Answer Keys for Electronics Communication Systems by George Kennedy.pdf

+. Indicate the   started as early as

KENNEDY 4 th EDITION true statement. %he process of sending and receiving MULTIPLE CHOICES

INTRO TO COMMUNICATIONS SYSTEM

a. the middle 13(s  b. 1-!( 1. Inc.athe communications system, noisecentury is most likely to affect the signal beginning of the twentieth . the ,-4" a. at the transmitter  b. in the channel -. hich of the steps is not included in the process of reception/ c. in the information source d. at the destination a. decoding b. enc$in) 2. Indicate the   c. storage wave of  d. consist interpretation

false

statement. Fourier analysis shows that a sawtooth

a. funa!ental anis"ubha#!$nic "ine . %he acoustic channel used for which of %a&e" the following/  b. a fundamental sine wave wave and an infinite number of harmonics c. fundamental and harmonic sine waves whose amplitude decreases with a. 0)F communications the harmonic number   b. single"sideband communication communication d. sinusoidal voltages, some of which are small enough to ignore in c. television communications  practice . 'e#"$n/t$/'e#"$n &$ice c$!!unicati$n"

3. the modulation   false statement. 1(.Indicate 'mplitude is the process of  Modulation is used to a. the ban%ith u"e a. #euce "u'e#i!'$"in) a l$% f#e0uenc( $n a hi)h f#e0uenc(  b. separate differing transmissions  b. superimposing a high high fre#uency on a low fre#uency c. ensure that intelligence may be transmitted over long distances c. carrier interruption d. the use ofand practicable antennas d. allow fre#uency shift phase shift

. Indicate the   false statement. From the transmitter the signal deterioration because of noise is usually a. unwanted energy b. '#eictable in cha#acte# c. present in the transmitter  d. due to any cause !. Indicate the

 

true statement. Most receivers conforms to the

a. amplitude"modulated group  b. fre#uency"modulated oup gr  c. "u'e#hete#$(ne )#$u' d. tuned radio fre#uency receiver group $. Indicate the   false e&emplified by the following.

statement. %he need for modulation can best be

a. Antenna len)th" %ill be a''#$*i!atel( +4 l$n)  b. 'n antenna in the the standard broadcast 'M 'M band is 1$,((( ft c. 'll sound is concentrated from 2( )* to 2( k)* d. ' message is composed of unpredictable variations in both amplitude and fre#uency

NOISE 1. ne of the following types of noise becomes of great importance at high fre#uencies. It is the a. shot noise  b. random noise c. impulse noise . t#an"it/ti!e n$i"e 2. Indicate the

 

false

statement.

a. )F mi&ers are generally noisier than )F amplifiers. b. I!'ul"e n$i"e &$lta)e i" ine'enent $f ban%ith. c. %hermal noise is independent of the fre#uency at which it is measured. d. Industrial noise is usually of the impulse type. 3. %he value of a resistor creating thermal noise is doubled. %he noise  power generator is therefore a. halved  b. #uadrupled c. doubled . unchan)e . ne of the following is  performance of receivers receivers

not  a useful #uantity for comparing the noise

a. In'ut n$i"e &$lta)e  b. #uivalent noise resistance resistance c. 4oise temperature d. 4oise figure

!. Indicate the noise whose source is in a category different from that of  the other three. a. 5olar noise  b. 6osmic noise c. At!$"'he#ic n$i"e d. 7alactic noise $. Indicate the   false statement. %he s#uare of the thermal noise voltage generated by a resistor is proportional to a. its resistance  b. its temperature c. 1$lt2!ann3" c$n"tant d. the bandwidth over which it is measured

NOISE 1. ne of the following types of noise becomes of great importance at high fre#uencies. It is the a. shot noise  b. random noise c. impulse noise . t#an"it/ti!e n$i"e 2. Indicate the

 

false

statement.

a. )F mi&ers are generally noisier than )F amplifiers. b. I!'ul"e n$i"e &$lta)e i" ine'enent $f ban%ith. c. %hermal noise is independent of the fre#uency at which it is measured. d. Industrial noise is usually of the impulse type. 3. %he value of a resistor creating thermal noise is doubled. %he noise  power generator is therefore a. halved  b. #uadrupled c. doubled . unchan)e . ne of the following is  performance of receivers receivers

not  a useful #uantity for comparing the noise

a. In'ut n$i"e &$lta)e  b. #uivalent noise resistance resistance c. 4oise temperature d. 4oise figure

!. Indicate the noise whose source is in a category different from that of  the other three. a. 5olar noise  b. 6osmic noise c. At!$"'he#ic n$i"e d. 7alactic noise $. Indicate the   false statement. %he s#uare of the thermal noise voltage generated by a resistor is proportional to a. its resistance  b. its temperature c. 1$lt2!ann3" c$n"tant d. the bandwidth over which it is measured

