COMMUNICATION SYSTEM- its primary purpose is to transfer information from one place to another

> TRANSMISSION, RECEPTION & PROCESSING of INFORMATION between twoor more locations using electronic circuits

BLOCK DIAGRAM:

TRANSMITTER - is a collection of one or more electronic devices or more electronicdevices or circuits that converts the original source information to a form more suitablefor transmission over a particular transmission medium

TRANSMISSION MEDIUM - provide a means of transporting signals between atransmitter and receiver

RECEIVER - is a collection of electronic devices and circuits that accepts thetransmitted signals from the transmission medium and then converts those signals back totheir original form

SYSTEM NOISE - is any unwanted electrical signals that interfere with the informationsignal

TRANSMITTERTRANSMISSION MEDIUM

orCOMMUNICATION CHANNEL

RECEIVER

NOISE

TYPES OF ELECTRONICS COMMUNICATIONS

1. One - way or two way transmissions2. Analog versus digital signals3. Baseband or modulated signals

1. Classification of Communication Systems

A.) SIMPLEX , SX- communication travels in one direction only- receive-only , transmit only , one way only

E.g. Radio & TV broadcasting , telemetry

WIRE WIRELESS

B.) HALF DUFLEX , HDX- two way communication but the direction alternates- two way alternative , either way line

E.G. Radio communication in military,fire, police , fax machine , intercom

A B A B

A B A B

A B A B

C.) FULL DUPLEX , FDX- can send and receive simultaneously- two -way simultaneous , both way lines

E. G.

D.)FULL/ FULL DUPLEX , F/FDX- transmission of signals of many points

E.G. Networking, multipoint cellphone

2. Types of intelligence

A.) ANALOG SIGNAL- continuously varying voltage or current

B.) DIGITAL SIGNAL- earliest forms of both wire and radio communication uses on/off digital code

A B A B

3. BASEBAND TRANSMISSION- putting the original voice , video or digital signals directly into the medium

Info can be transmitted by themselves over the medium or may be used to modulate acarrier

Eg.

Telephone and Intercom communication system Voice place on wires and transmitted same distance to the receiver Computer networks - digital signals are applied directly to coaxial cable for

transmission to another computer

BUT........ Incompatibility problems.........

BASIC PRINCIPLES

BASIC PRINCIPLESAND CONCEPTS:

1. FREQUENCY (f)- the number of times a particular phenomenon occurs in a givenperiod of time

- may be a number of voltage polarity alternations or electromagneticfield oscillations that takes place in a span of time

- measured in cycle per second(cps) or Hertz(Hz)* CYCLE - each alternation or oscillation

2. WAVELENGTH( ) - is the distance between two points of similar cycles of aperiodic wave- distance traveled by an electromagnetic wave during the time ofone cycle

fC

3. BANDWIDTH(BW) - is the range of frequencies over which the operation of asystem is guaranteed satisfactory

- it is a portion of the electromagnetic spectrum occupied by acertain signal

QBW

fff r12

Where: f2 = upper cut-off frequencyf1 = lower cut-off frequencyfr = resonant frequencyQ = quality factor

4. POWER (P) and DECIBELS (dB)

POWER - its the fundamental quantity representing the rate at which energy is used- readily measurable since it can be converted to heat

DECIBEL - literally means one-tenth of a bel

“Everything here on earth is analog in nature”

CHARACTERSITIC of A SINEWAVE

1. AMPLITUDE - how high or low the signal varies- called in sound energy as the LOUDNESS and SOFTNESS

PERFECT SINE WAVE - same peak to peak- symmetrical

2. FREQUENCY - is the number of and per second- numbers of repetition- low and high

Alto - lowest female vocal voiceBass - lowest male voiceTenor - higest male voiceSoprano - highest singing voice

3. PHASE - phase angle of the signal

in phase Out of phse

ELECTROMAGNETIC SPECTRUM

WAVES - form of energy that travels from one vibrating particle to the next vibratingparticle of the medium

