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ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%
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INSTRUCTION: Select the correct answer for each of the following questions. Mark only one answer for each item y sha!ing sha!ing the o" corres#on!in corres#on!ing g to the letter letter of your choice on the answer sheet #ro$i!e!. %!R$C!L& #" ER(%,RE% (LL"E). Use #encil no. % only. NOT&:
'hene$er you come across a caret ()* sign+ it means e"#onentiation. e"#onentiation. % &". ")% means " , ("-y*)("/* means ("-y* raise! to the ("/*. 0i12.3435
3. 'hat is the frequency !ifference (in M6/* etween the aural an! $isual carriers in
System 789 ;. <. <.< M6/ =
7. 5.< M6/
C. >.< M6/
?. @.< M6/
%. 0ulse mo!ulation consists essentially of sam#ling analog information signals an!
then con$erting those sam#les into !iscrete #ulses an! trans#orting the #ulses from a source source to a !estinat !estination ion o$er a #hysical #hysical transmiss transmission ion me!ium. me!ium. One of the four #re!ominant metho!s of #ulse mo!ulation is #ulse am#litu!e mo!ulation (0;M*. 'ith 0;M+ the am#litu!e of a constant wi!th+ constant#osition constant#osition #ulse is $arie! accor!ing to the am#litu!e of the sam#le of the analog signal. 'hich is not a !isa!$antage !isa!$antage of 0;M com#are! to other #ulse mo!ulation techniques ;. The an!wi!t an!wi!th h nee!e! for transmis transmission sion of 0;M signal is $ery $ery large large com#are! com#are! to its ma"imum frequency content. 7. The am#li am#litu! tu!e e of 0;M 0;M #ulse #ulses s $arie $aries s accor accor!i !ing ng to mo!u mo!ulat latin ing g signa signal. l. Ther Therefo efore re interference of noise is ma"imum for the 0;M signal an! this noise cannot e remo$e! $ery easily. C. Since am#litu!e am#litu!e of 0;M signal signal $aries+ $aries+ this also $aries $aries the #eak #ower #ower require! require! y the transmitter with mo!ulating signal. ?. 0;M ecomes ecomes inefficient inefficient for signals signals with with $ery high high frequencies.= frequencies.= 2. I!entify the out#ut #ro!uce! from the system shown elow.
;. T?M
7. A?M
C. 0;M
?. 0CM=
4. ; tele$ision transmitter actually transmits two signals at once. They are
;. 7. C. ?.
;n am#litu!emo!ul am#litu!emo!ulate! ate! $i!eo signal signal an! frequencym frequencymo!ulate! o!ulate! au!io au!io signal= signal= Two am#litu!e am#litu!emo!ulate mo!ulate! ! signals: signals: $i!eo $i!eo an! an! au!io ;n am#litu!emo!ul am#litu!emo!ulate! ate! au!io signal signal an! frequencym frequencymo!ulate! o!ulate! $i!eo $i!eo signal Two frequency frequencymo!ulate mo!ulate! ! signals: signals: $i!eo $i!eo an! an! au!io
<. One kilowatt is su##lie! to a rhomic antenna which results in a fiel! strength of
%B D8m at at the recei$ing recei$ing station. station. In or!er to to #ro!uce #ro!uce the same fiel! strength strength at the recei$ing station+ a halfwa$e antenna+ #ro#erly oriente! an! locate! near the rhomic+ must e su##lie! with 35.5 k'. 'hat is the gain of the rhomic ;. 3%.% !7 =
7. %3.% !7
C. 3<.% !7
?.%<.3 !7
5. In an asynchronous !ata system
;. 7oth sen!er an! an! recei$er recei$er are e"actly synchroni synchroni/e! /e! to the same clock clock frequency. frequency. 7. &ach com#uter com#uter wor! is #rece!e! #rece!e! y a start it it an! followe! followe! y a sto# it to frame frame the wor!.= C. The recei$er recei$er !eri$es !eri$es its clock clock signal from from the recei$e! recei$e! !ata !ata stream. stream. ?. ;ll ;ll the the ao$ ao$e. e. >. The squarelaw relationshi# of the A&Ts in#ut $ersus out#ut
;. 7. C. ?.
;llows for for greater greater sensiti$ity sensiti$ity in an AM recei$er 0ro$i!es 0ro$i!es im#ro$e im#ro$e! ! noise #erform #erformance ance Re!uce Re!uces s shot shot nois noise e Minimi/e Minimi/es s crossmo crossmo!ula !ulation tion= =
electrical length of stan!ar! stan!ar! R9@8U coa"ial cale woul! e require! to otain @. 'hat electrical a 4
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ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%
;. B.B@%< m=
%E! B
7. B.35< m
C. B.B432 m
?. B.3%< m
F. ;n analog signal is an!limite! to 4 k6/+ sam#le! at the Nyquist rate an! the
sam#les are quanti/e! into 4 le$els. The quanti/e! le$els are assume! to e in!e#en!ent an! equally #roale. If we transmit two quanti/e! sam#les #er secon!+ the information rate is ;. 3 it8sec
7. % its8sec
C. 2 its8sec
?. 4 its8sec=
3B. It is a form of storean!forwar! network. ?ata+ inclu!ing source an! !estination
i!entification co!es+ are transmitte! into the network an! store! in a switch. &ach switch within the network has message storage ca#ailities. The network transfers the !ata from switch to switch when it is con$enient to !o so. Consequently+ !ata are not transferre! in real time, there can e a !elay at each switch. 'ith this switching cannot occur+ locking cannot occur. ;. circuit switching
7. message switching=
C. #acket switching ?. co!e switching
33. 'hat is the im#e!ance seen at the in#ut when transmission line is shorte!
;. infinity
7. GHocot(Jl*
C.B
?.