+. hich of broad classifications of noise are most difficult to treat/ a. n$i"e )ene#ate in the #ecei&e#  b. noise smitter  generated in the tran c. e*te#nall( )ene#ate n$i"e d. internally generated noise

-. 5pace noise generally covers a wide fre#uency spectrum, but the strongest interference occurs a. between - M)* and 1.3 7)*  b. below 2( Mh* c. bet%een  t$ , MH2 d. above 1.! 7)* . hen dealing with random noise calculations it must be remembered that a. all calculations are based on peak to peak values  b. calculations are based based on peak values c. calculations are based on average values . calculati$n" a#e ba"e $n RMS &alue" 1(. hich of the following is the most reliable measurement for comparing amplifier noise characteristics/ a. signal"to"noi se ratio b. n$i"e fact$# c. shot noise d. thermal noise agitation 11. hich of the following statements is

 

true /

a. 8andom noise power is inversely proportional to bandwidth  b. Flicker is sometimes sometimes called demodulation noise c. N$i"e i" !i*e#" i" cau"e b( inae0uate i!a)e f#e0uenc( #e5ecti$n d. ' random voltage across a resistance cannot be calculated

AMPLITUDE MODULATION 1. If the plate supply voltage for a plate"modulated class 6 amplifier is 9, the ma&imum plate"cathode voltage could be almost as high as a. 46  b. 39 c. 29 d. 19

2. In a low"level 'M system, amplifiers following the modulated stage must  be a. linea# e&ice"  b. harmonic devices c. class 6 amplifiers d. nonlinear devices

3. If the carrier of a 1(( percent modulated 'M wave is suppressed, the  percentage power saving will be a. !(  b. 1!( c. 1(( . 77.77 . :eak"type bias is used in a plate"modulated class 6 amplifier to a. prevent tuned circuit damping b. '#e&ent e*ce""i&e )#i cu##ent c. prevent overmodulation d. increase the bandwidth !. %he output stage of a television transmitter is most likely to be a a. plate"modulated class 6 amplifier  b. )#i/!$ulate cla"" C a!'lifie# c. screen"modulated class 6 amplifier  d. grid"modulated class ' amplifier  $. %he modulation inde& of an 'M wave is changed from ( to 1. %he transmitted power is a. unchanged  b. halved c. doubled . inc#ea"e b( 8 'e#cent

+. ne of the advantages of the base modulation over c ollector modulation of a transistor class 6 amplifier is a. the l$%e# !$ulatin) '$%e# #e0ui#e  b. higher power output output per transistor  c. better efficiency d. better linearity

-. ' carrier is simultaneously modulated by two sine waves with modulation indices of (.3 and (.; the total modulation inde& a. is 1  b. cannot be calculated unless unless the phase relations are known c. i" .8 d. is (.+ . 'mplitude modulation is used for broadcasting because a. it is more noise immune than other modulation systems.  b. 6ompared with other systems it re#uires less transmitting transmitting power  c. it" u"e a&$i" #ecei&e# c$!'le*it(. d. no other modulation system can provide the necessary bandwidth for  high fidelity 1(. hat is the ratio of modulating power to total power at 1(( percent modulation/ a. ,9:  b. 12 c. 23 d. 4one of the above

SIN;LE/SIDE1AND TECHNI" is connected to a coa&ial transmission line of E at 1( 7)*. %he   best  method of matching consists in connecting a. a short"circuited stub at the load  b. an inductance at the load c. a capacitance at some specific distance . a "h$#t/ci#cuite "tub at "$!e "'ecific i"tance f#$! the l$a 3. %he velocity factor of a transmission line a. e'en" $n the ielect#ic c$n"tant $f the !ate#ial u"e  b. increases the velocity along the transmission line c. is govern by the skin effect d. is higher for a solid dielectric than for air 

. Impedance inversion may be obtained with a. a short"circuited stub  b. an open"circuited stub c. a 0ua#te#/%a&e line d. a half"wave line !. 5hort"circuited stubs are preferred to open"circuited stubs because the latter are a. more difficult to make an connect  b. made sion line of awith transmis a different characteristic impedance c. liable t$ #aiate d. incapable of giving a full range of reactances $. For transmission"line load matching over a range of fre#uencies, it is  best to use a a. balun  b. broadband directional coupler  c. $uble "tub d. single stub of adBustable position



 +! ,

+. %he main disadvantage of the two"hole directional coupler is a. low directional coupling  b. poor directivity c. high 58  . na##$% ban%ith -. %o couple a coa&ial line to a parallel"wire line, it is best to use a a. slotted line b. balun c. directional coupler  d. #uarter"wave transformer  . Indicate the three types of transmission line energy losses. a. I 2 R, R L , and temperature b. Raiati$n= I 2 R= an ielect#ic heatin) c. ?ielectric separation, insulation breakdown, and radiation d. 6onductor heating, dielectric heating, and radiation resistance. 1(. Indicate the

