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  • Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10
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Compiled and rearranged by Sajit Chandra Shakya 9702/04/M/J/07 For Examiner’s Use © UCLES 2007 1 An analogue signal is sampled at a frequency of 5.0 kHz. Each sample is converted into a four-bit number and transmitted as a digital signal. Fig. 10.1 shows part of the digital signal. 0010 0101 1010 1111 0100 0010 0101 1010 1111 0100 most significant bit START Fig. 10.1 The digital signal is transmitted and is finally converted into an analogue signal. (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 14 signal 12 10 8 6 4 2 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 t /ms 2.0 [4] Fig. 10.2 (b) Suggest two ways in which the reproduction of the original analogue signal could be improved. 1. ..................................................................................................................................... .......................................................................................................................................... 2. ..................................................................................................................................... ..................................................................................................................................... [2] 1

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Page 1: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

Compil

ed an

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Sajit

Chand

ra Sh

akya

9702/04/M/J/07

ForExaminer’s

Use

© UCLES 2007

1 An analogue signal is sampled at a frequency of 5.0 kHz. Each sample is converted into a four-bit number and transmitted as a digital signal.

Fig. 10.1 shows part of the digital signal.

0010 0101 1010 1111 0100 0010 0101 1010 1111 0100

most significant bit

START

Fig. 10.1

The digital signal is transmitted and is finally converted into an analogue signal.

(a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal.

0 0.2

18

16

14signal

12

10

8

6

4

2

00.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

t /ms

2.0

[4]

Fig. 10.2

(b) Suggest two ways in which the reproduction of the original analogue signal could be improved.

1. .....................................................................................................................................

..........................................................................................................................................

2. .....................................................................................................................................

..................................................................................................................................... [2]

1

Page 2: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Sajit

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9702/04/M/J/07© UCLES 2007

2 (a) Fig. 11.1 is a block diagram showing part of a mobile phone handset used for sending a signal to a base station.

aerial

microphone

Fig. 11.1

Complete Fig. 11.1 by labelling each of the blocks. [3]

(b) Whilst making a call using a mobile phone fitted into a car, a motorist moves through several different cells. Explain how reception of signals to and from the mobile phone is maintained.

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ForExaminer’s

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2

Page 3: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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9702/04/M/J/08

ForExaminer’s

Use

© UCLES 2008

3 (a) (i) Describe what is meant by frequency modulation.

..................................................................................................................................

..................................................................................................................................

.............................................................................................................................. [2]

(ii) A sinusoidal carrier wave has frequency 500 kHz and amplitude 6.0 V. It is to be frequency modulated by a sinusoidal wave of frequency 8 kHz and amplitude 1.5 V.

The frequency deviation of the carrier wave is 20 kHz V–1. Describe, for the carrier wave, the variation (if any) of

1. the amplitude,

..................................................................................................................................

.............................................................................................................................. [1]

2. the frequency.

..................................................................................................................................

..................................................................................................................................

..................................................................................................................................

.............................................................................................................................. [3]

(b) State two reasons why the cost of FM broadcasting to a particular area is greater than that of AM broadcasting.

1 .......................................................................................................................................

..........................................................................................................................................

2 .......................................................................................................................................

...................................................................................................................................... [2]

3

Page 4: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Sajit

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9702/04/M/J/08

ForExaminer’s

Use

© UCLES 2008

4 (a) Optic fibre transmission has, in some instances, replaced transmission using co-axial cables and wire pairs.

Optic fibres have negligible cross-talk and are less noisy than co-axial cables. Explain what is meant by

(i) cross-talk,

..................................................................................................................................

..................................................................................................................................

.............................................................................................................................. [2]

(ii) noise.

..................................................................................................................................

..................................................................................................................................