GHotan(Jl* =
3%. Network to#ology !escries the layout or a##earance of a networkKthat is+ how the
com#uters+ cales+ an! other com#onents within a !ata communications network are interconnecte!+ oth #hysically an! logically. 'hat network to#ology is consi!ere! a multi#oint !ata communications circuit that makes it relati$ely sim#le to control !ata flow etween an! among the com#uters ecause this configuration allows all stations to recei$e e$ery transmission o$er the network 'ith this to#ology+ all the remote stations are #hysically or logically connecte! to a single transmission line. The two en!s of the transmission line ne$er touch to form a com#lete loo#. It is the sim#lest an! most common metho! of interconnecting com#uters. ;. us=
7. mesh
C. star
?. ring
32. Stan!ingwa$e ratio (S'R* is a mathematical e"#ression of the nonuniformity of an
electromagnetic fiel! (&M fiel!* on a transmission line such as coa"ial cale. Usually+ S'R is !efine! as the ratio of the ma"imum ra!iofrequency ( RA* $oltage to the minimum RA $oltage along the line. This is also known as the $oltage stan!ing wa$e ratio (DS'R*. The S'R can also e !efine! as the ratio of the ma"imum RA current to the minimum RA current on the line (current stan!ingwa$e ratio or IS'R*. 'hat is the i!eal $alue of S'R ;. /ero 7. infinite
C. one= ?. equal to reflection coefficient
34. Reflection coefficient is a #arameter that !escries how much of an
electromagnetic wa$e is reflecte! y an im#e!ance !iscontinuity in the transmission me!ium. It is the ratio of the com#le" am#litu!e of the reflecte! wa$e to that of the inci!ent wa$e. In #articular+ at a !iscontinuity in a transmission line+ it is the com#le" ratio of the electric fiel! strength of the reflecte! wa$e to that of the inci!ent wa$e. This is ty#ically re#resente! with a L. 'hich of the following is false aout reflection coefficient ;. ; reflection coefficient of /ero means that the characteristic im#e!ances of two transmission lines connecte! together are equal. Therefore+ #ower transfer is ma"imum. 7. The worst $alue for reflection coefficient is 3. C. Reflection coefficient can e im#ro$e! y using quarter wa$elength im#e!ance transformer. ?. 'hen the characteristic im#e!ance of the transmission line is not matche! with the im#e!ance of the antenna to which it is connecte!+ the reflection coefficient ecomes infinite.=
3<. ?ualtone multifrequency (?TMA* is a sim#le twoofeight enco!ing scheme where each
!igit is re#resente! y the linear a!!ition of two frequencies. It is a more efficient means of !ialing than !ial #ulsing for transferring tele#hone numers from a suscriers location to the central office switching machine. Its main a!$antage is s#ee! an! control. It was originally calle! TouchTone. Su##ose you #ress F+ this will e equi$alent to what #air of frequencies ;. @<% 6/ an! 3225 6/ 7. @<% 6/ an! 34>> 6/=
C. F43 6/ an! 34>> 6/ ?. F43 6/ an! 3225 6/
35. It is a #ulse of a !irectsequence s#rea! s#ectrum (?SSS* co!e+ such as a 0seu!o
ran!om Noise (0N* co!e sequence use! in !irectsequence co!e !i$ision multi#le access (C?M;* channel access techniques
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;. flake 7. it C. nile ?. chi# = 3>. It is a re!un!ancy error !etection scheme that uses #arity to !etermine if a transmission error has occurre! within a message an! is therefore sometimes calle! message #arity. 'ith this re!un!ancy scheme+ each it #osition has a #arity it. ;. PRC= 7. DRC C. checksum ?. CRC 3@. Three common switching techniques are use! with #ulic !ata networks: circuit switching+ message switching+ an! #acket switching. 0acket switching in$ol$es !i$i!ing !ata messages into small un!les of information an! transmitting them through communications networks to their inten!e! !estinations using com#uter controlle! switches. 'hy is it faster to sen! #ackets of a fi"e! si/e com#are! to #ackets of $ariale si/e ;. Only #ackets of a fi"e! si/e are com#atile for #arallel transmission. 0ackets of $ariale si/e are com#atile to series transmission only. 7. The #rocessing require! to store an! forwar! #ackets of !ifferent lengths is greater than that require! for #ackets of a fi"e! length.= C. 0ackets of $ariale si/e nee! start an! sto# its while #ackets of fi"e! si/e !ont. ?. None of these. 7oth #ackets of $ariale si/e an! #ackets of fi"e! si/e require equal transmission time. 3F. 'hen a transmission line is terminate! in either a short or an o#en circuit+ there
is an im#e!ance in$ersion e$ery quarterwa$elength. Aor a lossless line+ the im#e!ance $aries from infinity to /ero. 6owe$er+ in a more #ractical situation where #ower losses occur+ the am#litu!e of the reflecte! wa$e is always less than that of the inci!ent wa$e e"ce#t at the termination. Therefore+ the im#e!ance $aries from some ma"imum to some minimum $alue or $ice $ersa+ !e#en!ing on whether the line is terminate! in a short or an o#en. 'hich of the following statements is false regar!ing transmission line ;. ; quarterwa$elength+ short circuite! transmission line has ma"imum im#e!ance. 7. ; halfwa$elength+ o#en circuite! transmission line has ma"imum im#e!ance. C. ; transmission line less than one quarterwa$elength long an! short circuite! will a##ear ca#aciti$e.= ?. ; transmission line more than one halfwa$elength long an! o#en circuite! will a##ear in!ucti$e. %B. The in#ut to an AM recei$er has a S8N of %.@. 'hat is the frequency !e$iation cause!
y the noise if the mo!ulating frequency is 3.< k6/ an! the #ermitte! !e$iation is 4 k6/ ;. <4>.@ 6/=
7. 52<.3 6/
C. F@2.< 6/
?. %F@.% 6/
%3. ; 0PP is set u# such that its DCO freeruns at 3B M6/. The DCO !oes not change
frequency until it is within
reflection. This ha##ens when light or any electromagnetic wa$e tra$els from one me!ium to another with !ifferent refracti$e in!ices. It is also require! that the inci!ent angle e less than the critical angle for total internal refraction to occur. 'hat is meant y critical angle ;. Critical angle is the angle at which light is refracte!. 7. Critical angle is the angle at which light ecomes in$isile. C. Critical angle is the angle at which light has gone from the refracti$e mo!e to the reflecti$e mo!e.= ?. Critical angle is the angle at which light has crosse! the oun!ary layers from one in!e" to another. %2. ;n earth mat for a communication tower consists of ;. one or two ra!ials e"ten!ing from ase of tower at a !e#th of aout < cm elow groun! 7. a large numer of ra!ials e"ten!ing from ase of tower at a !e#th of aout 2 m C. a large numer of ra!ials e"ten!ing from ase of tower at a !e#th of aout 2B cm = ?. none of the ao$e %4. Aor
an o#tical !etermine the transmissions.
fier 3B ma"imum
km long !igital
with a #ulses#rea!ing constant of < ns8km+ transmission rates for Nonreturnto/ero
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ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%
;. %B M#s
7. 3B M#s=
%E! B
C. < M#s
?.
%<. 'hich one of the following is nonresonant antenna
;. Aol!e! !i#ole
7. 7roa! si!e array
C. &n! fire array
?. Rhomic antenna=
%5. Microstri# is a flat con!uctor se#arate! y an insulating !ielectric from a large
con!ucting groun! #lane. The microstri# is usually onequarter or onehalf wa$elength long. ;s the !istance etween co##er trace an! the groun! #lane increases+ the $alue of the characteristic im#e!ance of your stri#line ;. increases= 7. remains constant
C. !ecreases ?. o is tem#erature !e#en!ent
%>. 9erman astronomer ohannes e#ler !isco$ere! the laws that go$ern satellite motion.
e#lers laws can e a##lie! to any two o!ies in s#ace that interact through gra$itation. The larger of the two o!ies is calle! the #rimary an! the smaller is calle! the secon!ary or satellite. e#lers secon! law is known as the Paw of ;reas. It states that for equal inter$als of time+ a satellite will swee# out equal areas in the orital #lane+ focuse! at the arycenter (the center of mass of the #rimary*. 'hat conclusion can e !rawn from e#lers secon! law ;. The $elocity of a satellite will e greatest at the #oint of closest a##roach to earth an! least at the farthest #oint.= 7. The $elocity of a satellite will e least at the #oint of closest a##roach to earth an! greatest at the farthest #oint. C. The $elocity of a satellite !oes not change regar!less of its #osition relati$e to the earth. ?. Aorget it. e#lers secon! law has nothing to !o with the $elocity of the satellite. %@. 'hy !o CSM;8C? #ackets ha$e a minimum si/e limit
;. If a #acket is too short+ no!es at either en! of #acket+ an! get off efore the #ackets tra$el collision woul! not e !etecte!.= 7. If a #acket is too short+ no!es at either en! of collision can easily ha##en. C. If a #acket is too short+ no!es at either en! of #acket+ an! get off efore the #ackets tra$el collision woul! e !etecte! ut cannot e a$oi!e!. ?. None of these. CSM;8C? #ackets !ont ha$e a minimum
a cale coul! get on+ sen! a far enough to colli!e. The a cale coul! not get on as a cale coul! get on+ sen! a far enough to colli!e. The si/e limit.
%F. ; #ointto#oint communication system consists of a transmitter o#erating at 4BB M6/
with an RA out#ut of FB '. It is fe! to a 5 !7i antenna through a 3
!7 #er 3BB ft. The recei$ing stations+ locate! se$eral miles away+ has an antenna system consisting of F !7 gain antenna+ with a 3BB ft coa"ial cale with an attenuation of 3.< !7 #er 3BB ft. if the #ath loss etween the transmitter an! recei$ing stations is 3%4 !7+ !etermine the signal le$el in !7m at the recei$er. ;. [email protected] !7m
7. <<.43 !7m
C. 52.<3 !7m
=
?.
