Duncanrig Secondary School
East Kilbride
S3 Physics Elective
Telecommunications
Activity Booklet
S3 Physics Elective / TelecommunicationsINSTRUCTIONS: Always put today’s date and copy each HEADING carefully.
A good scientist always dates their work. Your jotter will form a complete set of notes on Telecommunications. It is important that you keep a useful record of work in your jotter. Full sentence answers are required for questions and experiments should be fully written up with a conclusion checked by your teacher. If you are off it is your responsibility to ‘catch up’. Speak to your teacher or friends to find out what you missed and get a copy.
Symbols used in this booklet:
Copy
The little pencil symbol means that you copy the passage neatly into you Physics Jotter. It is important that the Copy Passages are copied accurately since the content may appear in the End of Unit Test.
Read
The little book symbol means that you must read the passage carefully so you can extract the required information and so that knowledge is gained for the test.
What to do
This little symbol means you must collect apparatus and carry out an experiment OR follow instructions in an activity. Remember, apparatus may be delicate and costly and should be treated as such. Please return all apparatus to its appropriate place of storage.
Questions Answer in full sentences
This little question symbol means that there are some questions to be answered as best as you can. If you are unsure of an answer, your teacher may help or you can find out the answer from other sources like a text book or internet. A full sentence answer means you can tell what the question was from reading the answer.
More to do
The plus sign means that if you have the time there is more work that can be done.
Watch a video
This symbol means that your teacher may show you a short video clip.
See something on the internet
Your teacher may show you something on the internet to help your understanding.
TELECOMMUNICATIONS
HEADING Activity 1 Constructing a Title Page
Start this Telecommunications Unit with a Title Page.
A title page should contain both text and graphics.
Use colours where possible. Here is an example:
HEADING Activity 2 Introducing Telecommunications
Read
Telecommunications (sometimes shortened to Telecoms) is about transmitting information over long distances. There are five members of the Electromagnetic Spectrum used in Telecommunications: Visible Light, Infrared, Microwave, Television and Radio. Signals, carrying information, can travel through the air/vacuum as waves, through optical fibres as light and through copper wiring as electrical signals.
Questions Answer in full sentences
1. Write down as many ways you can think of that we transmit information over long distances in this modern age of electricity and electronics.
2. Consider now earlier times before the modern age of electricity and electronics, how did people send information over long distances then?
3. What type of Electromagnetic Radiation do you think is required for each of your answers to Q1?
4. What three things can signals travel through to reach their destination?
More to do
Collect a set of cards showing some telecommunications methods and put them in order from oldest to newest. In your jotter estimate the year when they were first used. (Your teacher will run through the timeline)
HEADING Activity 3 Analogue Radio Transmission
Read
At the time of writing, radio stations in the UK transmit analogue and digital signals (we will discuss the difference in Activity 5). In order to receive these signals you need a radio receiver (in days gone by these were sometimes referred to as a ‘wireless’ as the signal did not come down a wire). If you want to receive digital radio you need a DAB (Digital Audio Broadcasting) radio receiver (these will also pick up analogue signals). However, an analogue receiver will not pick up digital radio. The changeover from analogue to digital TV happened in 2011. At the time of writing, 2015 is the proposed date for the changeover from analogue to digital radio, however, the following actions will need to be achieved before the changeover:
• National DAB digital radio coverage to be comparable to FM coverage;
• Local DAB digital radio to reach 90% of the population and all major roads;
• A range of DAB digital radios to be on sale for less than £20;
• The majority of car radios to be converted to digital; and
• 50% of listening to be to digital.
Analogue Transmission
The block diagram shows the basic parts required to transmit radio signals. The radio frequency (that’s the one you tune in to with your radio receiver e.g. Radio 1 broadcasts on the frequency range 97.7 MHz to 99.7 MHz F.M., that’s 97 700 000 – 99 700 000 Hz). The audio signal is a much lower frequency in the range of human hearing (20 – 20 000 Hz). This is the DJ’s voice and the music played. The modulator combines these two signals which are then amplified before being transmitted by the aerial. The signal can only travel so far before it needs amplified again. There are two different ways that the signal can be modulated – A.M. amplitude modulation and F.M. frequency modulation. Look at the diagrams below to see the difference.
This is the audio signal
This is the high frequency radio wave, sometimes called the carrier wave
This is the amplitude modulated (A.M.) signal. The amplitude of the radio wave has been altered by the audio signal
This is the frequency modulated (F.M.) signal. The frequency of the radio wave has been altered by the audio signal
Sending information by changing the shapes of waves is an example of an analogue process.
What to do
Watch the demonstration of the amplitude modulated signal.
More to do
Look at the signals below and answers the following questions:
1. Which signals show audio waves?
2. Which signal shows a radio wave?
3. Which signals show amplitude modulated waves?
4. Which signal shows a frequency modulated wave?
5. Match the amplitude modulated waves to the audio signal they are carrying.
6. Match the radio wave to the correct amplitude modulated wave.
a /
b
c /
d
e /
f
HEADING Activity 4 Analogue Radio Reception
Read
It’s is more than likely that all of you have used an analogue radio receiver. You may have got to use one during the Electromagnetic Spectrum topic. To carry out the job of receiving the signal and ultimately allow you to hear the radio broadcast, analogue radio receivers are built from six main parts. You can probably name some of these already? The aerial picks up all the radio signals transmitted, from every radio station within range. After this point the signal is an electrical signal. The tuner selects the desired frequency, so if you want to listen to Radio 1 you need tune to 97-99 MHz on FM (remember FM from Activity 3). The tuner may be a dial or push button. The signal may have been sent as AM or FM:
AM / FMThe decoder is a device which separates the audio signal from the modulated signal. We no longer need the radio signal that was carrying it once it has got to the radio receiver. The audio signal is weak. In order to make it stronger we use an amplifier. The amplifier requires a power source e.g. a battery or mains supply. Finally, we are ready to listen to the audio signal through the loudspeaker. The loudspeaker converts the electrical signal into sound waves.