EMW - form of energy that travels in free space with the speed of light Antenna - most important for communication system

- it depends on the physical length or electrical length

RADIO-FREQUENCYWAVE PROPAGATION

“ once a radio signal has been radiated by the antenna , it will travel or propagatethrough space and ultimately reach the receiving antenna”

FACTORS:

Frequency of the signal Atmospheric conditions Time of the day

3 BASIC PATH

1. ) GROUND Leaves the antenna and remains close to the earth Will follow the curvature of the earth Strongest at low and medium frequency Amplitude modulation , broadcast signals At frequency beyond 3 MHz earth begins to attenuate with in several miles of

the antenna

2. ) SKYWAVE SIGNALS Radiated by the antenna into the uper atmosphere where it is bent or reflected back to

earth

3. ) DIRECT or SPACEWAVES Travels in a straight line directly from the transmitting antenna to the receiving

antenna LINE-OF-SIGHT COMMUNICATIONS not refracted nor follow the curvature of the earth block due to the curvature of the earth Antenna must be high enough Limited to short distances and height of antennas Radio above 30 MHz FM and TV broadcast are limited Antennas on top of the building for good reception

PURPOSE OF COMMUNICATION SYSTEM

Is to communicate information between two or more locations Accomplished by converting the original info into electromagnetic energy and

transmitting to one or more stations and coverted back to original form

EM energy can propagate as a voltage or current along metallic wires , emitted radiowaves through space , or as light waves down to an optical fiber

is distributed throughout an almost infinite range of frequencies are signals that oscillate Field intensities fluctuate up and down a given number of times/second The oscillations may occur at a very low or at an extremely high frequency

RADIO FREQUENCY SPECTRUM

BAND NUMBER FREQUENCY DESIGNATIONS12345678910111213141516171819

ELECTROMAGNETIC SPECTRUM

1. EXTREMELY LOW FREQUENCIES (ELF’s)> 30 - 300 Hz> Power line frequencies (50 and 60 Hz) and low end human hearing range

2. VOICE FREQUENCIES(VFs)> 300 - 3000 Hz> normal rang of human speech> hearing ( 20-20,000 Hz)

3. VERY LOW FREQUENCIES (VLFs)> higher end of the human range (15 - 20 KHz)> musical instruments> government and military communications

4. LOW FREQUENCIES (LFs)> 30 300 kHz> used in aeronautical and marine navigation> used in subcarriers

5. MEDIUM FREQUENCIES (MFs)> 300 - 3000 kHz> AM broadcasting (535 - 1605 kHz)> marine and aeronautical communication applications

6. HIGH FREQUENCIES (HFs)> generally know as the short waves> all kinds of two-way radio communications and shortwave radio broadcasting> government and military services> amateur radio and CB communications

7. VERYHIGH FREQUENCIES (VHFs)> 30 - 300 MHz range> used by many services ( mobile radio, marine and aeronautical communications)> FM radio broadcasting (88 - 108 MHz)> TV channels 2-13> radio amateurs

8. ULTRAHIGH FREQUENCIES (UHFs)> 300 - 3000 MHz> extremely widely used portion> UHF TV channels 14- 83> widely used for land mobile communications and services> military services> radar and navigational services> microwaves ( above 1000-MHz) 1GHz

9. SUPERHIGH FREQUENCIES (SHFs)> 3 - 30 GHz> microwave frequencies used in satellite communications and radar> specialized two-way radio communications

10. EXTREMELYHIGH FREQUENCIES ( EHFs)> 30 - 300 GHz>equipment in this range is extremely complex and expensive> signals above this range are referred as millimeter waves> satellite communications and specialized radar

RADIO µWAVE INFRARED VISIBLE ULTAVIOLET X-RAY GAMMARAY

INFRARED - sandwiched between the highest frequency and visible portion-often given in microns

