Preboard.EST.2ndBatch.April2015.SetB.doc

Republic of the Philippines Professional Regula tion Co mmission Board of Electronics Engineering

ECE Licensure Examination – Pre-Board Exam

1:00 pm – :00 pm

Page 1 of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

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!emo!ul am#litu!emo!ulate! ate! $i!eo signal signal an! frequencym frequencymo!ulate! o!ulate! au!io au!io signal= signal= Two am#litu!e am#litu!emo!ulate mo!ulate! ! signals: signals: $i!eo $i!eo an! an! au!io ;n am#litu!emo!ul am#litu!emo!ulate! ate! au!io signal signal an! frequencym frequencymo!ulate! o!ulate! $i!eo $i!eo signal Two frequency frequencymo!ulate mo!ulate! ! signals: signals: $i!eo $i!eo an! an! au!io

<. One kilowatt is su##lie! to a rhomic 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$ing station+ a halfwa$e antenna+ #ro#erly oriente! an! locate! near the rhomic+ must e su##lie! with 35.5 k'. 'hat is the gain of the rhomic ;. 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 ao$ ao$e. e. >. The squarelaw 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 crossmo crossmo!ula !ulation tion= =

electrical length of stan!ar! stan!ar! R9@8U coa"ial cale woul! e require! to otain @. 'hat electrical a 4


1:00 pm – :00 pm

Page / of 1.

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 #roale. 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 storean!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#ailities. 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. GHocot(Jl*

C.B

?.

GHotan(Jl* =

3%. Network to#ology !escries the layout or a##earance of a networkKthat is+ how the

com#uters+ cales+ 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!ingwa$e ratio (S'R* is a mathematical e"#ression of the nonuniformity of an

electromagnetic fiel! (&M fiel!* on a transmission line such as coa"ial cale. Usually+ S'R is !efine! as the ratio of the ma"imum ra!iofrequency ( 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!ingwa$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 !escries 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 aout 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<. ?ualtone multifrequency (?TMA* is a sim#le twoofeight 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 numers from a suscriers location to the central office switching machine. Its main a!$antage is s#ee! an! control. It was originally calle! TouchTone. Su##ose you #ress F+ this will e equi$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 !irectsequence s#rea! s#ectrum (?SSS* co!e+ such as a 0seu!o

ran!om Noise (0N* co!e sequence use! in !irectsequence co!e !i$ision multi#le access (C?M;* channel access techniques



1:00 pm – :00 pm

Page  of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

;. flake 7. it C. nile ?. 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 #ulic !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 $ariale si/e ;. Only #ackets of a fi"e! si/e are com#atile for #arallel transmission. 0ackets of $ariale si/e are com#atile 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 $ariale si/e nee! start an! sto# its while #ackets of fi"e! si/e !ont. ?. None of these. 7oth #ackets of $ariale 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 quarterwa$elength. Aor a lossless 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 $ersa+ !e#en!ing on whether the line is terminate! in a short or an o#en. 'hich of the following statements is false regar!ing transmission line ;. ; quarterwa$elength+ short circuite! transmission line has ma"imum im#e!ance. 7. ; halfwa$elength+ o#en circuite! transmission line has ma"imum im#e!ance. C. ; transmission line less than one quarterwa$elength long an! short circuite! will a##ear ca#aciti$e.= ?. ; transmission line more than one halfwa$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 freeruns 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$e in!ices. It is also require! that the inci!ent angle e less than the critical angle for total internal refraction to occur. 'hat is meant y critical angle ;. Critical angle is the angle at which light is refracte!. 7. Critical angle is the angle at which light ecomes in$isile. 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 aout < cm elow groun! 7. a large numer of ra!ials e"ten!ing from ase of tower at a !e#th of aout 2 m C. a large numer of ra!ials e"ten!ing from ase of tower at a !e#th of aout 2B cm = ?. none of the ao$e %4. Aor

an o#tical !etermine the transmissions.

fier 3B ma"imum

km long !igital

with a #ulses#rea!ing constant of < ns8km+ transmission rates for Nonreturnto/ero



1:00 pm – :00 pm

Page  of 1.

