Principles of Communications BSECE IV - 2
PRINCIPLES OF COMMUNIC!IONS messages Communication – it is the process of sending and receiving messages or information from one location to another via some communication link. Components of a Communication S"stem
1. !ransmitter – it is the source of information. information. It processes the the information so as to make it suitable suitable for transmission and subsequent subsequent reception. It performs encoding and modulation. 2. !ransmission C#annel – provides a means of transporting signal between between transmitter and receiver. receiver.
It
3. Recei$er – – a device that accepts the transmitted signals from the transmission medium and then converts back to their original form. performs decoding and demodulation.
PRINCIPLES OF COMMUNIC!IONS messages Communication – it is the process of sending and receiving messages or information from one location to another via some communication link. Components of a Communication S"stem
1. !ransmitter – it is the source of information. information. It processes the the information so as to make it suitable suitable for transmission and subsequent subsequent reception. It performs encoding and modulation. 2. !ransmission C#annel – provides a means of transporting signal between between transmitter and receiver. receiver.
It
3. Recei$er – – a device that accepts the transmitted signals from the transmission medium and then converts back to their original form. performs decoding and demodulation.
Brief %istorical Bac&'roun(
1820 –Danish physicist H. C. Oersted showed that an electric current produces magnetic field. 1831 –British physicist Michael Faraday discovered that the magnet in motion can generate electricit electricit.. 1 1883! –Samuel Morse invented the Telegraph. 18"# –James Clark Maxell predicted the Theory o! became the theoretical basis of radio. "lectromagnetism which 18!" – #lexander $raham Bell Bell invented the Telephone. 188! –Heinrich %udol! Hert& demonstrated the effect of radio in space. $e showed that radio waves can be reflected% refracted% diffracted%% etc. diffracted 18&3 –'icola Tesla outlined the basic principle of radio transmission and reception. $e saw the possible use of radio waves in long distance wireless communication. 18&# –$uigliermo Marconi invented the 'arconi (ntenna (ntenna.. $e provid pro vided ed the f irs irstt com comple plete te ss sstem tem of wi wirel reless ess com commun munica icatio tion. n.
1&0" –(ee de Forest invented the triode )acuum tu*es which provide the first tonn of practical electronic amplification and reall opened door for wireless communication. 1&20 –)ommercial radio broadcasting began in *ennslvania. 1&31 –"din Hoard #rmstrong patented +'. 1&3, –'onophonic –'onopho nic +' commercial broadcasting began. 1 –1&#, – *opular use of - /roadcasting. 1& 1 –/ell lab scientists Shockley+ Brattain+ and Bardeen invented the
Transistor.
1&,1 –- /roadcasting reached *hilippines shore. 1&,3 –)olor - sstem was adopted. 1&,! –ussia launches the first world satellite called Sputnik. 1&,8 –,il*ey and 'oyce develop the first I). (( launches their first satellite. 1&"1 –tereo /roadcasting in +' band was adopted.
Communication REASONS FOR MODULATION
To maintain the frequency of the signal To prevent any unwanted energy to interfere with the signal information To reduce the required antenna length For multiplexing To maintain equipment limitation
METHODS OF ANALOG MODULATION
Amplitude modulation Angle modulation Frequency modulation Phase modulation
Communication LIMITATION OF COMMUNICATION SYSTEM
Noise (If noise level becomes too high information is lost! "andwidth of frequency allocated for the transmitted signal
BASIC CONCEPT OF COMMUNICATION Modulation process
of putting low#frequency information (audio signal! onto high frequency carrier (radio signal! for transmission$ Transmission ta%es place at the high frequency which has been modulated to carry low frequency information$
Demodulation process
of separating the low#frequency information signal and high frequency carrier$
Radio Spectrum
Frequency
Wavelength
ELF(Extremely Low Frequency)
30 Hz to 300 Hz
Megametric Waves
VF(Voice Frequency)
300 Hz to 3 KHz
Hectokilometric Waves
VLF(Very Low Frequency)
3 KHz to 30 KHz
Myriametric Waves
LF(Low Frequency)
30 KHz to 300 KHz
Kilometric Waves
F(edium Frequency)
300 KHz to 3 MHz
Hectometric Waves
!F(!igh Frequency)
3 MHz to 30 MHz
Decametric Waves
V!F(Very !igh Frequency)
30 MHz to 300 MHz
Metric Waves
"!F("ltra !igh Frequency)
300 MHz to 3 GHz
Decimetric Waves
S!F(Super !igh Frequency)
3 GHz to 30 GHz
Millimetric Waves
E!F(Extremely !igh Frequency) #n$rared Light
30 GHz to 300 GHz
Centimetric Waves
300 GHz to 3 THz
Decimillimetric Waves
#n$rared Light
3 THz to 30 THz
Centimillimetric Waves
#n$rared Light
30 THz to 300 THz
Micrometric Waves
Vi%i&le Light
300THz to 3 PHz
Decimicrometric Waves
"ltraviolet Light
3 PHz to 30 PHz
'ray%
30 PHz to 300 PHz
amma Ray%
300 PHz to 3 EHz
Co%mic Ray%
3 EHz to 30 EHz
)ECIBELS
7ecibels and the ogarithmic cale •
-he range of powers% voltages and currents encountered in radio engineering is too wide to be epressed on linear scale. )onsequentl% logarithmic scale based on the decibel 4d/% one tenth if a /el 5 is used. -he decibel does not specif a magnitude of a power% voltage or current but in ratio between two values of them. 6ains and losses in circuits or radio paths are epressed in decibels.