1 micron = i millionth of a meter

- two areas the long and the short infrared

A. Long infrared 0.01mm-1000nmB. Short infrared 1000-700 nm

- refers to the radiation that is generally associated with heat

Light bulbs , our bodies , physical equipment that generates heat

USES:1. Astronomy2. Guidance in weapons systems3. TV remote controls

-uses optical devices to process and manipulate signals

VISIBLE SPECTRUM- above the infrared region and as referred to LIGHT- express in angstroms

1 Ǻ = 1 ten thousandth of a micron

- 800 Å (red) - 400 Å (violet)- can be modulated and transmitted thru glass fibers

*Fiber optics - fastest growing specialties of communications electronics- high frequency to handle tremendous amount of information

-can be transmitted through free space

* Laser - can easily be modulated with voice,video and data information

POWERAND DECIBEL

- fundamental quantity representing the RATE at which ENERGY is used- readily measurable since it can be converted to HEAT- indicates relation between two powers- ratio that indicates the relationship between 3 parameters

DECIBEL COMPUTATION

dBW =dBm =dBu =dBn =

dBmdBmdBmdBmdBdBudBdBndBdBm

DECIBEL - logarithmic unit

E.g. it measures magnitude of earthquake

Richter scale -measures intensity of an earthquake relative to a reference intensity

- measures the acoustical signals dB - SPL

0 dB - SPL - threshold of hearing120 dB - SPL - threshold of pain120 - 140 - engine

Electronic communication - power ratios are enormous range , excessively large orextremely small numbers

1/6.) Convert the absolute value power ratio of 200 to a power gain in dB

2/6.) Convert a power gain Ap = 23 dB to an absolute power ratio

3/7.) Convert a power level of 200 mW to dBm

1 NEPER = 8.686 dB

20 / ln 10 = 8.686

GTx = 3 dBmPo = 4 dBPo = 4 dBm

SEATWORK and HOMEWORK:

1/8.) Convert a power of 23 dBm to an absolute power

2. A communication cable is installed and the signal level in volts increased by 1/2 or50% . What is the increased in dB?

3. A signal is amplified 100 times in power , the dB gain is

4. A signal is attenuated from 5V - 0.1 V?

2/8.) A three stage system comprised of two amplifiers and one filter . The input powerPin = 0.1 mW . Absolute power gains are Ap1 = 100 , Ap2 = 40 , Ap3 = 0.25

DetermineA. Input power in dBmB. Output power in watts and dBmC. dB gain of each three stagesD. Overall gain

BANDWIDTHAND INFORMATION CAPACITY

1. All practical communication channel - BANDLIMITED It pass frequency from dc to some upper limit It has both lower and upper cut-off frequencies

2. All channel are noisy

General rule: Communication channel propagate a signal that contains a frequency thatis changing at a rate greater than the bandwidth of the channel

Information theory - is highly a theoretical study of the efficient use of bandwidth topropagate information through electronic communications systems

- can be used to determine the information capacity of a data communicationsystem

Information capacity - is a measure of how much information can be propagated througha communications system and is a function of bandwidth and a transmissiontime

Binary digit or bit - most basic digital symbol used to represent an information

Bit rate - the number of bits transmitted during 1 s and is expressed in bits per second(bps)

HARTLEY’s LAW

tBI

Where: I = information capacity (bits per second)B = bandwidth (hertz)T = transmission time (seconds)

kTBI I = amount of information to be sentk = constantT = time availableB = channel bandwidth

MAXIMUM THEORITICALDATARATE

SHANNON-HARTLEYTHEOREM

MBC log2 2

Where:C = information capacity , bits/sB = channel bandwidth , HzM = number of levels transmitted

- for a given noise level a maximum data rate cannot be exceeded without errors

Binary InformationC= 2B

SHANNON limit for information capacity

NSI

NSI

B

B

1

1

log32.3

log

10

2

Where: I = information capacity (bps)B = bandwidth (hertz)

NS = signal-to-noise power ratio (unitless)

= as power ratio not in decibel

Homework:1-9/21) For a standard telephone circuit with a signal-to-noise power ratio of

1000 (30 dB) and a bandwidth of 2.7 kHz, determine the Shannon limitinformation capacity

2.) A telephone line has a bandwidth of 3.2 kHz and a signal-to-noise ratio of 35dB. A signal is transmitted down this line using a four-level code. What is themaximum theoretical data rate.