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 nonresonant antenna

;. Aol!e! !i#ole

7. 7roa! si!e array

C. &n! fire array

?. Rhomic 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 onehalf 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#lers laws can e a##lie! to any two o!ies in s#ace that interact through gra$itation. The larger of the two o!ies is calle! the #rimary an! the smaller is calle! the secon!ary or satellite. e#lers secon! law is known as the Paw of ;reas. It states that for equal inter$als of time+ a satellite will swee# out equal areas in the orital #lane+ focuse! at the arycenter (the center of mass of the #rimary*. 'hat conclusion can e !rawn from e#lers 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#lers 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$oi!e!. ?. None of these. CSM;8C? #ackets !ont ha$e a minimum

a cale coul! get on+ sen! a far enough to colli!e. The a cale coul! not get on as a cale coul! get on+ sen! a far enough to colli!e. The si/e limit.

%F. ; #ointto#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 cale 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$ereration

time

;. Saine &quation 7. Ste#hens  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 !7S0P =

C. >F !7S0P

?. 5F !7S0P

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



1:00 pm – :00 pm

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

Page . of 1. %E! B

22. There

are two !e$ices commonly use! to !etect light energy in fiero#tic communications recei$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$elength or frequency. 7. )ar5 current4 The leakage current that flows through a #hoto!io!e with no light in#ut. Thermally generate! carriers in the !io!e cause !ark current. C. !ransit time4 The time it takes a lightin!uce! carrier to tra$el across the !e#letion region of a semicon!uctor. This #arameter !etermines the ma"imum it rate #ossile with a #articular #hoto!io!e. ?. Light sensiti2it34 The ma"imum o#tical #ower a light !etector can recei$e an! still #ro!uce a usale electrical out#ut signal. Pight sensiti$ity is generally gi$en for a #articular wa$elength in either !7m or !7. =

24. Su##ose there is an ostacle 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

numer 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 0reem#hasis an! ?eem#hasis in AM 7roa!casting

;. 0reem#hasis is increasing the relati$e strength of lowfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is !ecreasing the relati$e strength of lowfrequency com#onents of the out#ut signal of an AM !etector in an AM recei$er. 7. 0reem#hasis is !ecreasing the relati$e strength of lowfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is increasing the relati$e strength of lowfrequency com#onents of the out#ut signal of an AM !etector in an AM recei$er. C. 0reem#hasis is !ecreasing the relati$e strength of highfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is increasing the relati$e strength of highfrequency com#onents at the out#ut signal of an AM !etector in an AM recei$er. ?. 0reem#hasis is increasing the relati$e strength of highfrequency com#onents efore eing fe! into the mo!ulator of an AM transmitter while !eem#hasis is !ecreasing the relati$e strength of highfrequency com#onents at the out#ut signal of an AM !etector in an AM recei$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!ean! 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 estalishe! etween &nglan! an! Unite! States. One common !esignation assigne! y International Telecommunication Union (ITU* is C2A !esignation. ?escrie 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 !oule si!ean! transmission in which the transmitter consists of two in!e#en!ent singlesi!ean! su##resse! carrier mo!ulators.



1:00 pm – :00 pm

Page  of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

7. (' 8estigial %ideband4 It is a form of am#litu!e mo!ulation in which the carrier an! once com#lete si!ean! are transmitte!+ ut only #art of the secon! si!ean! 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 selectale* 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! IS325 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 Mau! = 7. 7'1@B M6/+ au! rate1 %B Mau!

C. 7'1>B M6/+ au! rate1 %B Mau! ?. 7'15B M6/+ au! rate1 2B Mau!

4%. The half wa$e !i#ole is forme! from a con!ucting element which is wire or metal tue

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#ale 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. 9reuenc3-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.


ECE Licensure Examination – Pre-Board Exam ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

1:00 pm – :00 pm

Page < of 1. %E! B

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$e as a structural gui!eline for e"changing information etween com#uters+ workstations+ an! networks. In the OSI layer+ what is the #ur#ose of session layer ;. The layer is res#onsile for network a$ailaility (i.e.+ !ata storage an! #rocessor ca#acity*. This #rotocol #ro$i!es the logical connection entities at the a##lication layer. These a##lications inclu!e file transfer #rotocols an! sen!ing email. The res#onsiilities inclu!e network logon an! logoff #roce!ures an! user authentication. = 7. It is res#onsile for #ro$i!ing errorfree communications across the #hysical link connecting #rimary an! secon!ary stations (no!es* within a network (sometimes referre! to as ho#toho# !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$i!es !etails that enale !ata to e route! etween !e$ices in an en$ironment using multi#le networks+ sunetworks+ or oth. Com#onents that o#erate at this layer inclu!e routers an! their software. It !etermines which network configuration is most a##ro#riate for the function #ro$i!e! y the network an! a!!resses an! routes !ata within networks y estalishing+ 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 $oltage sam#le+ the it rate is aout ;. 3.F k its8sec = 7. B.F< k its8sec C. 2.@ k its8sec ?. >.5 k its8sec 4>. 7an!wi!th utili/ation is the wise use of a$ailale 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 highit rate information signal to generate a low it rate #seu!oran!om signal closely resemling 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