5B.<> !7m
2B. In electroacoustics+ what !o you call the equation show to measure re$ereration
time
;. Saine &quation 7. Ste#hens 7ates &quation
C. Norris G&yring &quation = ?. 7ose &quation
23. ; lou!s#eaker #ro!uces an S0P of @
#ower of 3 '. 6ow lou! is the S0P at !istance of %B meters if this s#eaker is !ri$en to 3B ' of electrical #ower ;.
7. 5F !7S0P =
C. >F !7S0P
?. 5F !7S0P
2%. The recei$ing installation whose 98T was foun! to e %B.5 !7 is use! as a groun!
terminal to recei$e a signal from a satellite at a !istance of 2@+BBB km. The satellite has a transmitter #ower of
7. 5.>B !7
C. 2%.23 !7
?. >.5B !7
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22. There
are two !e$ices commonly use! to !etect light energy in fiero#tic communications recei$ers: 0IN !io!es an! ;0?s. The most im#ortant characteristics of light !etectors are state! elow. I!entify the false statement. ;. Responsi2it34 It is the measure of the con$ersion efficiency of a #hoto!etector. It is the ratio of the out#ut current of a #hoto!io!e to the in#ut o#tical #ower an! has the unit of am#eres #er watt. It is generally gi$en for a #articular wa$elength or frequency. 7. )ar5 current4 The leakage current that flows through a #hoto!io!e with no light in#ut. Thermally generate! carriers in the !io!e cause !ark current. C. !ransit time4 The time it takes a lightin!uce! carrier to tra$el across the !e#letion region of a semicon!uctor. This #arameter !etermines the ma"imum it rate #ossile with a #articular #hoto!io!e. ?. Light sensiti2it34 The ma"imum o#tical #ower a light !etector can recei$e an! still #ro!uce a usale electrical out#ut signal. Pight sensiti$ity is generally gi$en for a #articular wa$elength in either !7m or !7. =
24. Su##ose there is an ostacle mi!way etween the transmitter an! recei$er o$er a
!istance of 4
!ecrease increase !ecrease increase
of of of of
%F.>%V %F.>%V 35.@
from from from from
the the the the
original original original original
$alue $alue $alue = $alue
2<. Aor 3B it 0CM system+ the signal to quanti/ation noise ratio is 5% !7. If the
numer of its is increase! y %+ then the signal to quanti/ation noise ratio will ;. increase! y 5 !7 7. increase! y 3% !7 =
C. !ecrease! y 5 !7 ?. !ecrease! y 3% !7
25. 'hat is the main !ifference with 0reem#hasis an! ?eem#hasis in AM 7roa!casting
;. 0reem#hasis is increasing the relati$e strength of lowfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is !ecreasing the relati$e strength of lowfrequency com#onents of the out#ut signal of an AM !etector in an AM recei$er. 7. 0reem#hasis is !ecreasing the relati$e strength of lowfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is increasing the relati$e strength of lowfrequency com#onents of the out#ut signal of an AM !etector in an AM recei$er. C. 0reem#hasis is !ecreasing the relati$e strength of highfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is increasing the relati$e strength of highfrequency com#onents at the out#ut signal of an AM !etector in an AM recei$er. ?. 0reem#hasis is increasing the relati$e strength of highfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is !ecreasing the relati$e strength of highfrequency com#onents at the out#ut signal of an AM !etector in an AM recei$er.= 2>. The resistance of any wire con!uctor+ whether it is a resistor or ca#acitor lea! or
the wire in an in!uctor+ is #rimarily !etermine! y the ohmic resistance of the wire itself. 6owe$er+ other factors influence it. The most significant one is skin effect+ the ten!ency of electrons flowing in a con!uctor to flow near an! on the outer surface. ;s the skin effect increases+ what ha##ens to the resistance of the wire ;. increases=
7. no change
C. !ecreases
?. no effect
2@. Single
Si!ean! was mathematically recogni/e! an! un!erstoo! as early as 3F34, howe$er+ not until 3F%2 was the first #atent grante! a! a successful communication link estalishe! etween &nglan! an! Unite! States. One common !esignation assigne! y International Telecommunication Union (ITU* is C2A !esignation. ?escrie this configuration. ;. (' $ndependent %ideband 6$%B74 It is a form if am#litu!e mo!ulation in which a single carrier frequency is in!e#en!ently mo!ulate! y two mo!ulating signals. In essence+ IS7 is a form of !oule si!ean! transmission in which the transmitter consists of two in!e#en!ent singlesi!ean! su##resse! carrier mo!ulators.
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7. (' 8estigial %ideband4 It is a form of am#litu!e mo!ulation in which the carrier an! once com#lete si!ean! are transmitte!+ ut only #art of the secon! si!ean! is transmitte!. The carrier is transmitte! at full #ower. Consequently+ the lower frequencies can a##reciate the enefit of 3BBV mo!ulation+ whereas the higher frequencies cannot achie$e more than the effect of
an! software of e"isting ase stations. It allows for nine !ifferent (autonomously an! ra#i!ly selectale* air interface formats. It is known as multi#le mo!ulation an! co!ing scheme (MCS*+ with $arying !egrees of error control #rotection. 'hat is this that was !e$elo#e! from the !esire of 9SM an! IS325 o#erators to ha$e a common technology #ath to e$entual 29 high s#ee! !ata access ;. PT&
7. &?9&=
C. %.<9
?. 90RS
4B. It #ro$i!es in!e#en!ence to the a##lication #rocesses y a!!ressing any co!e or
synta" con$ersion necessary to #resent the !ata to the network in a common communications format. It s#ecifies how en!user shoul! format the !ata. This layer #ro$i!es for translation etween local re#resentations of !ata an! the re#resentation of !ata that will e use! for transfer etween en! users. The results of encry#tion+ !ata com#ression+ an! $irtual terminals are e"am#les of the translation ser$ice. ;. Session Payer
7. 0resentation Payer=
C. Trans#ort Payer
?. 0hysical layer
43. Aor a inary AS mo!ulator with s#ace+ rest+ an! mark frequencies of 5B+ >B+ an! @B
M6/+ res#ecti$ely an! an in#ut it rate of %B M#s+ !etermine the out#ut au! an! the minimum require! an!wi!th. ;. 7'15B M6/+ au! rate1 %B Mau! = 7. 7'1@B M6/+ au! rate1 %B Mau!
C. 7'1>B M6/+ au! rate1 %B Mau! ?. 7'15B M6/+ au! rate1 2B Mau!
4%. The half wa$e !i#ole is forme! from a con!ucting element which is wire or metal tue
which is an electrical half wa$elength long. It is ty#ically fe! in the centre where the im#e!ance falls to its lowest. In this way+ the antenna consists of the fee!er connecte! to two quarter wa$elength elements in line with each other. The $oltage an! current le$els $ary along the length of the ra!iating section of the antenna. This occurs ecause stan!ing wa$es are set u# along the length of the ra!iating element. ;t the fee!#oint of this antenna+ the current is ;. ma"imum=
7. minimum
C. remains constant ?. /ero current
42. ; fee!ack oscillator is an am#lifier with a fee!ack loo# (i.e. #ath for energy to
#ro#agate generates where it statement
from the out#ut ack to the in#ut. Once starte!+ a fee!ack oscillator an ac out#ut signal of which a small #ortion if fe! ack to the in#ut+ is am#lifie!. ;mong the following statements+ which of the following is not a requirement for a fee!ack oscillator to work
;. (mplification4 ;n oscillator circuit must inclu!e atleast one acti$e !e$ice an! e ca#ale of $oltage am#lification. In fact+ at times+ it may e require! to #ro$i!e infinite gain. 7. Positi2e 9eedbac54 ;n oscillator must ha$e a com#lete #ath for a #ortion of the out#ut signal to e returne! to the in#ut. The fee!ack must e !egenerati$e. If the #hase is incorrect of the am#litu!e is insufficient+ the oscillation will saturate. = C. 9reuenc3-determining components . ;n oscillator must ha$e frequency!etermining com#onents such as resistors+ ca#acitors+ in!uctors+ or crystals to allow frequency of o#eration to e set or change!. ?. Po;er source . ;n oscillator must ha$e a source of electrical energy+ such as !c #ower su##ly.