.............................................................................................................................. [2]

(b) An optic fibre has a signal attenuation of 0.20 dB km–1. The input signal to the optic fibre has a power of 26 mW. The receiver at the output of

the fibre has a noise power of 6.5 µW. Calculate the maximum uninterrupted length of optic fibre given that the signal-to-noise

ratio at the receiver must not be less than 30 dB.

length = ........................................... km [5]

4

Page 5: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Chand

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9702/04/M/J/09© UCLES 2009

ForExaminer’s

Use

5 A signal is to be transmitted along a cable system of total length 125 km. The cable has an attenuation of 7 dB km–1. Amplifiers, each having a gain of 43 dB, are placed

at 6 km intervals along the cable, as illustrated in Fig. 12.1.

6km 6km amplifiergain 43 dB

6km

125km

outputsignal

inputsignal

450 mW

Fig. 12.1

(a) State what is meant by the attenuation of a signal.

..........................................................................................................................................

.................................................................................................................................... [1]

(b) Calculate

(i) the total attenuation caused by the transmission of the signal along the cable,

attenuation = ......................................... dB [1]

(ii) the total signal gain as a result of amplification by all of the amplifiers along the cable.

gain = ......................................... dB [1]

5

Page 6: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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akya

9702/04/M/J/09© UCLES 2009

ForExaminer’s

Use

(c) The input signal has a power of 450 mW. Use your answers in (b) to calculate the output power of the signal as it leaves the cable system.

power = ....................................... mW [3]

6

Page 7: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Chand

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9702/04/M/J/09© UCLES 2009

ForExaminer’s

Use

6 (a) Fig. 13.1 is a block diagram illustrating part of a mobile phone handset used for receiving a signal from a base station.

D A C

switch

Fig. 13.1

Complete Fig. 13.1 by labelling each of the blocks. [4]

(b) Explain the role of the base station and the cellular exchange when a mobile phone is switched on and before a call is made or received.

..........................................................................................................................................

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..........................................................................................................................................

..........................................................................................................................................

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..........................................................................................................................................

..........................................................................................................................................

.................................................................................................................................... [4]

7

Page 8: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Sajit

Chand

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akya

9702/04/O/N/07

ForExaminer’s

Use

© UCLES 2007

7 Fig. 10.1 shows the variation with frequency f of the power P of a radio signal.

0 45 50 55

f / kHz

P

Fig. 10.1

(a) State the name of

(i) the type of modulation of this radio signal,

..............................................................................................................................[1]

(ii) the component of frequency 50 kHz,

..............................................................................................................................[1]

(iii) the components of frequencies 45 kHz and 55 kHz.

..............................................................................................................................[1]

(b) State the bandwidth of the radio signal.

bandwidth = ...........................................kHz [1]

(c) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of the signal voltage of Fig. 10.1.

20 0

signal voltage

40 60 80 120 140 160 180 200 220 t / µs

100 0

[3]

Fig. 10.2

8

Page 9: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Chand

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akya

9702/04/O/N/07

ForExaminer’s

Use

© UCLES 2007

8 In a cellular phone network, a country is divided into a number of cells, each with its own base station.

Fig. 11.1 shows a number of these base stations and their connection to a cellular exchange.

cellularexchange

cell

basestation

Fig. 11.1

(a) Suggest and explain why the country is divided into a number of cells.

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

......................................................................................................................................[2]

(b) Outline what happens at the base station and the cellular exchange when a mobile phone handset is switched on, before a call is made.

..........................................................................................................................................

..........................................................................................................................................

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......................................................................................................................................[4]

9

Page 10: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Sajit

Chand

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9702/04/O/N/08© UCLES 2008

ForExaminer’s

Use

9 Different frequencies and wavelengths are used in different channels of communication. Suggest why

(a) infra-red radiation rather than visible light is usually used with optic fibres,

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [2]

(b) the base stations in mobile phone networks operate on UHF,

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [2]

(c) for satellite communication, frequencies of the order of GHz are used, with the uplink having a different frequency to the downlink.

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [2]

10

Page 11: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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9702/41/O/N/09© UCLES 2009

ForExaminer’s

Use

10 (a) State and explain two advantages of the transmission of information in digital, rather than analogue, form.