1:00 pm – :00 pm

Page = of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

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 highit rate information signal to generate a low it rate #seu!oran!om signal closely resemling 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$e as a structural gui!eline for e"changing information etween com#uters+ workstations+ an! networks. In the OSI layer+ what is the #ur#ose of network layer ;. It is res#onsile for #ro$i!ing errorfree 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#onsile for network a$ailaility (i.e.+ !ata storage an! #rocessor ca#acity*. This #rotocol #ro$i!es the logical connection entities at the a##lication layer. These a##lications inclu!e file transfer #rotocols an! sen!ing email. The res#onsiilities inclu!e network logon an! logoff #roce!ures an! user authentication. C. It #ro$i!es !etails that enale !ata to e route! etween !e$ices in an en$ironment using multi#le networks+ sunetworks+ or oth. Com#onents that o#erate at this layer inclu!e routers an! their software. It !etermines which network configuration is most a##ro#riate for the function #ro$i!e! y the network an! a!!resses an! routes !ata within networks y estalishing+ 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 suscriers 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 lines 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.



1:00 pm – :00 pm

Page > of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

7. 7oth AM an! 0M a##ear to e frequency mo!ulate! signal C. 0M carrier a##ears to e frequencymo!ulate! y signal while AM a##ears to e frequencymo!ulate! signal = ?. AM carrier a##ears to e frequencymo!ulate! y signal while 0M a##ears to e frequencymo!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 !oule!. The ma"imum range will

;. e !oule! = 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 #ulic roa!cast system+

it shoul! transmit using ;. 7. C. ?.

#araolic 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 aility of the recei$er to acce#t a gi$en an! of frequencies an! reHect all others. There are se$eral ways to !escrie the selecti$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$e only #art of the an!wi!th of the ;M signal is am#lifie!+ causing some of the si!ean! information to e lost an! !istortion results while un!erselecti$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!ean! 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



1:00 pm – :00 pm

Page 10 of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

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$e insulator (!ielectric*+ such as #air of wires or system of wire #airs. 'hen o is not equal to  P+ some of inci!ent #ower is asore! y the loa! an! some is reflecte! to the source. This is calle! unmatche! or mismatche! lines. ; nonlossy transmission line terminate! with an o#en circuit will ha$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 numer 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. NRP ?. 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 numer of #ossiilities to a

finite numer of con!itions. ;nalog signals contain an infinite numer of am#litu!e #ossiilities. Thus+ con$erting an analog signal to a 0CM co!e with a limite! numer of cominations requires quanti/ation. In essence+ quanti/ation is the #rocess of roun!ing off the am#litu!es of flatto# sam#les to a manageale numer of le$els. The !ecimal $alue a!!e! to or sutracte! from the original $alue is consi!ere! an error an! is calle! quanti/ation error. 'hich of the following !ecreases quanti/ation error ;. ?ecrease the numer of le$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 symol rate. If the transmitter sen!s
C. 3
>B. ; ty#e of locking co!ing scheme !esigne! to e use! in comination with NRI.

0rolem with synchroni/ation in NRI can e minimi/e! y changing the it stream+ #rior to enco!ing with NRI+ 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$eral connections to share the high an!wi!th of a link. T?M is a !igital multi#le"ing technique for comining se$eral lowrate channels into one highrate 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



1:00 pm – :00 pm

Page 11 of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

;. 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 numer of highs#ee! !ata in#ut lines with one highs#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 aun!ance of time slots within each frame that contain no information. ?. ; synchronous T?M has a finite numer of highs#ee! !ata in#ut lines with one highs#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 aun!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 reliaility of the ra!io link ;. [email protected]
7. F@.
C. FF.F@%V =

?. [email protected]%FV

>2. Crosstalk can e !efine! as any !isturance create! in a communications channel y

signals in other communications channels. It is a #otential #rolem 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 nearfiel! mutual in!uction etween cales 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 nearfiel! mutual in!uction etween cales 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 $ariations of the mo!ulating signal. 'hich is not true aout am#litu!e mo!ulation ;. The re#etition rate of the en$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.