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44. O#en
systems interconnection (OSI* is the name for a set of stan!ar!s for communicating among com#uters. The #rimary #ur#ose of OSI stan!ar!s is to ser$e as a structural gui!eline for e"changing information etween com#uters+ workstations+ an! networks. In the OSI layer+ what is the #ur#ose of session layer ;. The layer is res#onsile for network a$ailaility (i.e.+ !ata storage an! #rocessor ca#acity*. This #rotocol #ro$i!es the logical connection entities at the a##lication layer. These a##lications inclu!e file transfer #rotocols an! sen!ing email. The res#onsiilities inclu!e network logon an! logoff #roce!ures an! user authentication. = 7. It is res#onsile for #ro$i!ing errorfree communications across the #hysical link connecting #rimary an! secon!ary stations (no!es* within a network (sometimes referre! to as ho#toho# !eli$ery*. It #ackages !ata from the #hysical layer into grou#s calle! locks+ frames+ or #ackets an! #ro$i!es a means to acti$ate+ maintain+ an! !eacti$ate the !ata communications link etween no!es. C. It #ro$i!es !etails that enale !ata to e route! etween !e$ices in an en$ironment using multi#le networks+ sunetworks+ or oth. Com#onents that o#erate at this layer inclu!e routers an! their software. It !etermines which network configuration is most a##ro#riate for the function #ro$i!e! y the network an! a!!resses an! routes !ata within networks y estalishing+ maintaining+ an! terminating connections etween them. ?. It #ro$i!es in!e#en!ence to the a##lication #rocesses y a!!ressing any co!e or synta" con$ersion necessary to #resent the !ata to the network in a common communications format. This s#ecifies how en!user a##lications shoul! format the !ata. This layer #ro$i!es for translation etween local re#resentations of !ata an! the re#resentation of !ata that will e use! for transfer etween en! users.
4<. ; line of length less than W84 length an! o#en circuite! at far en! eha$es as
;. an in!uctance 7. a ca#acitance = C. series resonant ?. #arallel resonant 45. In a channel $oice co!er+ the out#uts of si"teen %B 6/ low #ass filters are sam#le!+ multi#le"e! an! ;8? con$erte!. If sam#ling is at 4B sam#les8secon! an! 2 its8sam#le re#resents each $oltage sam#le+ the it rate is aout ;. 3.F k its8sec = 7. B.F< k its8sec C. 2.@ k its8sec ?. >.5 k its8sec 4>. 7an!wi!th utili/ation is the wise use of a$ailale an!wi!th to achie$e s#ecific goals. &fficiency can e achie$e! y multi#le"ing, #ri$acy an! antiHamming can e achie$e! y s#rea!ing. S#rea! s#ectrum achie$es its goals through two #rinci#les: the an!wi!th allocate! to each station nee!s to e+ y far+ larger than what is nee!e!. This allows re!un!ancy. Secon!+ e"#an!ing the original an!wi!th 7 to the an!wi!th 7ss must e !one y a #rocess that is in!e#en!ent of the original signal. In other wor!s+ the s#rea!ing #rocess occurs after the signal is create! y the source. 7y this conce#t+ what is the !ifference of Arequency ho##ing s#rea! s#ectrum an! ?irect Sequence S#rea! S#ectrum ;. The !irect sequence s#rea! s#ectrum (?SSS* technique uses M !ifferent carrier frequencies that are mo!ulate! y the source signal. ;t one moment+ the signal mo!ulates one carrier frequency, at the ne"t moment+ the signal mo!ulates another carrier frequency while frequency ho##ing s#rea! s#ectrum (A6SS* technique e"#an!s the an!wi!th of a signal y re#lacing each !ata it with n its using a s#rea!ing co!e. In other wor!s+ each it is assigne! a co!e of n its+ calle! chi#s. The frequency ho##ing s#rea! s#ectrum (A6SS* technique uses M !ifferent carrier 7. frequencies that are mo!ulate! y the source signal. ;t one moment+ the signal mo!ulates one carrier frequency, at the ne"t moment+ the signal mo!ulates another carrier frequency while !irect sequence s#rea! s#ectrum (?SSS* technique e"#an!s the an!wi!th of a signal y re#lacing each !ata it with n its using a s#rea!ing co!e. In other wor!s+ each it is assigne! a co!e of n its+ calle! chi#s. = The frequency ho##ing s#rea! s#ectrum (A6SS* technique uses M !ifferent carrier C. frequencies that are mo!ulate! y the source signal. ;t one moment+ the signal mo!ulates one carrier frequency, at the ne"t moment+ the signal mo!ulates another carrier frequency while !irect sequence s#rea! s#ectrum (?SSS* technique+ a low it #seu!oran!om co!e is a!!e! to a highit rate information signal to generate a low it rate #seu!oran!om signal closely resemling noise that contains oth the original !ata signal an! the #seu!o ran!om co!e must e known. ?. The !irect sequence s#rea! s#ectrum (?SSS* technique uses M !ifferent carrier frequencies that are mo!ulate! y the source signal. ;t one moment+ the signal
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mo!ulates one carrier frequency, at the ne"t moment+ the signal mo!ulates another carrier frequency while frequency ho##ing s#rea! s#ectrum (A6SS+ a low it #seu!oran!om co!e is a!!e! to a highit rate information signal to generate a low it rate #seu!oran!om signal closely resemling noise that contains oth the original !ata signal an! the #seu!o ran!om co!e must e known. 4@. O#en
systems interconnection (OSI* is the name for a set of stan!ar!s for communicating among com#uters. The #rimary #ur#ose of OSI stan!ar!s is to ser$e as a structural gui!eline for e"changing information etween com#uters+ workstations+ an! networks. In the OSI layer+ what is the #ur#ose of network layer ;. It is res#onsile for #ro$i!ing errorfree communications across the #hysical link connecting #rimary an! secon!ary stations (no!es* within a network (sometimes referre! to as hop-to-hop !eli$ery*. It #ackages !ata from the #hysical layer into grou#s calle! locks+ frames+ or #ackets an! #ro$i!es a means to acti$ate+ maintain+ an! !eacti$ate the !ata communications link etween no!es. 7. The layer is res#onsile for network a$ailaility (i.e.+ !ata storage an! #rocessor ca#acity*. This #rotocol #ro$i!es the logical connection entities at the a##lication layer. These a##lications inclu!e file transfer #rotocols an! sen!ing email. The res#onsiilities inclu!e network logon an! logoff #roce!ures an! user authentication. C. It #ro$i!es !etails that enale !ata to e route! etween !e$ices in an en$ironment using multi#le networks+ sunetworks+ or oth. Com#onents that o#erate at this layer inclu!e routers an! their software. It !etermines which network configuration is most a##ro#riate for the function #ro$i!e! y the network an! a!!resses an! routes !ata within networks y estalishing+ maintaining+ an! terminating connections etween them. = ?. It #ro$i!es in!e#en!ence to the a##lication #rocesses y a!!ressing any co!e or synta" con$ersion necessary to #resent the !ata to the network in a common communications format. This s#ecifies how en!user a##lications shoul! format the !ata. This layer #ro$i!es for translation etween local re#resentations of !ata an! the re#resentation of !ata that will e use! for transfer etween en! users.
