Modulation What is modulation? What is modulation? a process of changing one or more properties of...

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Modulation Modulation What is modulation? What is modulation? a process of changing one or more a process of changing one or more properties of the analog carrier in properties of the analog carrier in proportion to the information signal. proportion to the information signal. One of the characteristics of the One of the characteristics of the carrier signal is changed according carrier signal is changed according to the variations of the modulating to the variations of the modulating signal. signal. AM – amplitude, AM – amplitude, E E FM – frequency , FM – frequency , ω ω PM - phase , PM - phase , θ θ

Transcript of Modulation What is modulation? What is modulation? a process of changing one or more properties of...

Page 1: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

ModulationModulation

What is modulation?What is modulation? a process of changing one or more a process of changing one or more

properties of the analog carrier in properties of the analog carrier in proportion to the information signal.proportion to the information signal.

One of the characteristics of the carrier One of the characteristics of the carrier signal is changed according to the signal is changed according to the variations of the modulating signal.variations of the modulating signal. AM – amplitude, AM – amplitude, EE FM – frequency , FM – frequency , ωω PM - phase , PM - phase , θθ

Page 2: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Modulation (cont’d)Modulation (cont’d)

Why modulation is needed?Why modulation is needed? To generate a modulated signal suited To generate a modulated signal suited

and compatible to the characteristics of and compatible to the characteristics of the transmission channel.the transmission channel.

For ease radiation and reduction of For ease radiation and reduction of antenna sizeantenna size

Reduction of noise and interferenceReduction of noise and interference Channel assignmentChannel assignment Increase transmission speedIncrease transmission speed

Page 3: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Noise, interference and Noise, interference and distortiondistortion

NoiseNoise unwanted signals that coincide with the desired unwanted signals that coincide with the desired

signals. signals. Two type of noise:internal and external noise.Two type of noise:internal and external noise.

Internal noiseInternal noise Caused by internal devices/components in the Caused by internal devices/components in the

circuits.circuits. External noiseExternal noise

noise that is generated outside the circuit. noise that is generated outside the circuit. E.g. atmospheric noise,solar noise, cosmic noise, E.g. atmospheric noise,solar noise, cosmic noise,

man made noise.man made noise.

Page 4: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Noise, interference and Noise, interference and distortion (Cont’d)distortion (Cont’d)

InterferenceInterference Contamination by extraneous signals Contamination by extraneous signals

from human sources.from human sources. E.g. from other transmitters, power lines E.g. from other transmitters, power lines

and machineries.and machineries. Occurs most often in radio systems Occurs most often in radio systems

whose receiving antennas usually whose receiving antennas usually intercept several signals at the same intercept several signals at the same timetime

One type of noise.One type of noise.

Page 5: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Noise, interference and Noise, interference and distortion (Cont’d)distortion (Cont’d)

DistortionDistortion Signals or waves perturbation caused Signals or waves perturbation caused

by imperfect response of the system to by imperfect response of the system to the desired signal itself.the desired signal itself.

May be corrected or reduced with the May be corrected or reduced with the help of equalizers.help of equalizers.

Page 6: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Limitations in Limitations in communication systemcommunication system

A) Technological problemsA) Technological problems Includes equipment availability, Includes equipment availability,

economic factors, federal regulations economic factors, federal regulations and interaction with existing systems.and interaction with existing systems.

Problem solved in theory but perfect Problem solved in theory but perfect solutions may not be practical.solutions may not be practical.

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Limitations in Limitations in communication system communication system

(cont’d)(cont’d)B) Physicals limitationsB) Physicals limitations

i) Bandwidth limitationi) Bandwidth limitation Measure of speedMeasure of speed The system ability to follow signal variations The system ability to follow signal variations

depends on the transmission bandwidth.depends on the transmission bandwidth. Available bandwidth determines the Available bandwidth determines the

maximum signal speed.maximum signal speed.

Page 8: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Limitations in Limitations in communication system communication system

(cont’d)(cont’d)ii) Noise limitationii) Noise limitation

Unavoidable.Unavoidable. The kinetic theory.The kinetic theory. Noise relative to an information signal is Noise relative to an information signal is

measured in terms of signal to noise ratio measured in terms of signal to noise ratio (SNR).(SNR).

Page 9: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Communication system Communication system designdesign

Compromise within:Compromise within: Transmission time and powerTransmission time and power SNR performanceSNR performance Cost of equipmentsCost of equipments Channel capacityChannel capacity BandwidthBandwidth

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FREQUENCY AND FREQUENCY AND WAVELENGTHWAVELENGTH

CycleCycle - One complete occurrence of - One complete occurrence of a repeating wave (periodic signal) a repeating wave (periodic signal) such as one positive and one such as one positive and one negative alternation of a sine wave.negative alternation of a sine wave.