1. .....................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

2. ......................................................................................................................................

..........................................................................................................................................

.......................................................................................................................................... [4]

(b) Convert

(i) the decimal number 13 to a four-bit digital number,

............................................................................................................................ [1]

(ii) the digital number 0101 to a decimal number.

............................................................................................................................ [1]

(c) An analogue signal is to be transmitted digitally. A block diagram for part of the transmission system is shown in Fig. 12.1.

ADCanalogue

signalrecoveredanalogue

signal

parallelto

serialconverter

block X

transmission

block Y

Fig. 12.1

(i) Complete Fig. 12.1 by labelling block X and block Y. [2]

(ii) State the purpose of the parallel-to-serial converter.

..................................................................................................................................

..................................................................................................................................

............................................................................................................................ [2]

11

Page 12: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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9702/41/O/N/09© UCLES 2009

ForExaminer’s

Use

(d) The original analogue signal is shown in Fig. 12.2. The recovered signal after transmission is shown in Fig. 12.3.

signal

00 time

recoveredsignal

00 time

Fig. 12.2 Fig. 12.3

Suggest and explain two ways in which the reproduction of the input signal may be improved.

1. ......................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

2. ......................................................................................................................................

..........................................................................................................................................

.......................................................................................................................................... [4]

12

Page 13: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Chand

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9702/42/O/N/09

ForExaminer’s

Use

© UCLES 2009

11 The variation with time of the signal transmitted from an aerial is shown in Fig. 11.1.

00

1020

3040

5060

7080

9010

011

012

013

014

015

016

017

018

019

020

0tim

e / l

s

sign

alvo

ltage

Fig

. 11.

1

13

Page 14: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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Sajit

Chand

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akya

9702/42/O/N/09© UCLES 2009

ForExaminer’s

Use

(a) State the name of this type of modulated transmission.

.................................................................................................................................... [1]

(b) Use Fig. 11.1 to determine the frequency of

(i) the carrier wave,

frequency = ........................................... Hz [2]

(ii) the information signal.

frequency = ........................................... Hz [1]

(c) (i) On the axes of Fig. 11.2, draw the frequency spectrum (the variation with frequency of the signal voltage) of the signal from the aerial. Mark relevant values on the frequency axis.

frequency

signalvoltage

Fig. 11.2[3]

(ii) Determine the bandwidth of the signal.

bandwidth = ........................................... Hz [1]

14

Page 15: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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akya

9702/42/O/N/09© UCLES 2009

ForExaminer’s

Use

12 A block diagram representing part of a mobile phone network is shown in Fig. 12.1.

X

X

X Y

PublicSwitchedTelephoneNetwork(PSTN)

X

X

mobile phonehandset

Fig. 12.1

(a) State what is represented by

(i) the blocks labelled X,

............................................................................................................................ [1]

(ii) the block labelled Y.

............................................................................................................................ [1]

(b) A user of a mobile phone is making a call.

Explain the role of the components in the boxes labelled X and Y during the call.

..........................................................................................................................................

..........................................................................................................................................

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© UCLES 2009

15

Page 16: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

Compiled and re

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ajit Chandra Shakya

9702/43/M/J/10© UCLES 2010

ForExaminer’s

Use

13 A telephone link between two towns is to be provided using an optic fibre. The length of the optic fibre between the two towns is 75 km.

(a) State two changes that occur in a signal as it is transmitted along an optic fibre.

1. ......................................................................................................................................

..........................................................................................................................................

2. ......................................................................................................................................

.......................................................................................................................................... [2]

(b) The optic fibre has an attenuation per unit length of 1.6 dB km–1. The minimum permissible signal-to-noise power ratio in the fibre is 25 dB. The average noise power in the optic fibre is 6.1 × 10–19 W.

(i) Suggest one reason why power ratios are expressed in dB.

..................................................................................................................................

............................................................................................................................ [1]

(ii) The signal input power to the optic fibre is designed to be 6.5 mW. Determine whether repeater amplifiers are necessary in the optic fibre between the

two towns.