4F. It is foun! that in a tele#hone system 5B suscriers initiate calls !uring a 2B
minute inter$al an! the total !uration of all the calls is 3BB minutes. The loa! is ;. % &rlang
7. 2 &rlang
C. 2.222 &rlang =
transmission line terminate! with a loa! resistance transmission lines characteristic im#e!ance has a DS'R of: ;. 3
7. B
that
C. -3 =
?. B.222 &rlang is
equal
to
the
?. infinity
<3. It is foun! that a shi# to shi# communication suffers from fa!ing. This can e
a$oi!e! y using ;. s#ace !i$ersity 7. frequency !i$ersity =
C. roa! an! antenna ?. !irectional antenna
<%. ; tele#hone line has a an!wi!th of 2.% k6/ an! a signal to noise ratio of 2< !7. ;
signal is transmitte! !own this line using a four le$el. 'hat is the ma"imum theoretical !ate rate ;. 4.5k#s
7. 3%.@ k#s =
C. 2>.% k#s
?.3@. 5k#s
<2. ;
!e$ice has two resistances 2BB ohm, an! %BB ohm, res#ecti$ely. The noise $oltages !ue to these two resistance calculate! se#arately are <.2@ D an! 4.2@ D res#ecti$ely. 'hen oth of them are use! together+ the noise $oltage will e ;. F.>5 D
7. 3 D
C. %2.<5 D
?. 5.F4 D =
<4. Consi!er a $i!eo signal that has a resolution of 54B y 4@B #i"els, with a 2B 6/
frame rate an! #rogressi$e scan. The luminance is sam#le! using @ its #er sam#le. The two chroma channels also use @ its #er sam#le+ ut the color resolution is one fourth that use! for luminance. Ain! the a##ro"imate it rate of this signal+ neglecting synchroni/ation+ error correction+ an! com#ression. ;. %>.5< M#s
7. 33B.5 M#s=
C. <<.2 M#s
?. %%3.% M#s
<<. In angle mo!ulation+ the amount of carrier !e$iation is #ro#ortional to the rate of
change of the mo!ulating signal. 'hat is the main !ifference of AM an! 0M mo!ulate! carrier ;. 7oth AM an! 0M a##ear to e frequency mo!ulate! y a cosine of the mo!ulating signal.
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7. 7oth AM an! 0M a##ear to e frequency mo!ulate! signal C. 0M carrier a##ears to e frequencymo!ulate! y signal while AM a##ears to e frequencymo!ulate! signal = ?. AM carrier a##ears to e frequencymo!ulate! y signal while 0M a##ears to e frequencymo!ulate! signal
y a sine of the mo!ulating the cosine of the mo!ulating y the sine of the mo!ulating the cosine of the mo!ulating y the sine of the mo!ulating
<5. The antenna !iameter of a ra!ar system is !oule!. The ma"imum range will
;. e !oule! = 7. e hal$e!
C. ecome four times ?. !ecrease to one fourth
<>. ; ra!io station works at @BB k6/ an! uses ;M. If this is a #ulic roa!cast system+
it shoul! transmit using ;. 7. C. ?.
#araolic reflector to transmit all roun! turnstile antenna for the require! lan! half wa$e long hori/ontal wa$e a $ertical antenna less than quarter for #ractical reasons =
<@. One of recei$er #arameters in a communication system is the selecti$ity. It is a
#arameter that is use! to measure the aility of the recei$er to acce#t a gi$en an! of frequencies an! reHect all others. There are se$eral ways to !escrie the selecti$ity of the recei$er. One common way is to sim#ly gi$e the an!wi!th at two le$el attenuations+ 2!7 an! 5B !7. Thus the ratio of the two an!wi!ths is calle! the sha#e factor. In the recei$er #art of your communication system+ what is the main !ifference etween an o$erly selecti$e an! un!erselecti$e recei$er ;. If a recei$er is o$erly selecti$e only #art of the an!wi!th of the ;M signal is am#lifie!+ causing some of the si!ean! information to e lost an! !istortion results while un!erselecti$e recei$er is more than one ra!io station on !ifferent frequencies may e #icke! u# y the recei$er at the same time. = 7. If a recei$er is un!erselecti$e only #art of the an!wi!th of the ;M signal is am#lifie!+ causing some of the si!ean! information to e lost an! !istortion results while o$erly selecti$e recei$er is more than one ra!io station on !ifferent frequencies may e #icke! u# y the recei$er at the same time. C. If a recei$er is o$erly selecti$e+ the $olume control is tune! u# to ma"imum+ the !esire! station is $ery weak while un!erselecti$e recei$er recei$e! too much noise an! then #icke! u# an! am#lifie! y the recei$er. ?. If a recei$er is un!erselecti$e+ the $olume control is tune! u# to ma"imum+ the !esire! station is $ery weak while o$erly selecti$e recei$er recei$e! too much noise an! then #icke! u# an! am#lifie! y the recei$er.
owner wants to use the same !ish with a new fee!horn+ for u an! (3%96/* satellites. 'hat effect will the change in frequency ha$e on the gain an! eamwi!th of the antenna ;. 9ain !ecreases y F.<4 !7+ eamwi!th !ecreases three times of its former $alue. 7. 9ain increases y F.<4 !7+ eamwi!th !ecreases three times of its former $alue. C. 9ain !ecreases y F.<4 !7+ eamwi!th !ecreases 382 of its former $alue. ?. 9ain increases y F.<4 !7+ eamwi!th !ecreases 382 of its former $alue. = 5B. 'hat is an auto configuration #rotocol use! on I0 networks where com#uters that are connecte! to I0 networks must e configure! efore they can communicate with other com#uters on the network. ;. Re$erse ;!!ress Resolution 0rotocol (R;R0* 7. 7ootstra# 0rotocol (7OOT0* C. In$erse ;!!ress Resolution 0rotocol (I;R0* ?. ?ynamic 6ost Configuration 0rotocol (?6C0*= 53. The DPA+ PA an! MA antennas are ;. hori/ontally #olari/e! C. non linearly #olari/e! 7. $ertically #olari/e! = ?. either (a* or (* 5%. The antenna that is ra!iating electromagnetic energy a##ears to the generator as an
i!eally resisti$e electrical loa! so that the a##lie! #ower is consume! as ra!iate! energy. In a!!ition to the resisti$e com#onent+ an antenna can ha$e a reacti$e com#onent. The resisti$e com#onent is equi$alent to a resistor which+ if use! to
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re#lace the antenna+ woul! !issi#ate #ower equal to the ra!iate! #ower of the antenna. This is known as ;. antenna cou#ler 7. loa!ing coil