1:00 pm – :00 pm

Page 1/ of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

?. '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 itto noise #ower !ensity ratio

C 1 3B3% '+ 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 singleit 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%+ 3B7aseT  3B7aseA[ ;. MPT2

7. NRI

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 higheram#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 loweram#litu!e signals* in the recei$er. The following !escries the effect of com#an!ing e"ce#t ;. Com#an!ing is a means of im#ro$ing the !ynamic range of a communications system. 7. Com#an!ing !ecreases quanti/ation error without the nee! to increase the numer 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 signaltoquanti/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$ers+ or antennas to mitigate the #rolems cause! y multi#ath signals. 'hat ty#e of !i$ersity system uses two recei$er antennas s#ace! as far a#art as #ossile to recei$e the signals This !i$ersity system is use! mainly at ase stations rather than in #ortale or han!hel! units. The asic i!ea is that antennas at slightly !ifferent locations will recei$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#onsile for network a$ailaility (i.e.+ !ata storage an!

#rocessor ca#acity*. Its #rotocols #ro$i!e the logical connection entities at the a##lication layer. These a##lications inclu!e file transfer #rotocols an! sen!ing e mail. Its res#onsiilities inclu!e network logon an! logoff #roce!ures an! user authentication. It !etermines the ty#e of !ialogue a$ailale (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 @%. 0haseshift

C. Session layer= ?. 0resentation layer

keying (0S* is another form of anglemo!ulate!+ constantam#litu!e !igital mo!ulation. 0S is an Mary !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! numer of out#ut #hases #ossile. The in#ut inary information is enco!e! into grou#s of its efore mo!ulating the carrier. Its



1:00 pm – :00 pm

Page 1 of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

$ariations inclu!e 70S+ X0S+ @0S+ 350S among others. 'hich is the a!$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 !oule 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 numer 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 ostacle+ 3B m high+ in the #ath is locate! 3Bkm form the transmitting antenna. 7y how much must the eam clear the ostacle ;. 3F.2 m

7. 33.5 m

C. %3.5 m=

?. %F.2 m

@<. ;n o#tic fier is ma!e of glass with a refracti$e in!e" of 3.<< an! is cla! with

another glass with a refracti$e in!e" of 3.<3. Paunching takes #lace from air. 'hat numerical a#erture !oes the fier ha$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 unintelligile. 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 stale ecause it has lesser numer 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 cale that has 4B !7 loss. If the effecti$e onesi!e noise s#ectral !ensity at the recei$er is 3B %B 'att86/+ then the signaltonoise 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 !escrie 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.


ECE Licensure Examination – Pre-Board Exam ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

1:00 pm – :00 pm

Page 1 of 1. %E! B

C. It is use! to filter out the carrier frequency from the transmitters ;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 numer >@42>4< using #ulse !ialing with ..B s F%. In fier o#tics terminology+ the wor! mo!e sim#ly means #ath. If there is only one #ath for light rays to take !own a cale+ 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 fier 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 ale 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 !esirale that the recei$er shoul! e ale to reHect image frequencies as it mi"es with the !esire! signal. AM is less likely to encounter #rolems with image frequencies than ;M. 'hy are image frequencies somewhat less of a #rolem in AM recei$ers than they are in SS7 or ;M recei$ers ;. Single si!ean! systems use less an!wi!th than AM. Narrowan! signals are more likely to e affecte! y image frequencies. 7. If it recei$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 squarelaw !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 asean! 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#atile 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$el returns to /ero !uring the it #erio!. 'hich of the following is not a common R co!e ;. Runi#olar 7. Ri#olar C. RM= ?. R;MI F>. 6ow a light ray reacts when it meets the interface of two transmissi$e materials that ha$e !ifferent in!e"es of refraction can e e"#laine! with Snells 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.



1:00 pm – :00 pm

Page 1. of 1.

ELEC!R"#$C% %&%!E'% (#) !EC*#"L"+$E%

%E! B

'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 #ossile 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$iation of %B k6/. ;. Airst+ #ut the signal through a frequency !ouler to get a %BM6/ carrier 3Bk6/ !e$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

Preboard.EST.2ndBatch.April2015.SetB.doc

Recommend Documents