ELECTRICALNOISE

> as any undesirable electrical energy that falls within the passband of the signal> random and unpredictable electrical signals produced by natural processes both internaland external to the system

* message may be partially corrupted or totally obliterated

Classification:1. Correlated2. Uncorrelated

* Uncorrelated Noise - is present regardless of whether there is a signal present or not

A. External noiseB. Internal noiseC. Man-made noise

A. External noise - noise that is generated outside the device or circuit

Primary Sources:

1. Atmospheric noise - also called Static electricity- naturally occurring electrical disturbances that originate

within Earth’s atmosphere- caused by LIGHTNING discharges in thunderstorms- sputtering ,crackling- form of impulses that spread energy throughout a wide range

of frequencies- relatively insignificant at frequencies above 30 MHz

2. Extraterrestrial noise - consist of electrical signals that originate from outsideEarth’s atmosphere- deep space noise-originates from the Milky way and other galaxies, and thesun

A. Solar noise - directly from the sun’s heat* quite condition - a relatively constant radiation intensity exist* high intensity or sporadic disturbances caused by sunspot activity

and solar flare-upsSolar cycle repeats every 11 years

SOLAR CYCLE - sunspot solar flares- influences weather on earth

Solar flares - magnetic energy associated with sunspots Sun’s spots - magnetic storm on the surface of the Sun

ITAFFECTS

Damage 21st satellites and other hi-tech systems Radiation hazards for astronauts and satellites caused by quite sun Weather on Earth

CO2 level volcanic eruptions Sun’s activity El Nino Global climate change

Solar flares 2014

B. Cosmic noise - continuously distributed throughout galaxies- black body noise

what they lack in nearness, they nearly makeup in numbers

- RF noise radiated by DISTANT STARS

3. Man- made noise - noise that is produced by mankind- most intense in a more densely populated metropolitan andindustrial areas- INDUSTRIAL NOISE

Spark-producing mechanism Commutators in electric motors Auto mobile ignition systems Ac power generating Switching equipment Fluorescent lights

- impulsive in nature and contains wide range of frequencies thatare propagated through space in the same manner as radio waves

B. Internal Noise - is electrical interference generated within a device or circuit

1. Shot noise2. Partition noise3. Excess noise4. Transit time noise5. Thermal noise

Shot noise - is caused by the random arrival of carriers at the output element ofan electronic device

- randomly varying and is superimposed onto any signal present- transistor noise- first observed in the anode current of a vacuum tube amplifier

(W. Schottky)- when amplified sounds like metal pellets falling in a thin roof- additive to thermal noise

BI nn qI2

Where:q = electron charge C10602.1 19

I = direct diode current , AB n = equivalent noise bandwidth , Hz

Transit time noise - any modification to a stream of carrier as they pass from theinput to the output of the device- produces irregular, random variation and is determine bycarrier mobility, bias voltage, and transistor construction-significant @ high frequency

Thermal noise (temperature dependent)- is associated with the rapid and random movement of electrons

within a conductor due to thermal agitation- Brownian noise, Johnson noise, White noise,random noise

Brownian noise (discoverer)- first observed by Robert Brown in a particle nature of matter in pollen grain samephenomenon with the smoke particle

Johnson noise (related to Brownian particle- Kinetic Theory)- J.B. Johnson of Bell laboratory first recognize the random movement of electronsEach flight of electrons between collisions with molecules constitutes a short pulse ofcurrent and develops a small voltage