FrequencyFrequency - the number of cycles of - the number of cycles of a signal that occur in one second.a signal that occur in one second.

PeriodPeriod - the time distance between - the time distance between two similar points on a periodic two similar points on a periodic wave.wave.

WavelengthWavelength - the distance traveled - the distance traveled by an electromagnetic (radio) wave by an electromagnetic (radio) wave during one period.during one period.

W2-2

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One cycle

time

PERIOD AND FREQUENCY COMPARED

Frequency = f = 1/T

T = One period

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+

0 time

distance

Frequency and wavelength compared

f = 1/T

T

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CALCULATING WAVELENGTHCALCULATING WAVELENGTHAND FREQUENCYAND FREQUENCY

= wavelength in metersf = frequency in MHz

= 300/f

f = 300/

C = f where C = 3 x 108 m/s (speed of light)

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ELF

103 m

107 m

104 m

105 m

106 m

10 m

1 m

10-1 m

10-2 m

10-3 m

10-4 m

102 m

300

Hz

30 H

z

30 k

Hz

3 k

Hz

300

kH

z

30 M

Hz

3 M

Hz

300

MH

z

3 G

Hz

300

GH

z

30 G

Hz

THE ELECTROMAGNETIC SPECTRUM FROM 30 HZ TO 300 GHZ

UHFVHFHFMFLFVLFVF SHF EHF

Frequency

Wavelength

Mill

imet

erw

aves

( = 300/f)

(f = 300/)

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LOW AND MEDIUM LOW AND MEDIUM FREQUENCIESFREQUENCIES

Extremely Low FrequenciesExtremely Low Frequencies - 30 to 300 Hz - 30 to 300 Hz

Voice FrequenciesVoice Frequencies - 300 to 3000 Hz - 300 to 3000 Hz

Very Low FrequenciesVery Low Frequencies - 3 kHz to 30 kHz - 3 kHz to 30 kHz

Low FrequenciesLow Frequencies - 30 kHz to 300 kHz - 30 kHz to 300 kHz

Medium FrequenciesMedium Frequencies - 300 kHz to 3 MHz - 300 kHz to 3 MHz

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HIGH FREQUENCIESHIGH FREQUENCIES High FrequenciesHigh Frequencies - 3 MHz to 30 MHz - 3 MHz to 30 MHz

Very High FrequenciesVery High Frequencies - 30 MHz to 300 MHz - 30 MHz to 300 MHz

Ultra High FrequenciesUltra High Frequencies - 300 MHz to 3 GHz - 300 MHz to 3 GHz (1 GHz and above = microwaves)(1 GHz and above = microwaves)

Super High FrequenciesSuper High Frequencies - 3 GHz to 30 GHz - 3 GHz to 30 GHz

Extremely High Frequencies Extremely High Frequencies - 30 GHz to 300 - 30 GHz to 300 GHzGHz

Page 17: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Band name Abbr ITU band

Frequency and Wavelength

Example uses

< 3 Hz > 100,000 km

Extremely low frequency

ELF 1 3–30 Hz 100,000 km – 10,000 km

Communication with submarines

Super low frequency

SLF 2 30–300 Hz 10,000 km – 1000 km

Communication with submarines

Ultra low frequency

ULF 3 300–3000 Hz 1000 km – 100 km

Communication within mines

Very low frequency

VLF 4 3–30 kHz 100 km – 10 km

Submarine communication, avalanche beacons, wireless heart rate monitors, geophysics

Low frequency LF 5 30–300 kHz 10 km – 1 km

Navigation, time signals, AM longwave broadcasting

Medium frequency

MF 6 300–3000 kHz 1 km – 100 m

AM (Medium-wave) broadcasts

High frequency HF 7 3–30 MHz 100 m – 10 m

Shortwave broadcasts, amateur radio and over-the-horizon aviation communications

Very high frequency

VHF 8 30–300 MHz 10 m – 1 m

FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications

Ultra high frequency

UHF 9 300–3000 MHz 1 m – 100 mm

television broadcasts, microwave ovens, mobile phones, wireless LAN, Bluetooth, GPS and Two-Way Radios such as FRS and GMRS Radios

Super high frequency

SHF 10 3–30 GHz 100 mm – 10 mm

microwave devices, wireless LAN, most modern Radars

Extremely high frequency

EHF 11 30–300 GHz 10 mm – 1 mm

Radio astronomy, high-speed microwave radio relay

Above 300 GHz < 1 mm

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Longwave AM Radio = 148.5 - 283.5 kHz Longwave AM Radio = 148.5 - 283.5 kHz (LF) (LF)

Mediumwave AM Radio = 535kHz - Mediumwave AM Radio = 535kHz - 1605kHz (MF) 1605kHz (MF)