C. ra!iation resistance= ?. !ummy loa!
52. ;
transmission line is a metallic con!uctor system use! to transfer electrical energy from one #oint to another using electrical current flow. It is a two or more electrical con!uctors se#arate! y a noncon!ucti$e insulator (!ielectric*+ such as #air of wires or system of wire #airs. 'hen o is not equal to P+ some of inci!ent #ower is asore! y the loa! an! some is reflecte! to the source. This is calle! unmatche! or mismatche! lines. ; nonlossy transmission line terminate! with an o#en circuit will ha$e: ;. ;n in#hase reflecte! current that is equal in magnitu!e to the inci!ent current 7. ;n o##osite#hase reflecte! current that is equal in magnitu!e to the inci!ent current = C. ;n in#hase reflecte! current that is smaller n magnitu!e than the inci!ent current ?. ;n o##osite#hase reflecte! current that is smaller in magnitu!e than the inci!ent current
54. Con$ert the 3% it sam#le 3BB33B3BB3BB into an @ it com#resse! co!e
;. 33B33B3B =
7. 3B333B3B
C. 3333BBB3
?. 3B3B3333
5<. The an!wi!th of a $i!eo signal is 4.< M6/. This signal is to e transmitte! using
0CM with the numer of quanti/ation le$els X 1 3B%4. The sam#ling rate shoul! e %BV higher than the Nyquist rate. Calculate the system it rate ;. <4M#s
7. 3B@ M#s =
C. FB M#s
?. 4< M#s
55. In YYYYYYY enco!ing+ the !uration of the it is !i$i!e! into two hal$es. The $oltage
remains at one le$el !uring the first half an! mo$es to the other le$el in the secon! half. The transition at the mi!!le of the it #ro$i!es synchroni/ation. ;. Manchester 7. ?ifferential Manchester
C. NRP ?. 7oth ; an! 7 =
5>. ; ra!ar transmitter has a #ower of 3B k' an! o#erates at a frequency of F.< 96/. Its
signal reflects from a target 3< km away with a ra!ar cross section of 3B.% square meter. The gain of the antenna is %B !7i. Calculate the recei$e! signal #ower. ;. 3B.3 f'= 7. %2.3 f' C. 2.43 f' ?.F.@ f' 5@. Xuanti/ation is the #rocess of con$erting an infinite numer of #ossiilities to a
finite numer of con!itions. ;nalog signals contain an infinite numer of am#litu!e #ossiilities. Thus+ con$erting an analog signal to a 0CM co!e with a limite! numer of cominations requires quanti/ation. In essence+ quanti/ation is the #rocess of roun!ing off the am#litu!es of flatto# sam#les to a manageale numer of le$els. The !ecimal $alue a!!e! to or sutracte! from the original $alue is consi!ere! an error an! is calle! quanti/ation error. 'hich of the following !ecreases quanti/ation error ;. ?ecrease the numer of le$els 7. ?ecrease the sam#ling #ulse
C. Increase the sam#ling #ulse ?. ?ecrease the ste# si/e=
5F. 7it rate refers to the rate of change of a !igital information signal+ which is
usually inary. 7au!+ like it rate+ is also a rate of change, howe$er+ au! refers to the rate of change of a signal on the transmission me!ium after enco!ing an! mo!ulation ha$e occurre!. 6ence+ au! is a unit of transmission rate+ mo!ulation rate+ or symol rate. If the transmitter sen!s
C. 3
>B. ; ty#e of locking co!ing scheme !esigne! to e use! in comination with NRI.
0rolem with synchroni/ation in NRI can e minimi/e! y changing the it stream+ #rior to enco!ing with NRI+ so that it !oes not ha$e long stream of Bs. ;. 478<7 =
7. @783B7 C. <7847 ?. 3B78@7 multi#le"ing (T?M* is a !igital #rocess that allows se$eral connections to share the high an!wi!th of a link. T?M is a !igital multi#le"ing technique for comining se$eral lowrate channels into one highrate one. 'e can !i$i!e T?M into two !ifferent schemes: synchronous or statistical. ?ifferentiate the two ty#es of T?M
>3. Time!i$ision
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;. In synchronous T?M+ each in#ut connection has an allotment in the out#ut e$en if
it is not sen!ing !ata while in statistical T?M+ slots are !ynamically allocate! to im#ro$e an!wi!th efficiency. = 7. In statistical T?M+ each in#ut connection has an allotment in the out#ut e$en if it is not sen!ing !ata while in synchronous T?M+ slots are !ynamically allocate! to im#ro$e an!wi!th efficiency. C. ; statistical T?M has a finite numer of highs#ee! !ata in#ut lines with one highs#ee! multi#le"e! !ata out#ut line+ an! each in#ut line has its own !igital enco!er an! uffer while synchronous T?M often contains an aun!ance of time slots within each frame that contain no information. ?. ; synchronous T?M has a finite numer of highs#ee! !ata in#ut lines with one highs#ee! multi#le"e! !ata out#ut line+ an! each in#ut line has its own !igital enco!er an! uffer while statistical T?M often contains an aun!ance of time slots within each frame that contain no information. >%. Su##ose
you are gi$en a task y your oss to analy/e a s#ecific microwa$e communication system. ;n AM POS microwa$e link o#erates at 5.3< 96/. The require! recei$er IA an!wi!th is %B M6/ The transmitter out#ut #ower is 2B !7m. The recei$er front en!s first acti$e stage is a mi"er with a noise figure of F !7. The #ath length is %3 mi, the antennas at each en! ha$e a 2<!7 gain an! the transmission line losses at each en! are 2 !7. IA the im#ro$ement threshol! is use! as the unfa!e! reference+ what is the reliaility of the ra!io link ;. [email protected]
7. F@.
C. FF.F@%V =
?. [email protected]%FV
>2. Crosstalk can e !efine! as any !isturance create! in a communications channel y
signals in other communications channels. It is a #otential #rolem whene$er two metallic con!uctors carrying !ifferent signals are locate! in close #ro"imity to each other. Using the conce#t of crosstalk+ what is the !ifference etween nonlinear crosstalk an! transmittance crosstalk ;. Nonlinear crosstalk is a !irect result of nonlinear am#lification (hence the name* in analog communications systems. Nonlinear am#lification #ro!uces harmonics an! cross #ro!ucts (sum an! !ifference frequencies* while transmittance crosstalk is most #re$alent when filters !o not a!equately reHect un!esire! #ro!ucts from other channels. 7ecause this ty#e of interference is cause! y ina!equate control of the transfer characteristics or transmittance of networks.= 7. Nonlinear crosstalk is most #re$alent when filters !o not a!equately reHect un!esire! #ro!ucts from other channels. 7ecause this ty#e of interference is cause! y ina!equate control of the transfer characteristics or transmittance of networks while transmittance crosstalk is a !irect result of nonlinear am#lification (hence the name* in analog communications systems. Nonlinear am#lification #ro!uces harmonics an! cross #ro!ucts (sum an! !ifference frequencies*. C. Nonlinear crosstalk is !ue to the effects of nearfiel! mutual in!uction etween cales from #hysically isolate! circuits. To re!uce nonlinear crosstalk !ue to mutual in!uction+ wires are twiste! together (hence the name twiste! #air* while Transmittance Crosstalk is a !irect result of nonlinear am#lification (hence the name* in analog communications systems. Nonlinear am#lification #ro!uces harmonics an! cross #ro!ucts (sum an! !ifference frequencies* ?. Nonlinear crosstalk is a !irect result of nonlinear am#lification (hence the name* in analog communications systems. Nonlinear am#lification #ro!uces harmonics an! cross #ro!ucts (sum an! !ifference frequencies*while Transmittance Crosstalk is !ue to the effects of nearfiel! mutual in!uction etween cales from #hysically isolate! circuits. To re!uce nonlinear crosstalk !ue to mutual in!uction+ wires are twiste! together (hence the name twiste! #air* >4. In am#litu!e mo!ulation+ the information signal $aries the am#litu!e of the carrier
sine wa$e. The instantaneous $alue of the carrier am#litu!e changes in accor!ance with the am#litu!e an! frequency $ariations of the mo!ulating signal. 'hich is not true aout am#litu!e mo!ulation ;. The re#etition rate of the en$elo#e of the ;M wa$e is equal to the frequency of the mo!ulating signal. 7. ;M wa$e has its ma"imum $alue at the #ositi$e #eak of the mo!ulating signal an! minimum $alue at the negati$e #eak. C. The out#ut of the mo!ulator is the carrier signal when the mo!ulating signal is not #resent.
