, light and temperature. An analogue signal may have any value within a continuous range. An analogue signal can be converted into an electrical signal. This graph shows how the voltage of an analogue signal varies with time.
The earpiece/speaker turns analogue electrical signals back into sound waves. The microphone in a telephone mouthpieces turns sound waves into analogue electrical signals. What is an analogue signal? Analogue signals can be sent directly down a copper wire or turned into radio waves. Originally, all telephone and television signals travelled as analogue signals.
current time What is a digital signal? Modern communication systems carry information from analogue signals as digital signals. A digital signal only contains two values: ‘0’(off) and ‘1’ (on). These are used to encode analogue information. Unlike analogue, a digital signal does not vary smoothly, and so is described as being a discontinuoussignal. Digital signals can be sent as electrical signals, radio waves or as pulses of light through optical fibres.
More information. Digital signals can carry more information than analogue signals. For example, digital signals can carry more television and radio stations and ‘interactive’ services. What are the advantages of digital signals? Most forms of communication, such as television and radio, now involve digital signals. This is because digital signals have two main advantages over traditional analogue signals. • No loss of signal quality. Analogue signals lose quality during transmission but digital signals are received unchanged, so there is no loss of information.
original attenuated amplified Why do analogue signals lose quality? All types of signals lose strength as they travel. This is called attenuation and means that signals often have to be amplified so they can be used. Signals can also pick up noise (interference). Amplifying an analogue signal also amplifies the noise. It is difficult to distinguish the noise from the signal, because an analogue signal can have any value. This means that an analogue signal is of lower quality by the time it is received.
original attenuated amplified regenerated Why don’t digital signals lose quality? Digital signals also lose strength and need to be amplified. threshold During transmission, a digital signal can be regenerated by comparing the amplified signal to a threshold value. It is easy to distinguish the noise from a digital signal and so the signal does not lose quality by the time it is received.
What is analogue and digital storage? The terms ‘analogue’ and ‘digital’ do not just apply to the different types of signals that can be used to send information. They also refer to the different methods used for storing and retrieving information. Vinyl records and video tapes are examples of analogue storage. Most modern methods of storing data are digital, such as CDs, DVDs and hard drives.
What are optical fibres? Optical fibres are thin strands of solid glass, about the width of a human hair. Light can travel along an optical fibre, even if it is bent. The light is reflected internally and detected at the other end. Light transmitted through an optical fibre is reflected internally about 6,000 times per metre. In telecommunications, information is encoded as digital signals in the form of pulses of visible or infrared light and transmitted along optical fibres at almost the speed of light. A single optical fibre can carry the digital signals for about 12,000 phone calls, all at the same time!
What are the advantages of optical fibres? Optical fibres are increasingly being used for communications instead of traditional copper wires. Optical fibres have a number advantages over copper wires: • They are cheaper. • They are thinner and lighter. • Signals can travel further. • Not affected by electromagnetic signals so no interference. • Several digital signals can be carried by one fibre. • Signals do not weaken as much while they travel. • More secure – they are almost impossible to bug.
optical fibre messages on different wavelengths sections of messages sent at different times Why don’t messages get mixed up? Multiplexing is the method that allows lots of messages to be sent at the same time without getting muddled up. There are two main types of multiplexing: • Wavelength division • Each message is sent using • a different wavelength. • The receiver tunes into the wavelength of each message. • Time division • Each message is divided into chunks for transmission. • The messages are put back together at the other end.
Optical fibres – the downsides? Optical fibres have changed the way people work and play, but is this necessarily a good thing? Should we be able to get films and music online for free? Can working faster and dealing with more information increase stress at work? Does having books and articles available on computers make it easier for students to cheat?
transmitter receiver Using radio waves in communications Different types of radio waves are used to transmit signals for radio, TV, mobile phones, Wi-Fi and satellite communications. In a transmitter, sound waves are turned into oscillating current, which is then turned into radio waves in an aerial. In a receiver, radio waves are picked up by another aerial, turned back into oscillating current, and then back into sound waves. aerial radio waves
ionosphere Why do some radio waves travel so far? Low frequency (up to 3MHz) radio waves travel along the Earth’s surface and can travel hundreds of miles. These ground waves are used for local and national radio. Higher frequency radio waves (3–30MHz) are reflected off the ionosphere high in the atmosphere. These sky waves are used for international and amateur radio.
ionosphere Microwaves and satellite communications Microwaves are very high frequency radio waves (over 30MHz). Unlike other radio waves, they are not reflected by the ionosphere but pass straight through and into space. This means that they can be picked up by satellites and transmitted over very large distances right round the Earth.
What is a wireless network? A wireless network allows computers, mobile phones and other devices to access the internet and communicate with each other without wires. Wireless technology, sometimes called Wi-Fi, uses high-frequency radio waves (around 2.4 GHz) to transmit data. A Wi-Fi device can connect to the internet via an access point. The region covered by an access point is a ‘hotspot’. Although Wi-Fi is convenient, it can be less secure than a wired network and has a limited range, usually around 100m.
Glossary • amplification – Increasing the strength of a signal. • analogue –A signal with continuously varying intensity. • attenuation – The loss of strength of a signal during transmission. • digital –A signal with only two states; ‘on’ and ‘off’. • encoding –The process of turning an analogue signal into a digital signal. • multiplexing –Sending multiple digital signals at the same time. • optical fibres –Long, thin strands of glass or plastic used to carry digital signals as pulses of infrared or light. • telecommunications – Sending, receiving and storing data via wires, radio waves or optical fibres.
Introducing communications What types of communications technology can you think of?
