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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
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
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.
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.
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.
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.
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.
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).
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
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
One cycle
time
PERIOD AND FREQUENCY COMPARED
Frequency = f = 1/T
T = One period
+
0 time
distance
Frequency and wavelength compared
f = 1/T
T
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)
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/)
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
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
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
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
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
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
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.
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)
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.
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.
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
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
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.
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.
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))
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
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
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?
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
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.
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
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