[5]

Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.

University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

Page 17: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

Compiled and re

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ajit Chandra Shakya

9702/41/M/J/10© UCLES 2010

ForExaminer’s

Use

14 Many radio stations now broadcast on FM rather than on AM. In general, FM is broadcast at much higher frequencies than AM.

(a) Explain what is meant by FM (frequency modulation).

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [2]

(b) State two advantages and two disadvantages of FM transmissions when compared with AM transmissions.

advantages of FM transmissions

1. .....................................................................................................................................

..........................................................................................................................................

2. .....................................................................................................................................

..........................................................................................................................................

disadvantages of FM transmissions

1. .....................................................................................................................................

..........................................................................................................................................

2. .....................................................................................................................................

.......................................................................................................................................... [4]

Page 18: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

Compiled and re

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ajit Chandra Shakya

9702/41/M/J/10© UCLES 2010 [Turn over

ForExaminer’s

Use

15 A ground station on Earth transmits a signal of frequency 14 GHz and power 18 kW towards a communications satellite orbiting the Earth, as illustrated in Fig. 12.1.

Earth

ground station,signal power18 kW

satellite

signal frequency

14 GHz

Fig. 12.1

The loss in signal power between the ground station and the satellite is 190 dB.

(a) Calculate the power of the signal received by the satellite.

power = .......................................... W [3]

(b) The signal received by the satellite is amplified and transmitted back to Earth.

(i) Suggest a frequency for the signal that is sent back to Earth.

frequency = ...................................... GHz [1]

(ii) Give a reason for your answer in (i).

..................................................................................................................................

.............................................................................................................................. [1]

Page 19: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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22

9702/41/O/N/10© UCLES 2010

ForExaminer’s

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11 (a) Wire pairs provide one means of communication but they are subject to high levels of noise and attenuation.

Explain what is meant by

(i) noise,

..................................................................................................................................

.............................................................................................................................. [1]

(ii) attenuation.

..................................................................................................................................

.............................................................................................................................. [1]

(b) A microphone is connected to a receiver using a wire pair, as shown in Fig. 11.1.

receiver

wire pair

microphone

Fig. 11.1

The wire pair has an attenuation per unit length of 12 dB km–1. The noise power in the wire pair is 3.4 × 10–9 W.

The microphone produces a signal power of 2.9 lW.

(i) Calculate the maximum length of the wire pair so that the minimum signal-to-noise ratio is 24 dB.

length = ............................................ m [4]

(ii) Communication over distances greater than that calculated in (i) is required. Suggest how the circuit of Fig. 11.1 may be modified so that the minimum

signal-to-noise ratio at the receiver is not reduced.

..................................................................................................................................

..................................................................................................................................

.............................................................................................................................. [2]

Page 20: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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9702/41/O/N/10© UCLES 2010 [Turn over

ForExaminer’s

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12 (a) Outline the principles of the use of a geostationary satellite for communication on Earth.

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...................................................................................................................................... [4]

Question 12 continues on the next page.

Page 21: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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9702/41/O/N/10© UCLES 2010

ForExaminer’s

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Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.

University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

(b) Polar-orbiting satellites are also used for communication on Earth. State and explain one advantage and one disadvantage of polar-orbiting satellites as

compared with geostationary satellites.

advantage: ......................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

disadvantage: ..................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

.......................................................................................................................................... [4]

Page 22: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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9702/43/O/N/10© UCLES 2010

ForExaminer’s

Use

12 (a) Data may be transmitted as an analogue signal or as a digital signal.

(i) Explain what is meant by

1. an analogue signal,

..................................................................................................................................

..................................................................................................................................

..................................................................................................................................

2. a digital signal.

..................................................................................................................................

..................................................................................................................................

.................................................................................................................................. [3] (ii) State two advantages of the transmission of data in digital form.

1. ...............................................................................................................................

..................................................................................................................................

2. ...............................................................................................................................