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?. 'hen the mo!ulating signal am#litu!e is greater than the carrier signal am#litu!e+ crosso$er !istortion occurs which is a result of o$ermo!ulation.= ><. Aor the gi$en #arameters+ !etermine the energy #er itto noise #ower !ensity ratio
C 1 3B3% '+ f 1 5B k#s+ N 1 3.% " 3B 34 '+ 7 1 3%B k6/ ;. %5.4 !7
7. 3<.2 !7
C. %%.% !7=
?. 22.> !7
>5. ?elta
mo!ulation uses a singleit 0CM co!e to achie$e !igital transmission of analog signals. Rather than transmit a co!e! re#resentation of the sam#le+ only a single it is transmitte!+ which sim#ly in!icates whether that sam#le is larger or smaller than the #re$ious sam#le. If the slo#e of the analog signal is greater than the !elta mo!ulator can maintain+ slo#e o$erloa! results. 'hich of the following is not a way to re!uce slo#e o$erloa! ;. Increasing the ste# si/e while using the same sam#ling frequency will re!uce the slo#e o$erloa!. 7. Increasing the sam#ling frequency for the same ste# si/e will re!uce slo#e o$erloa!. C. ;!a#ti$e !elta mo!ulation can e use! to re!uce slo#e o$erloa!. ?. ; limiter is use! to remo$e the e"cess $oltage #ro!uce! y slo#e o$erloa!.=
>>. 'hat
is the line enco!ing use! in a Stan!ar! &thernet Im#lementation Z3B7ase<+ 3B7ase%+ 3B7aseT 3B7aseA[ ;. MPT2
7. NRI
C. Manchester=
?. 4?0;M
>@. Com#an!ing is the #rocess of com#ressing an! then e"#an!ing. 'ith com#an!e! systems+
the higheram#litu!e analog signals are com#resse! (am#lifie! less than the lower am#litu!e signals* #rior to transmission an! then e"#an!e! (am#lifie! more than the loweram#litu!e signals* in the recei$er. The following !escries the effect of com#an!ing e"ce#t ;. Com#an!ing is a means of im#ro$ing the !ynamic range of a communications system. 7. Com#an!ing !ecreases quanti/ation error without the nee! to increase the numer of le$els require! for quanti/ation. C. Com#an!ing im#ro$es synchroni/ation y using clock reco$ery.= ?. Com#an!ing im#ro$es the signaltoquanti/ation noise ratio. >F. In this enco!ing metho!+ the !uration of the it is !i$i!e! into two hal$es. The
$oltage remains at one le$el !uring the first half an! mo$es to the other le$el in the secon! half. The transition at the mi!!le of the it #ro$i!es synchroni/ation. ;. 7@S
7. Manchester
=
C. ;MI
?. #seu!otenary
@B. Aa!ing can e minimi/e! y using what is calle! a !i$ersity system. ; !i$ersity
system uses multi#le transmitters+ recei$ers+ or antennas to mitigate the #rolems cause! y multi#ath signals. 'hat ty#e of !i$ersity system uses two recei$er antennas s#ace! as far a#art as #ossile to recei$e the signals This !i$ersity system is use! mainly at ase stations rather than in #ortale or han!hel! units. The asic i!ea is that antennas at slightly !ifferent locations will recei$e !ifferent $ariations of the signals+ with one eing etter than the other. ;. Arequency !i$ersity 7. 0olari/ation !i$ersity
C. S#atial !i$ersity= ?. Recei$er !i$ersity
@3. It is the OSI layer res#onsile for network a$ailaility (i.e.+ !ata storage an!
#rocessor ca#acity*. Its #rotocols #ro$i!e the logical connection entities at the a##lication layer. These a##lications inclu!e file transfer #rotocols an! sen!ing e mail. Its res#onsiilities inclu!e network logon an! logoff #roce!ures an! user authentication. It !etermines the ty#e of !ialogue a$ailale (i.e.+ sim#le"+ half !u#le"+ or full !u#le"*. Its characteristics inclu!e $irtual connections etween a##lications entities+ synchroni/ation of !ata flow for reco$ery #ur#oses+ creation of !ialogue units an! acti$ity units+ connection #arameter negotiation+ an! #artitioning ser$ices into functional grou#s. ;. ;##lication layer 7. Trans#ort layer @%. 0haseshift
C. Session layer= ?. 0resentation layer
keying (0S* is another form of anglemo!ulate!+ constantam#litu!e !igital mo!ulation. 0S is an Mary !igital mo!ulation scheme similar to con$entional #hase mo!ulation e"ce#t with 0S the in#ut is a inary !igital signal an! there are a limite! numer of out#ut #hases #ossile. The in#ut inary information is enco!e! into grou#s of its efore mo!ulating the carrier. Its
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$ariations inclu!e 70S+ X0S+ @0S+ 350S among others. 'hich is the a!$antage of X0S in terms of an!wi!th an! noise immunities
maHor
;. The an!wi!th require! for X0S is half than 0S with similar noise immunities= 7. The an!wi!th require! for X0S is twice than 0S with similar noise immunities C. The an!wi!th require! for X0S is one thir! than 0S with !ifferent noise immunities ?. The an!wi!th require! for X0S is !oule than 0S with either same or !ifferent noise immunities !e#en!ing on the transmission rate @2. The an!wi!th of a $i!eo signal is 4.< M6/. This signal is to e transmitte! using
0CM with the numer of quanti/ation le$els X 1 3B%4. The sam#ling rate shoul! e %BV higher than the Nyquist rate. Calculate the system it rate. ;. F.%35 9#s
7. 33.B
C. FB M#s
?. 3B@ M#s=
@4. ; line of sight ra!io link is to e uilt in 7aguio+ o#erating at a frequency of
596/ has a se#aration of 4Bkm etween antennas. ;n ostacle+ 3B m high+ in the #ath is locate! 3Bkm form the transmitting antenna. 7y how much must the eam clear the ostacle ;. 3F.2 m
7. 33.5 m
C. %3.5 m=
?. %F.2 m
@<. ;n o#tic fier is ma!e of glass with a refracti$e in!e" of 3.<< an! is cla! with
another glass with a refracti$e in!e" of 3.<3. Paunching takes #lace from air. 'hat numerical a#erture !oes the fier ha$e ;. B.32%
7. B.2<%=
C. B.B2%
?. B.4><
@5. The ratio of the mo!ulating signal am#litu!e to the carrier signal am#litu!e is
calle! the mo!ulation in!e"+ the i!eal $alue of which is 3. 'hen mo!ulation in!e" is greater than 3 which means that the mo!ulating signal am#litu!e is greater than the carrier signal am#litu!e+ o$ermo!ulation occurs. 'hich is not a result of o$ermo!ulation ;. The an!wi!th of the resulting signal is greater ecause of the harmonics create! !ue to o$ermo!ulation. 7. Some #art of the signal is cli##e!+ thus information ecomes unintelligile. C. O$ermo!ulation causes the local oscillator to !rift from its center frequency.= ?. ?istortion cause! y o$ermo!ulation #ro!uces a!Hacent channel interference. @>. ; sensiti$e an! selecti$e recei$er can
e ma!e using only am#lifiers+ selecti$e filters+ an! a !emo!ulator. This is calle! a tune! ra!io frequency or TRA recei$er. &arly ra!ios use! this !esign. 6owe$er+ such a recei$er !oes not usually !eli$er the kin! of #erformance e"#ecte! in mo!ern communications a##lications. One ty#e of recei$er that can #ro$i!e that #erformance is the su#erhetero!yne recei$er. Su#erhetero!yne recei$ers con$ert all incoming signals to a lower frequency+ known as the interme!iate frequency (IA*+ at which a single set of am#lifiers an! filters is use! to #ro$i!e a fi"e! le$el of sensiti$ity an! selecti$ity. 'hich is not an a!$antage of su#erhetero!yne o$er the TRA !esign ;. Su#erhetero!yne has su#erior gain since it uses ;9C which automatically a!Husts the gain !e#en!ing on the le$el of the recei$e! signal. 7. It is more stale ecause it has lesser numer of am#lifiers to e tune! to the same center frequency. C. The recei$er is more selecti$e ecause it only nee!s to acce#t signals with frequencies equal to the Interme!iate Arequency. ?. The local oscillator is less likely to !rift for a su#erhetero!yne recei$er than for the TRA !esign.=
@@. ; 3 m' $i!eo signal ha$ing a an!wi!th of 3BB M6/ is transmitte! to a recei$er
through cale that has 4B !7 loss. If the effecti$e onesi!e noise s#ectral !ensity at the recei$er is 3B %B 'att86/+ then the signaltonoise ratio at the recei$er is ;.