Random noise - due to its random movement at all direction- produces an AC component

White noise - analogous to the color- containing all colors or frequency of light- prism test

Other noise:

Partition noise - similar to shot noise but occurs only in dives of single currentseparate into two or more path

Excess noise ( flicker noise , 1/f noise , pink noise )- more energy at lower frequency- insignificant at 1 kHz

Thermal noise sets the upper bound on the performance of a communication system

> is the random motion of free electrons within a conductor caused by thermal agitation

NOISE POWER

N = KTB

Where: N = noise power (watts)B = bandwidth (hertz)

KJK 1038.1 23

T = absolute temperature (Kelvin)

Noise Power, dBm

001.0log10)(

KTBN dBm BdBm

BKT

N

N

dBm

dBm

log10174

log10001.0

log10

)(

)(

NOISE VOLTAGE

KTBRV n 4

Example:

For an electronic device operating at a temperature of 17°C with a bandwidth of 10 kHz,determineA. Thermal noise power in watts and in dBmB. rms noise voltage for a 100-ῼ internal resistance and a 100-ῼ load resistance

NOISE DUE TO SEVERAL SOURCES

For Series Sources:

Totaltotal KTBRVn 4

Where: RRRRR nTotal ......321

For Parallel Sources:

TotalTotal KTBRVn 4

Where:RRRRR ntotal

1........1111

321

Noise Due To Several Amplifiers in Cascade:

AAR

ARReqR 2

221

321

21

H.W. 1 whole long bondpaper,copy and answer...Organize well your solution.

1. The first stage of a two stage amplifier has a voltage gain of 10, a 600ῼ inputresistance (R1), a 1600ῼ equivalent noise resistance and 27 kῼ output resistance. For thesecond stage these values are 25, 81kῼ, 10kῼ, 1Mῼ respectively. Calculate the Req inputnoise resistance of 2 stage amplifier. Calculate the noise figure of the amplifier if it isdriven by a generator whose output impedance is 50ῼ, bandwidth of 5 kHz.Calculate theequivalent noise temperature. Calculate the total noise voltage.

Research and do study noise temperature,noise factor,noise figure

CORRELATED NOISE- is a form on int

ernal noise that is correlated to the signal and cannot be present in a

circuit unless there is a signal- “NO SIGNAL, NO NOISE”- produce by a non-linear amplification and includes harmonic and intermodulationdistortion

* nonlinear distortion - creates unwanted frequencies that interfere with the signaland degrade performance

* harmonic distortion - occurs when unwanted harmonics of a signal are producedthrough nonlinear amplification

- amplitude distortionHarmonics - integers multiples of the original signal

Example:

Determine 2nd , 3rd and 12th harmonic for a 1-kHz repetitive wave

*intermodulation distortion - is the generation of unwanted sum and differencefrequencies produced when two or more signals mix in a non-linear device

Cross products - sum and difference of frequencies- are produce when harmonics as well as fundamental frequenciesmix in a non-linear device

Cross product = nfmf 21

Where: f1 and f2 = fundamental frequenciesm and n = positive integers between 1 and ∞

ff 21

Example:

2.For a non-linear amplifier with two input frequencies, 3 kHz and8kHz,determineA.) First three harmonics present in the output for each input frequencyB.) Cross- product frequencies produced for values of m and n of 1 and 2

IMPULSE NOISE - is characterized by a high amplitude peaks of short duration in thetotal noise spectrum- consist of sudden burst of irregularly shaped pulses that are

generally last between a few microseconds and several milliseconds,depending on their amplitude and origin

Sources:1. Transients from electromechanical switches2. Electric motors3. Appliances4. Electric lights and power lines5. Automotive ignition systems6. Poor -quality solder joints and lightning

ELECTRICAL NOISE SOURCE SUMMARY:Correlated noise ( internal)