TV Band I (Channels 2 - 6) = 54MHz - TV Band I (Channels 2 - 6) = 54MHz - 88MHz (VHF) 88MHz (VHF)

FM Radio Band II = 88MHz - 108MHz (VHF) FM Radio Band II = 88MHz - 108MHz (VHF) TV Band III (Channels 7 - 13) = 174MHz - TV Band III (Channels 7 - 13) = 174MHz -

216MHz (VHF) 216MHz (VHF) TV Bands IV & V (Channels 14 - 69) = TV Bands IV & V (Channels 14 - 69) =

470MHz - 806MHz (UHF) 470MHz - 806MHz (UHF)

Public Broadcast Frequencies

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FCC Channel Bandwidth FCC Channel Bandwidth AllocationsAllocations

FCC : Federal Communications Commission, United States

AM broadcast 535 kHz – 1605 kHz 106 10kHz

Citizen band 26.965 MHz – 27.405 MHz 40 10kHz

FM broadcast 88 MHz – 108 MHz 100 200kHz

TV broadcast 54 MHz – 806 MHz 67 6MHz

Designation Frequency Range No. of Channels Bandwidth

Page 20: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

10-3 m

10-4 m

300

GH

zM

illi

met

erw

aves

THE ELECTROMAGNETIC SPECTRUM ABOVE 300 GHZ

Wavelength

0.8

x 10

-6 m

0.4

x 10

-6 m

Infr

ared

Vis

ible

Ult

ravi

olet

X-r

ays

Gam

ma

rays

Cos

mic

ray

s

10-5 m

Page 21: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

OPTICAL FREQUENCIESOPTICAL FREQUENCIES

InfraredInfrared - 0.7 to 10 micron - 0.7 to 10 micron

Visible lightVisible light - 0.4 to 0.8 micron - 0.4 to 0.8 micron

UltravioletUltraviolet - Shorter than 0.4 - Shorter than 0.4 micronmicron

Note: A micron is one millionth of a meter. Light waves are measured and expressed in wavelength rather than frequency.

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TYPES OF TYPES OF COMMUNICATIONSCOMMUNICATIONS

TX RX

TX

TX

RX

RX

Simplex:One-way

Duplex:Two-wayHalf duplex:Alternate TX/RXFull duplex:SimultaneousTX/RX

Channel

Channel(s)

Page 23: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

COMMUNICATIONS COMMUNICATIONS SIGNAL VARIATIONSSIGNAL VARIATIONS

BasebandBaseband - The original - The original information signal such as audio, information signal such as audio, video, or computer data. Can be video, or computer data. Can be analog or digital.analog or digital.

BroadbandBroadband - The baseband signal - The baseband signal modulates or modifies a carrier modulates or modifies a carrier signal, which is usually a sine signal, which is usually a sine wave at a frequency much higher wave at a frequency much higher than the baseband signal.than the baseband signal.

Page 24: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Frequency Spectrum Frequency Spectrum &Bandwidth&Bandwidth

The frequency spectrum of a waveform The frequency spectrum of a waveform consists of all frequencies contained in consists of all frequencies contained in the waveform and their amplitudes the waveform and their amplitudes plotted in the frequency domain.plotted in the frequency domain.

The bandwidth of a frequency The bandwidth of a frequency spectrum is the range of frequencies spectrum is the range of frequencies contained in the spectrum. It is contained in the spectrum. It is calculated by subtracting the lowest calculated by subtracting the lowest frequency from the highest. frequency from the highest.

Page 25: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Frequency Spectrum Frequency Spectrum &Bandwidth&Bandwidth

(cont’d)(cont’d) Bandwidth of the information signal Bandwidth of the information signal

equals to the difference between the equals to the difference between the highest and lowest frequency highest and lowest frequency contained in the signal.contained in the signal.

Similarly, bandwidth of Similarly, bandwidth of communication channel is the communication channel is the difference between the highest and difference between the highest and lowest frequency that the channel lowest frequency that the channel allow to pass through itallow to pass through it

Page 26: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Gain and Loss

Electronic System

Pin

Vin

Iin

Pout

Vout

Iout

If ratio Pout /Pin > 1 , power gain.If ratio Pout /Pin < 1 , power loss.

If ratio Vout /Vin > 1 , voltage gain.If ratio Vout /Vin < 1 , voltage loss.

If ratio Iout /Iin > 1 , current gain.If ratio Iout /Iin < 1 , current loss.

W2-3

Page 27: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Signal GainSignal Gain

Voltage amplifier: Voltage amplifier: AAvv= V= Voo/V/Vii..

Transistors current gain: Transistors current gain: = i = icc/i/ib,b,

Step-up voltage transformer, VStep-up voltage transformer, Vsecondary secondary > > VVprimaryprimary

Step-up current transformer, IStep-up current transformer, Isecondary secondary > > IIprimaryprimary

In some cases, signal gain may be >1 In some cases, signal gain may be >1 eventhough the power gain is < 1.eventhough the power gain is < 1.