.................................................................................................................................. [2]

(b) The block diagram of Fig. 12.1 represents a system for the digital transmission of analogue data.

analoguesignal

ADCmulti-channel cable

DAC output

Fig. 12.1

(i) Describe the function of the ADC (analogue-to-digital converter).

..................................................................................................................................

..................................................................................................................................

.............................................................................................................................. [2]

(ii) Suggest why the transmission cable has a number of channels.

..................................................................................................................................

............................................................................................................................. [1]

Page 23: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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22

© UCLES 2011 9702/41/M/J/11

ForExaminer’s

Use

11 (a) Describe what is meant by frequency modulation (FM ).

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [2]

(b) A sinusoidal carrier wave has a frequency of 600 kHz and an amplitude of 5.0 V. The carrier wave is frequency modulated by a sinusoidal wave of frequency 7.0 kHz and

amplitude 2.0 V. The frequency deviation of the carrier wave is 20 kHz V–1.

Determine, for the modulated carrier wave,

(i) the amplitude,

amplitude = .............................................. V [1]

(ii) the maximum frequency,

maximum frequency = ............................................ Hz [1]

(iii) the minimum frequency,

minimum frequency = ............................................ Hz [1]

(iv) the number of times per second that the frequency changes from maximum to minimum and then back to maximum.

number = ................................................... [1]

Page 24: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

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© UCLES 2011 9702/41/M/J/11

ForExaminer’s

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12 Many television receivers are connected to an aerial using a coaxial cable. Such a cable is illustrated in Fig. 12.1.

plasticcovering

copperbraid

polytheneinsulator

copperwire

Fig. 12.1

(a) State two functions of the copper braid.

1. ......................................................................................................................................

..........................................................................................................................................

2. ......................................................................................................................................

.......................................................................................................................................... [2]

(b) Suggest two reasons why a coaxial cable is used, rather than a wire pair, to connect the aerial to the receiver.

1. ......................................................................................................................................

..........................................................................................................................................

2. ......................................................................................................................................

.......................................................................................................................................... [2]

(c) A coaxial cable has an attenuation per unit length of 200 dB km–1. The length of the co-axial cable between an aerial and the receiver is 12 m. Calculate the ratio

input signal power to coaxial cable

output signal power from coaxial cable .

ratio = ................................................... [3]

Page 25: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

Compiled and re

arranged by Sajit

Chandra Shakya

23

9702/42/M/J/11© UCLES 2011 [Turn over

ForExaminer’s

Use

11 The use of ionospheric reflection of radio waves for long-distance communication has, to a great extent, been replaced by satellite communication.

(a) State and explain two reasons why this change has occurred.

1. ......................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

2. ......................................................................................................................................

..........................................................................................................................................

.......................................................................................................................................... [4]

(b) The radio link between a geostationary satellite and Earth may be attenuated by as much as 190 dB.

Suggest why, as a result of this attenuation, the uplink and downlink frequencies must be different.

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

.................................................................................................................................... [2]

Page 26: Fig. 10.1 Chandra Sajit by rearranged · (a) On the axes of Fig. 10.2, sketch a graph to show the variation with time t of this final analogue signal. 0 0.2 18 16 signal 14 12 10

Compiled and re

arranged by Sajit

Chandra Shakya

24

9702/42/M/J/11© UCLES 2011

ForExaminer’s

Use

Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.

University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

12 (a) The signal-to-noise ratio in an optic fibre must not fall below 24 dB. The average noise power in the fibre is 5.6 × 10–19 W.

(i) Calculate the minimum effective signal power in the optic fibre.

power = ........................................... W [3]

(ii) The fibre has an attenuation per unit length of 1.9 dB km–1. Calculate the maximum uninterrupted length of fibre for an input signal of power

3.5 mW.

length = ......................................... km [3]

(b) Suggest why infra-red radiation, rather than ultraviolet radiation, is used for long-distance communication using optic fibres.

..........................................................................................................................................

.................................................................................................................................... [1]


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