7ecibels •
It is a unit that describes a ratio. It is not an absolute unit but rather indicates the relation between two powers. mbol used to indicate the gain of the loss in the sstem.
+ormulas
•
*ain 9 10 log 4output : input5 9 10 log 4* 2 :*15
•
Loss 9 10 log 4input : output5 9 10 log 4* 1:*25 –
ote; 7oubling the power means 3 d/ gains< likewise% halving the power means a 3 d/ loss
(bsolute evel •
it is a logarithmic value that shows the difference between the measured value and the laid down standard value.
tandard alues 4(t the Aero elative evel *oint5 •
Resistance; 9 "00 = 4average value if a + telephone signal line5
•
Po+er ; *9 1 m> 4power produced in a mic% if a ?(@ is strongl spoken5
•
Volta'e; 9 0.!!,
•
Current; I9 1.2& m(
Stan(ar( Values t t#e .ero Relati$e Le$el Point/ •
>ith the standard resistance B "00= ,solute Po+er Le$el 9 10 log *m:1 m>
•
,solute Volta'e Le$el 920 log m:0.!!,
•
,solute Current Le$el 920 log Im:1.2& m( –
ote; (cross a resistance of "00=% the absolute levels of voltage% current% and power have the same value% if the laid down standard values are used. In the field% the absolute power level and absolute voltage level are used for telecom path measurements
)alculation of absolute voltage level with different resistance
•
(bsolute oltage evel910 log 4*m:1m>5 C 10 log 4"00:m5
)alculation of absolute current level with different resistance
•
(bsolute )urrent evel910 log 4* m:1 m>5 C 10 log 4m:"005
)onversion from the power level to the voltage level and vice versa •
10 log 4*m:1m>5 9 10 log 4m:0.!!, 5 C 10 log 4"00:m5
)onversion from the power level to the current level and vice versa •
10 log 4*m:1m>5 9 10 log 4m:0.!!, 5 C 10 log 4m: "005
d/m •
(Bm – absolute power level referred to 1m>. -he term
dbm was originall used for telephone and audio work and% when used in that contet% implies an impedance of "00 =% the nominal impedance of a telephone line. >hen it is desired to define a relative transmission level in a circuit% d/- is preferred.
Dquations; d/m 9 10 log 4 *m : 1m>5 • d/m ± d/ 9 d/m d/m1 ± d/ 9 10d/1:10 ± 10dbm2:10 • ote; 0 d/ m 9 1 m>
•
•
d/v •
(B$ – absolute voltage level% referred to 0.!!, . d/ v is
used in audio work when the impedance is not "00 = and no specific impedance is implied. •
d/v 9 10 log 4 m : 0.!!, 5
d/i •
(Bi – absolute current level% referred to 1.2& m(
at "00 =. •
d/i 9 10 log 4I m : 1.2& m(5
d/v s and d/vps •
(B$ s – absolute voltage level in the sound channel%
referred to 0.!!, •
(B$ps 0 absolute noise voltage level in the sound
channel% referred to 0.!!, and ))I- weighted
d*v – deciels relative to ! volt"
d*v + ,- log (Vm . /V)
d*rn – a #eig$ted circ%it noise &o#er %nit in d' re(erenced to !&W )*+0 d'm, !000 Hz-#$ic$ is 0 d'rn" T$is is t$e noise %nit o( !.. #eig$ting net#ork #$ere t$e old !.. tele&$one $andset #as t$e devise %sed"
d*rn + /- log (0m . /x/- 1/,W)
d*rnc – is #eig$ted noise &o#er in d' rn, meas%red y a noise meas%ring set /C* message #eig$ting" 2ure /3!4 te%t tone 5 d*rnc+d*m6 7F/8 weigthted noi%e5 d*rnc+ d*a6 9 9-/8:F/8 weighted5 d*rnc+ d*a6 9 * T$e d'rn 30kHz 1at noise meas%rements are noise readings taken #it$ a 2lter t$at $as a 1at res&onse (rom 0Hz to 30kHz" 4t #as (o%nd to e ty&ically !"5 d' t$an d*rnc readings (or e6%al noise &o#er level"
d/rn)0 Is
noise measure in d/ rn) also referred to Eero transmission level point. d/rn)09 d/rn) F -*d/
p>p picowatt
of noise power% psopometricall weighted. I p>p 9 800 $E tone at F&0 d/ m -his unit is used in psopometric noise weighting% which assumes a perfect receiver thus the weighing curve corresponds to the frequenc response of the human ear onl. d/rn 9 10 log p>p Gote; F&0 d/m 9 110F12 > 9 0 d/ rn)
d/mp ( unit