What to do
1. Watch the demonstration of the various parts that make up the radio receiver.
2. Ensure that all the words in bold and their meanings are copied into your jotter.
3. Complete the block diagram of the radio receiver below with the six parts.
4. The wave diagrams, shown over the page, do not match the correct stage of journey. Can you match them correctly?
Wave diagrams / Stage of journeya / / Received by the aerial
b / / Selected by the tuner
c / / A decoded signal
d /
/ An amplified decoded signal
e / / An audio wave
HEADING Activity 5 Analogue and Digital Signals
Read
Sound, like your voice, is an example of an analogue signal. As you speak, your voice contains lots of different frequencies at lots of different amplitudes. A digital signal is just a sequence of ones and zeros. A simple “modem” which sends data from your computer down the phone line may use two notes, one high and one low, representing a “1” and a “0”, so that a sequence of these notes represents a stream of “1”s and “0”s. Flashes of light are another example of a digital signal, where “on” is a “1” and “off” is a “0”. An analogue signal is relatively simple to “hear” or understand, whereas a digital signal must be “decoded” in some way before it is understandable.
Analogue Signal / Digital SignalWatch a video
Your teacher may show you a video to help to explain analogue and digital (http://www.bbc.co.uk/learningzone/clips/6018.html).
HEADING Activity 6 Converting Analogue to/from Digital
Read
To convert from an analogue signal to a digital signal requires an analogue to digital converter. An analogue to digital converter understands decimal and binary numbers. The video showed that an analogue wave can be converted to digital by sampling the values on the analogue wave and converting them to binary numbers.
Analogue Signal / Digital SignalThe decimal number 8 is 1000 and the decimal number 6 is 110 so together these form a digital wave pattern of 1000110 shown in the second diagram. The higher the sample rate the better quality the digital signal. In decimal numbers the right most value represents the number of units, the next along the number of 10s, the next again 100s and so on. The values can range from 0 to 9.
1000s / 100s / 10s / units4 / 2 / 3 / 5
So the number above is (4 x 1000) + (2 x 100) + (3 x 10) + (5 x 1) = 4235. When you were first learning to read larger numbers this is probably how you had to think about it.
In binary the right most value represents the number of units, the next along the number of 2s, the next again 4s and so on. The values can range from 0 to 1.
8s / 4s / 2s / units1 / 0 / 0 / 1
So the number above is (1 x 8) + (0 x 4) + (0 x 2) + (1 x 1) = 9 in decimal.
Your teacher will show you how to convert 1010, 1011 and 1100 to decimal on the board.
What to do
Follow the example above and the examples from your teacher and convert the following binary numbers from binary to decimal.
1. 1000 / 2. 0001 / 3. 0011 / 4. 00005. 0100 / 6. 0111 / 7. 0110 / 8. 0101
More to do
You now should know all the numbers 0 – 12 in binary form. Use this information to convert the analogue signals, (a) and (b) below, to digital signals. Convert the decimal numbers to binary and then draw the digital signal on a grid (looking back at the previous page may help).
(a) / (b)
HEADING Activity 7 Digital Radio Transmission and Reception
Read
Unlike analogue radio, digital radio sends speech and songs through the air as strings of numbers. Digital technology also brings many more stations and displays information about the program you're listening to (such as the names of music tracks or programs). Digital radio works by breaking the program to be broadcast into fragments (small bits) and coded into numbers (1s and 0s that form binary numbers that relate to the analogue signal - just like you saw in Activity 6). The transmitter sends out each fragment many times to increase the chances of it getting through. Even when things interrupt or delay some of the fragments, the receiver can still piece together fragments arriving from other places and put them together to make an uninterrupted program signal. To help avoid interference, a digital radio signal travels on a huge, broad band of radio frequencies about 1500 times wider than those used in analogue radio. If you put a digital radio and an ordinary analogue radio next to one another and turn them both on together, you'll find the sound from the digital radio lags noticeably behind the sound from the analogue radio because of the time it takes to reassemble the digital signal. In order to receive digital radio, a digital radio receiver is required and at the time of writing these are more expensive than analogue sets. In addition, some areas of the country cannot receive digital radio at present. Analogue radio is more prone to interference. As you move away from the transmitting site the signal gets weaker.
What to do
1. On your copy of the above text underline any advantages digital radio has over analogue radio. Select a coloured pencil to do so.
2. On your copy of the above text underline any disadvantages of digital radio. Select a different coloured pencil to do so.
3. Include a key for the colours you have used.
4. Glue the passage into your jotter.
HEADING Activity 8 Switching Over from Analogue to Digital
Copy
In the year 2011 the UK stopped transmitting TV signals in analogue and switched fully over to transmitting in digital.