7. 2B !7
C. 4B !7
?. 5B !7
@F. ?etermine the 6amming !istance for the co!ewor!s (3B3B3+ 33BB3*
;. one
7. two=
C. three
?. four
FB. 'hich of the
following statements est !escrie the #ur#ose for the use of an antenna cou#ler ;. It allows the transmitter to e o#erate! at more than one carrier frequency at the same time. 7. It allows the transmitter to e connecte! to se$eral antennas at the same time.
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C. It is use! to filter out the carrier frequency from the transmitters ;M out#ut signal. ?. It is use! to match the out#ut im#e!ance of the transmitter with the in#ut im#e!ance of the antenna to ensure ma"imum #ower transfer.= F3. 0ulse !ialing is a signaling technology in telecommunications in which a !irect current local loo# circuit is interru#te! accor!ing to a !efine! co!ing system for each signal transmitte!+ usually a !igit. 6ow long !oes it take to !ial the numer >@42>4< using #ulse !ialing with ..B s F%. In fier o#tics terminology+ the wor! mo!e sim#ly means #ath. If there is only one #ath for light rays to take !own a cale+ it is calle! single mo!e. If there is more than one #ath+ it is calle! multimo!e. 'hich of the following refers to a characteristic of a multimo!e fier o#tic ;. Cla!!ing thickness is greater than the ra!ius of the core an! the !iameter of the core must e much greater than the wa$elength of the light to e carrie!.= 7. Cla!!ing thickness is less than the ra!ius of the core an! !iameter of the core must e greater than the wa$elength of the light to e carrie!. C. Cla!!ing thickness is greater than the ra!ius of the core an! the !iameter of the core must e lesser than the wa$elength of the light to e carrie!. ?. Cla!!ing thickness is less than the ra!ius of the core an! the !iameter of the core must e lesser than the wa$elength of the light to e carrie!. F2. ;ny circuit that will con$ert a frequency $ariation in the carrier ack to a #ro#ortional $oltage $ariation can e use! to !emo!ulate or !etect AM signals. Circuits use! to reco$er the original mo!ulating signal from an AM transmission are calle! !emo!ulators+ !etectors+ or !iscriminators. ;n AM recei$er rarely works satisfactorily without an RA am#lifier ecause ;. AM recei$ers ty#ically work with smaller in#ut signal le$els !ue to their noise characteristics= 7. AM recei$ers ha$e a narrower an!wi!th. C. AM recei$ers !o not ha$e $ery much gain in their IA am#lifier stages. ?. AM recei$ers nee! RA am#lifier stages to e ale to !eco!e stereo signals. F4. ; half wa$e !i#ole with a gain of %.34 !7i is fe!+ y means of lossless+ matche! line y a %< watts transmitter. 'hat is the electric fiel! strength of the signal measure! 3< km from the antenna in free s#ace in the !irection of ma"imum ra!iation ;. %.24 mD8m= 7. <.%2 mD8m C. 4.<5 mD8m ?. 4<.%5 mD8m F<. Image frequency is any frequency other than the selecte! ra!io frequency carrier that+ if allowe! to enter a recei$er an! mi" with local oscillator will #ro!uce a cross#ro!uct frequency that is equal to interme!iate frequency. Thus+ it is !esirale that the recei$er shoul! e ale to reHect image frequencies as it mi"es with the !esire! signal. AM is less likely to encounter #rolems with image frequencies than ;M. 'hy are image frequencies somewhat less of a #rolem in AM recei$ers than they are in SS7 or ;M recei$ers ;. Single si!ean! systems use less an!wi!th than AM. Narrowan! signals are more likely to e affecte! y image frequencies. 7. If it recei$es two signals with the same frequency+ it only !emo!ulates the signal with the higher #ower. This is known as ca#ture effect.= C. AM mi"er stages are squarelaw !e$ices. Secon! harmonic is eliminate! which is the main source of image frequency. ?. AM recei$ers !o not use the su#erhetero!yne !esign. The su#erhetero!yne !esign is more likely to create image frequency. F5. 'hether !igital signals are eing transmitte! y asean! metho!s or roa!an! metho!s+ efore the !ata is #ut on the me!ium+ it is usually enco!e! in some way to make it com#atile with the me!ium or to facilitate some !esire! o#eration connecte! with the transmission. One of the enco!ing techniques is the Return to ero or R. In return to /ero (R* enco!ing+ the $oltage le$el assigne! to a inary 3 le$el returns to /ero !uring the it #erio!. 'hich of the following is not a common R co!e ;. Runi#olar 7. Ri#olar C. RM= ?. R;MI F>. 6ow a light ray reacts when it meets the interface of two transmissi$e materials that ha$e !ifferent in!e"es of refraction can e e"#laine! with Snells law. The angle of inci!ence is the angle at which the #ro#agating ray strikes the interface with res#ect to the normal+ an! the angle of refraction is the angle forme! etween the #ro#agating ray an! the normal after the ray has entere! the secon! me!ium.
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'hich of the following will not ha##en when light tra$els from one me!ium to another me!ium with a !ifferent refracti$e in!e" ;. If the first me!ium has a lower in!e" of refraction than the secon!+ light will e refracte! towar!s the normal line. 7. If the first me!ium has a lower in!e" of refraction than the secon! an! the angle of inci!ence is equal to the critical angle+ light will tra$el along the oun!ary.= C. If the first me!ium has a higher in!e" of refraction than the secon!+ light will e refracte! away from the normal line. ?. If the first me!ium has a higher in!e" of refraction than the secon!+ it is #ossile that light will e reflecte!. F@. ;n earth station for use with a geostationary satellite has a !ish antenna which
sees a sky tem#erature of %< . It is connecte! to the recei$er with a fee!line ha$ing 3 !7 loss. The recei$er equi$alent noise tem#erature is 3< . Calculate the noise tem#erature for the system. ;. F< =
7. @B
C. 4<
?. 33<
FF. The antenna is the interface etween the transmission line an! s#ace. ;ntennas are
#assi$e !e$ices, the #ower ra!iate! cannot e greater than the #ower entering from the transmitter. In other wor!s+ antenna cannot am#lify signals. 6owe$er+ some antennas can recei$e higher signal le$els than others ecause of higher gain. 'hat+ then+ is meant y antenna gain ;. The final am#lifier gain minus the transmission line losses (inclu!ing any #hasing lines #resent* 7. The ratio of the amount of #ower #ro!uce! y the antenna com#are! to the out#ut #ower of the transmitter C. The ratio of the signal in the ackwar! !irection ?. The numeric ratio relating the ra!iate! signal strength of an antenna to that of another antenna= 3BB. Su##ose you ha! an AM signal with a carrier of 3B M6/ an! a !e$iation of 3B k6/.
'hich of the following est e"#lain how you coul! use it to get an AM signal M6/ with a !e$iation of %B k6/. ;. Airst+ #ut the signal through a frequency !ouler to get a %BM6/ carrier 3Bk6/ !e$iation. Then mi" that signal with a 3
NOT6IN9 AOPPO'S
at 3BB with a a 3BB with a a 3BB with a a 3BB with a a 3BB