Occasionally, a signal loss or power loss is also called as signal attenuation or power attenuation.

Page 28: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Power GainPower Gain It is the ratio of output power over input It is the ratio of output power over input

power. power.

AApp = P = Poo/P/Pii..

In amplifiers, the power gain may be In amplifiers, the power gain may be more than one. The signal power is more than one. The signal power is amplified. DC power supply is amplified. DC power supply is transformed into signal power.transformed into signal power.

Page 29: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Power and voltage gains in Power and voltage gains in communicationcommunication

The term decibels (dB) is a relative unit of The term decibels (dB) is a relative unit of measurementmeasurement

used frequently in electronic communication to used frequently in electronic communication to describedescribe

gain or loss.gain or loss.

Power gain in dB = 10 log (PPower gain in dB = 10 log (Poo/P/Pii) )

Voltage gain in dB = 20 log (VVoltage gain in dB = 20 log (Voo/V/Vii))

Page 30: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Power ratio PPower ratio Poo/P/Pii = 10,000 = 40 dB = 10,000 = 40 dB

Voltage ratio VVoltage ratio Voo/V/Vii = 100 = 40 dB. = 100 = 40 dB.

See that PSee that Poo/P/Pi i = (V= (Voo/V/Vii))22

hence, (Phence, (Poo/P/Pii)) dB dB = 2(V= 2(Voo/V/Vii))dBdB

Page 31: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Alternatively:Alternatively:

Power gain ratio Power gain ratio = 10= 10 (gain in dB/10)(gain in dB/10)

Voltage gain ratio = 10 Voltage gain ratio = 10 (gain in dB/20)(gain in dB/20)

Example 1:Example 1:

Convert a power gain of 64 dB into ratio.Convert a power gain of 64 dB into ratio.

64 dB = 1064 dB = 10(64/10)(64/10) = 10 = 10(6.4) (6.4) =2.5212 x 10=2.5212 x 1066

Page 32: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

In this case, PIn this case, Poutout= 0.01 P= 0.01 Pinin

Therefore, Power gain (dB)Therefore, Power gain (dB)= 10 = 10 log(0.01)log(0.01)

= = -20 dB-20 dB

When the answer is When the answer is negativenegative, indicates a loss , indicates a loss oror

attenuation.attenuation.

Example 2 :What is the dB gain or loss for a certain system when thePower out of a certain system is 0.01 times the power in?

Page 33: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Example 3:Example 3:

Let there be two amplifiers in Let there be two amplifiers in cascade as shown. Their gains are cascade as shown. Their gains are 13 dB and 10 dB respectively. 13 dB and 10 dB respectively.

The overall gain at the output is 13+10 = The overall gain at the output is 13+10 = 23 dB.23 dB.

A1 A2

13dB gain 10dB gain

Output

Page 34: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

In terms of ratio:In terms of ratio:

23 dB = 1023 dB = 10(23/10)(23/10)= 200= 200

13 dB = 1013 dB = 10(13/10)(13/10)= 20= 20

10 dB = 1010 dB = 10(10/10)(10/10)= 10= 10

Again 20 x 10 = 200.Again 20 x 10 = 200.

Page 35: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Relative dBRelative dB It is convenient to express signals with It is convenient to express signals with

some reference such as some reference such as 1mW power or, 1mW power or, 1 1 V voltage level.V voltage level.

This permits input- and output- signals to This permits input- and output- signals to be expressed in terms of relative dB.be expressed in terms of relative dB.

When referenced to 1mW, it is written dBmWhen referenced to 1mW, it is written dBm When referenced to 1 When referenced to 1 V, it is written as V, it is written as

dBdBVV When referenced to 1W, it is written dBWWhen referenced to 1W, it is written dBW When referenced to 1 V, it is written as When referenced to 1 V, it is written as

dBVdBV

Page 36: Modulation What is modulation? What is modulation?  a process of changing one or more properties of the analog carrier in proportion to the information.

Relative dBRelative dB isis not an absolute gain but not an absolute gain but is termed as gain with respect to a is termed as gain with respect to a reference unit.reference unit. Examples :Examples :

a) For a 5 watts signal in reference to 1mW,a) For a 5 watts signal in reference to 1mW,

the relative dB; 10 log(5W/1mW) = 36.99 the relative dB; 10 log(5W/1mW) = 36.99 dBmdBm

b) For a 500 b) For a 500 V signal in reference to a 1 V signal in reference to a 1 V ,V ,

the relative dB; 20 log(500 the relative dB; 20 log(500 V /1 V /1 V ) = V ) = 53.98dB53.98dB V V