Nonlinear distortionHarmonic distortionIntermodulation distortion

Uncorrelated noiseExternal

AtmosphericExtraterrestrial

SolarCosmic

Man-madeImpulseInterference

InternalThermalShotTransient time

ELECTRICAL INTERFERENCE - occurs when information signals from one sourceproduce frequencies that fall outside their allocated bandwidth and interfere withinformation signals from another source

- contamination by extraneous signals from sources andother transmitters, power lines and machinery and switchingcircuits

-occurs most often in radio systems whose receivingantennas usually intercept general signals at the same time

RFI ( Radio Frequency Interference) -appears in cable systems

- occurs in the radio-frequency spectrum

Signal-to-Noise Power Ratio

- is the ratio of the signal power level to the noise power level

Mathematically,

PPN

S

NS

Where: Ps = signal power (watts)Pn = noise power ( watts)

> is often expressed as a logarithmic function with the decibel unit

PPN

SdBNS log10)(

Example:1. For an amplifier with an output signal power of 10 W and output noise power of

0.01 W,determine the signal-to-noise power ratio and in decibels

> can also be expressed in terms of voltages and resistances

RVR

V

out

n

in

S

dBNS

2

2

log10)(

Where: S/N = signal-to-noise power ratio (decibels)Rin = input resistance (ohms)Rout = output resistance (ohms)Vs = signal voltage ( volts)

VV

N

SdBNS log20)(

Example:

For an amplifier with an output signal voltage of 4 V an output noise voltage 0.005 V, andan input and output resistance of 50 ῼ, determine the signal-to-noise power ratio

NOISE FACTOR and NOISE FIGURE

Noise factor (F) and Noise figure (NF) - are figures of merits used to indicate how muchthe signal-to-noise ratio deteriorates as a signal passes through a circuit or series ofcircuits

Noise factor (F)- is simply a ratio of input signal-to-noise power ratio to outputsignal-to-noise power ratio

)(unitlessratiopowernoisetosignaloutputratiopowernoisetosignalinputF

Noise figure (NF) - is simply the noise factor stated in dB- a parameter used to indicate the quality of a receiver

ratiopowernoisetosignaloutputratiopowernoisetosignalinputdBNF

log10)(

FdBNF log10)(

- indicates how much the signal-to-noise ratio deteriorates as a waveformpropagates from the input to the output of a circuit

For a perfect, noiseless circuit

F = 1 NF = 0 dB

HOMEWORK:

For a nonideal amplifier and the following parameters, determineA. ) input S/N ratio (dB)B. ) output S/N ratio (dB)C. ) Noise factor and noise figure

Input signal power = W102 10

Input noise power = W102 18

Power gain = 1,000,000Internal noise (Nd) = W106 12

FRISS’ FORMULA - is used to calculate the total noise factor of several cascadedamplifiers

AAAF

AAF

AFFF

n

nT ....

111

212

3

1

21

1

Note: In Friss’ formula , the noise figure must be converted to noise factors

FNF TT dB log10)(

Example:

For three cascaded amplifier stages, each with noise figure of 3dB and a power gains of10 dB, determine the total noise figure

EQUIVALENT NOISE TEMPEARTURE (Te)

- is a hypothetical value that cannot be directly measured- a convenient parameter often used in VHF, UHF,microwave and satellite radio receivers

KBNT

where: T = environmental temperature (kelvin)N = noise power (watts)K = Boltzmann’s constant (J/K)B = bandwidth (Hz)

)1( FTT e

Where: Te = equivalent noise temperature (kelvin)T = environmental temperature ( 290 K)F = noise factor (unitless)

TT

a

eF 1

Determine

A. Noise figure for an equivalent noise temperature of 75 KB. Equivalent noise temperature for a noise figure of 6 dB

AMPLITUDE MODULATION TRANSMISSION

MODULATION - The process of impressing low-frequency information signals onto ahigh- frequency carrier signal- one of the principal technique used in electronic communication