of noise power in d/ m% measured with psophometric weighting. d/mp 9 10 log p>p : 10 F3 d/mp 9 10 log p>p F &0 9 d/a – 8# 9 d/m – 2., 4for flat noise 300F3#00 $E5
•
d/r Fmeans d/ Hrelative level. Jsed to define transmission level at various points in a circuit or sstem referred to the Eero relative level point. d/r 9d/mFd/m0
•
•
d/m0 – d/m referred to or measured m easured at% a point of Eero transmission level d/m09d/mFd/r d/m0p – the abbreviation for absolute noise power referred to or measured m easured at a point Eero relative transmission level % psophometricall weighted. d/m0p9d/mpFd/r
d/a • • • •
tands for d/ adKusted. It is an epression of the relative loudness of sounds in air as perceived b the human ear. -his is a weighted circuit noise power referred to F8, d/m% which is 0 d/a or 10 F11., It is measured with a noise meter at the receiving end.
-he
meter is calibrated on a 1000 $E tone such that 1m> 40 d/m5 gives a reading of C8, d/m. If 1m> is spread over the band 300F3#00 $E as random white noise% the meter will read as F82 d/m or 0 d/a. -he main advantages with d/( are; adapted
to the human ear response to sound possible to measure with low cost instruments
*ure 1 k$E test tone ;
d/a9d/mC8,
( 3 k$E band of random d/a9d/mC82 noise ; "01(:+1( weighted ; d/a9d/mC!!
d/a0 Is
referred to as circuit noise power in d/ a at a point of Eero relative transmission level 40 d/5. It is preferable to convert circuit noise measurement values from d/a to d/a0 as this makes it unnecessar to know or state the relative transmission level at the point of measurement. d/a09 d/a C -*d/
d/v0 Is
defined as the absolute voltage level% and also referred to the relative level. d/v0 9 d/v C d/r
d/d – used for epressing the gain of an antenna referred to a dipole. d/i – used for epressing the gain of an antenna referred to an isotropic radiator.
-$D D*D ( transmission unit used in number of orthern Duropean countries. p 9 L loge 4*2:*15 Note ; 1 p 9 8."8"d/
MID ((NI
MID ((NI •
oise in communication sstem originates both in the channel and in the communication equipment. oise consist of undesired signals and inhibit communications. It cannot be avoided completel% but its effects can be reduced b various means% such as reducing signal bandwidth% increasing the transmitter power% and using low noise amplifiers for weak signals.
MID ((NI •
• •
oiseF an unwanted form of energ tending to interfere with the eas reception and reproduction of wanted signals. 7istortionF an deviation in the signal caused b the imperfect response of the sstem to the desired signal. InterferenceFis an contamination b eternal signals from human sources% other transmitter% power lines% switching circuits and others.
D++D)- M+ MID 1. imits the performance of ever sstems. 2. It affects the sensitivit of the sstem. 3. It limits the range of the sstem for a given transmitter power. #. It forces a reduction in the bandwidth of the sstem.
MJ)D M+ MID (. Dternal noiseF noise that is generated outside the receiver or circuit. 1.
(tmospheric noiseF noise that come from natural disturbances occurring in the atmosphere. Mften called static electricity . D. ightning charges4O20'$E not significant5
2.
Dtraterrestrial:7eep space noiseF noise from the outer space48 to 1.,6$E5. -his energ components are absorbed b the earths atmosphere before the can reach the atmosphere. • •
3.
olar noiseF generated directl from the suns heat. )osmic:/lackFbod noiseF noise created b the stars.
'anFmade:Industrial noiseF the most troublesome form of noise that is usuall produced b mankind. D. *ower lines% fluorescent lights% electric motors power generating and switching equipments% spark producing mechanism etc.
