introducing communications

3 of 35 © Boardworks Ltd 2006

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.


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.

time

volt

age


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.

The microphone in a telephone mouthpieces turns sound waves into analogue electrical signals.

The earpiece/speaker turns analogue electrical signals back into sound waves.


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 discontinuous signal.

Digital signals can be sent as electrical signals, radio waves or as pulses of light through optical fibres.

time

curr

ent


Converting analogue to digital


What are the advantages of digital signals?

Most forms of communication, such as television and radio, now involve digital 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.

This is because digital signals have two main advantages over traditional analogue signals.

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.


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.

original attenuated amplified

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.

Amplifying an analogue signal also amplifies the noise.

Signals can also pick up noise (interference).


Why don’t digital signals lose quality?

Digital signals also lose strength and need to be amplified.

During transmission, a digital signal can be regenerated by comparing the amplified signal to a threshold value.

attenuated amplifiedoriginal

regenerated

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.

threshold


Analogue or digital?


Communications – matching activity


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.


Opinions on analogue and digital


Optical fibres are thin strands of solid glass, about the width of a human hair.

What are optical fibres?

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.

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.

A single optical fibre can carry the digital signals for about 12,000 phone calls, all at the same time!


What’s in a cable of optical fibres?


How do messages travel along optical fibres?


Sending messages


Optical fibres are increasingly being used for communications instead of traditional copper wires.

They are cheaper.

What are the advantages of optical fibres?

Optical fibres have a number advantages over copper wires:

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.


Multiplexing is the method that allows lots of messages to be sent at the same time without getting muddled up.

Time divisionEach message is divided into chunks for transmission.The messages are put back together at the other end.

Wavelength divisionEach message is sent using a different wavelength.The receiver tunes into the wavelength of each message.

Why don’t messages get mixed up?

optical fibre

messages on different wavelengths

sections of messages sent at different times

There are two main types of multiplexing:


Optical fibres – true or false?


Optical fibres have changed the way people work and play, but is this necessarily a good thing?

Can working faster and dealing with more information increase

stress at work?

Should we be able to get films and music online for free?

Does having books and articles available on computers make it

easier for students to cheat?

Optical fibres – the downsides?


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.

transmitter receiver

aerial radio waves


Why do some radio waves travel so far?

Higher frequency radio waves (3–30 MHz) are reflected off the ionosphere high in the atmosphere. These sky waves are used for international and amateur radio.

Low frequency (up to 3 MHz) radio waves travel along the Earth’s surface and can travel hundreds of miles. These ground waves are used for local and national radio.

ionosphere


Microwaves and satellite communications

Microwaves are very high frequency radio waves (over 30 MHz).

This means that they can be picked up by satellites and transmitted over very large distances right round the Earth.

Unlike other radio waves, they are not reflected by the ionosphere but pass straight through and into space.

ionosphere


What’s the frequency, Kevin?


A wireless network allows computers, mobile phones and other devices to access the internet and communicate with each other without wires.

What is a wireless network?

Although Wi-Fi is convenient, it can be less secure than a wired network and has a limited range, usually around 100 m.

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’.


Why is my laptop wireless enabled?


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.


Anagrams


Multiple-choice quiz


Introducing communications

What types of communications technology can you think of?

introducing communications

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