TYPES OFMODULATION

ANALOG DIGITAL

AMPLITUDE ANGULAR DIGITAL MODULATION PULSE MODULATIONAM FM PM FSK PSK QAM PAM PWM PCM

3 PRINCIPALTYPES

Amplitude modulation Frequency modulation Phase modulation

- process of modifying the characteristics of one signal in accordance with somecharacteristics of another signal

Voice signals Video signals Binary data

“ CABLE ARE SOMETIMES IMPRACTICAL”

it is desirable to translate the information signal to a point higher in theelectromagnetic frequency spectrum

MODULATING SIGNAL- can be of any shape that permits both the analog and digital

MODULATEDWAVE- usually a sine wave- considered to be higher than the highest information frequency to be transmitted

A.) CARRIER

RF range : 20 kHz - 300 Ghz

- frequency annd amplitude are constant- no information

fEEe

cc

ccc t

2sin

sin

B. MODULATING SIGNAL

Audio frequency : 20 Hz - 220 kHz

tEm

tEm

fe

m

mm

2sin

sin

AMPLITUDE MODULATION- a system of modulation in which the amplitude of the carrier is made proportional tothe instantaneous amplitude of the modulating voltage

BASIC AM CIRCUIT

“ THRE HISTORY OF AM IS ALSO THE HSTORY OF EARLY RADIO BROADCASTINGSINCE AM WAS THE FIRST RADIO SIGNAL”

1895 - GUGLIELMO MARCONI - invented radio - telegraph code

Joseph Henry Michael Faraday James Clark Maxwell Heinrich Hertz

1 mile - 1st radio broadcast tranmission

1901 - Marconi send telegraph signals across the Atlantic

15 years - AM radio transmitted only telegraph code“ TECHNOLOGICALNOVELTY”

1909 - ist practical use- ships began to carry wireless radio telegraph

1906 - transmit voice and sound

1915 - 1921 - unlicensed stations

PROCESS OF MODULATION

ANAMWAVE

NOTE: carrier frequency remains constant during the process but that its amplitude variesin accordance with the modulating signal

ENVELOPE - imaginary line of the carrier waveform which is the same as themodulating signal

MATHEMATICAL REPRESENTATION

eE mcE

WHERE:E = peak amplitude of the AM wavee = instantaneous modulating voltage

Instantaneous amplitude of the resulting AM wave:

)sin( tEe c

tmt

mte mc

cmc

ccc

EEE )cos(2

)cos(2

sin

FREQUENCY SPECTRUM with regarding BANDWIDTH

3 FREQUENCIES PRESENT in AM wave1. Carrier frequency - fc2. Lower sideband frequency - LSB (fc-fm)3. Upper sideband frequency - USB (fc+fm)

SPECTRUMANALYZER

V carrier

LSB(mE/2) USB(mE/2)* the voltage of either of the sideband will not

exceed half of the voltage of the CARRIERF

fc-fm fc fc+fm

BW

fmBW 2

Standard AM in Time Domain- modulating voltage is ALWAYS LESS than the CARRIER VOLTAGE* signal distortion OVERMODULATION* interference from adjacent channel

MODULATION INDEX (m)- coefficient of modulation;depth of modulation- describe the amount of amplitude change in an AM waveform

EE

c

mm EEEEm

minmax

minmax

2minmax EEEm

2minmax EEE c

OSCILLOSCOPE : peak or max voltage

RMS VOLTAGE : effective or DC voltage =2V p = 0.707 Vp

AVERAGE VOLTAGE: Vave = 0.636 Vp = 0.318 Vp

HOMEWORK:

Show or derive the power formula, current formula , voltage formula , modulationindex and research the formula of percent modulation and total power involving Pc,Plsb and Pusb...

CURRENT,VOLTAGE,POWER RELATIONSHIP