/. Internal noiseF noise introduced b the receiver itself. 1.
-hermal:Pohnson:/rownian:>hite:6aussian noiseF noise generates due to the rapid and random movements of electrons% atoms% molecules inside a resistive component due to thermal agitation. *n9k-/> *no9k-
>here% *n9 noise power *no9 noise power densit B 1$ E -9 temperature% kelvin k9 /oltEmans constant 41.38 10 F23 P:k5 o that% n9 Q#k-/> In9 Q#k-/>6
MID 7JD -M DD( MJ)D •
•
ois resistors in series% n-9Q#k-/>-series In-9Q#k-/>6-series n-9Q2n1C 2n2CR.C2nn ois resistors in parallel n-9Q#k-/>-parallel In-9Q#k-/>6-parallel In-9QI2n1CI2n2CR.I2nn
7$ot noise8 transistor noise •
•
Ca%sed y random variations in t$e arrival o( electrons or $oles at t$e o%t&%t electrode o( an am&li(ying device and a&&earing as a randomly varying noise c%rrent s%&erim&osed on t$e o%t&%t" 7$ot noise is d%e to t$e cor&%sc%lar nat%re o( trans&ort" 4n !+!9, W:;TE< 7CH=TTK> discovered s$ot noise in t%es and develo&ed 7c$ottky?s t$eorem" 7$ot noise is always associated #it$ direct c%rrent 1o#"
7$ot noise8 transistor noise •
Transit time noise •
•
@oise d%e to t$e time taken y t$e electrons to travel (rom t$e emitter to t$e collector o( t$e transistor 4ts greatest eAect is a $ig$er (re6%encies &artic%larly in t$e micro#ave region" 4t is ot$er#ise kno#n as /H4GH*B @=47E
Blicker noise • •
• •
@oise a&&earing at (re6%encies elo# ! kHz Directly &ro&ortional to emitter c%rrent F%nction tem&erat%re and inversely &ro&ortional to (re6%ency @egligile at ao%t aove 500 Hz Kno#n as ;=W B @=47E, ECE77 @=47E, M=D;:T4=@ @=47E or P4@K @=47E
i%cellaneou% noi%e
Harmonic distortion • • • •
=cc%rs #$en %n#anted $armonics o( a signal are &rod%ced t$ro%g$ non linear am&li2cation Harmonics are integer m%lti&les o( t$e original in&%t signal Total $armonic distortion is $ardly &erce&tile to t$e $%man ear Every com&onent adds some level o( distortion, %t most distortion is insigni2cant
Harmonic distortion •
4ntermod%lation distortion • • •
=cc%rs #$en %n#anted s%m and diAerence (re6%encies are &rod%ced Ca%sed y non*linear e$avior o( t$e signal &rocessing eing %sed Creates additional signals at (re6%encies t$at are t$e s%m and diAerence (re6%encies o( t$e original (re6%encies and at m%lti&les o( t$ose s%m and diAerence (re6%encies"
Frequency Spectrum of intermodulation distortion in a radio-frequency signal passed through the linear broadband amplier.
4m&%lse noise •
C$aracterized y $ig$ am&lit%de &eaks o( s$ort d%ration in t$e total noise s&ectr%m • Consists o( s%dden %rsts o( irreg%larly s$a&ed &%lses t$at generally last et#een a (e# microseconds and several milliseconds
Partition noise •
=cc%rs #$enever c%rrent $as to divide et#een t#o or more electrodes and res%lts to random 1%ct%ations in t$e &rocess
'%rst noise • •
•
;o# (re6%ency noise (o%nd in transistors 4t a&&ears as a series o( %rst o( t#o or more levels o( discrete voltage or c%rrent levels, as $ig$ as several $%ndred microvolts, at random and %n&redictale times :lso called as /P=PC=<@ @=47E
Burst Noise
:valanc$e noise •
arge noise spikes present in the avalanche current due to the oscillation that results in the avalanching action
ignal to oise atio elative measure of the desired signal power to the output noise power. Identifies the noise content at a specific point but not useful in relating how much additional noise is inKected to the circuit. -he higher the value% the better the sstem is. : 9 *s : *n : 9 10 og 4 *s : *n 5
or
: 9 20 og 4 s : n 5
oise +igure : oise +actor: oise ation Jsuall used to specif eactl how nois a device is. It is a figure of merit% indicating how much a component% stage% or series of stages degrades the signal to noise ratio of a sstem. -he noise figure of a totall noiseless device is 1 or 0 d/. -he higher the noise figure% the worse the signal to noise ration at the output. 9 Input 4 : 5 : Mutput 4 : 5 +d/ 9 10 log 4 : 51 : 4 : 50 9 10 log