 

true statement below. %he directional coupler is

a. a device used to connect a transmitter to a directional antenna  b. a c$u'lin) e&ice f$# !atchin) i!'eance c. a device used to measure transmission line power  d. an 58 measuring instrument

RADIATION AND PROPA;ATION OB A6ES 1. Indicate which one of the following terms applies to troposcatter   propagation a. 5I?s b. Bain) c. 'tmospheric storms d. Faraday rotation 2. 9:F waves are used for some type of services because a. of the low powers re#uired  b. the transmitting antennas are of convenient si*e c. the( a#e &e#( #eliable d. the penetrate the ionosphere easily 3. Indicate which of the following fre#uencies    beyond"the"hori*on terrestrial communications without repeaters a. 2( k)*  b. 1! M)* c. (( M)* . , ;H2 . )igh"fre#uency waves are a. absorbed by the F 2 layer   b. reflected by the Dlayer  c. capable of use for long"distance communications on the moon . affecte b( the "$la# c(cle !. ?istances near the skip distance should be used for the sky"wave  propagation a. to avoid tilting b. t$ '#e&ent "(/%a&e an u''e# #a( inte#fe#ence c. to avoid the Faraday effect d. so as nor to e&ceed the critical fre#uency $. ' ship"to"ship communications system is plagued by fading. %he best solution seems to be use of  a. a more directional antenna  b. a broadband antenna c. f#e0uenc( i&e#"it( d. space diversity

cannot   be used for reliable

+. ' range of microwave fre#uencies more easily passed by the atmosphere than are the others is called a a. %in$%  b. critical fre#uency c. gyro fre#uency range d. resonance in the atmosphere

-. Fre#uencies in the 0)F range normally propagate by means of  a. ground waves  b. sky waves c. surface waves . "'ace %a&e" . %ropospheric scatter is used with fre#uencies in the following range a. )F  b. 9)F c. UHB d. 9:F 1(. %he ground wave eventually disappears, as one moves away from the transmitter, because of  a. interference from the sky wave  b. loss of line"of"sight conditions c. ma&imum single"hop distance limitation . tiltin) 11. In electromagnetic waves, polari*ation a. is caused by reflection b. i" ue t$ the t#an"&e#"e natu#e $f the %a&e" c. results from the longitudinal nature of the waves d. is always vertical in an isotropic medium 12. 's electromagnetic waves travel in free space, only one of the following can happen to them a. absorption b. attenuati$n c. refraction d. reflection 13. %he absorption of radio waves by the atmosphere depends on a. thei# f#e0uenc(  b. their distance from the transmitter  c. the polari*ation of the waves d. the polari*ation of the atmosphere

1. lectromagnetic waves are refracted when they a. 'a"" int$ a !eiu! $f iffe#ent ielect#ic c$n"tant  b. are polari*ed at right angles to the direction of propagation c. encounter a perfectly conducting plane d. pass through a small slot in a conducting plane

1!. ?iffraction of electromagnetic waves a. is caused by reflections from the ground  b. arises only with spherical wavefronts c. will occur when the waves pass through a large slot . !a( $ccu# a#$un the e)e $f a "ha#' $b"tacle 1$. hen microwave signals follow the curvature of the earth, this is known as a. the dayFara effect b. uctin) c. tropospheric scatter  d. ionospheric reflection 1+. )elical antennas are often used for satellite tracking at 9)F because of  a. troposcatter   b. superrefraction c. ionospheric ion refract . the Ba#aa( effect

ANTENNAS 1. 'n ungrounded antenna near the ground a. acts as a single antenna of twice the height  b. is unlikely to need a ground screen c. act" a" an antenna a##a( d. must be hori*ontally polari*ed 2. ne of the following consists of nonresonant antennas a. The #h$!bic antenna  b. %he folded dipole c. %he end"fire array d. %he broadside array

3. ne of the following is very useful as a multiband )F receiving antenna. %his is the a. conical horn  b. folded dipole c. l$) 'e#i$ic d. s#uare loop . hich of the following antennas is best e&cited from a waveguide/ a.

a. large ma&imum range  b. good target discrimination c. difficult target ac#uisition . inc#ea"e ca'tu#e a#ea . %he radar cross section of a target =indicate the

 

a. depends on the fre#uency used  b. may be reduced by special coating of the target c. depends on the aspect of a target, if this nonspherical . i" e0ual t$ the actual c#$""/"ecti$nal a#ea f$# "!all ta#)et" !. Flat"topped rectangular pulses must be transmitted in radar to =indicate the   false statement> a. allow a good minimum range b. !ae the #etu#ne ech$e" ea"ie# t$ i"tin)ui"h f#$! n$i"e c. prevent fre#uency changes in the magnetron d. allow accurate range measurements $. ' high C8F will =indicate the

 

false

statement>

a. make the returned echoes easier to distinguish from noise  b. make target tracking easier with conical scanning c. inc#ea"e the !a*i!u! #an)e d. have no effect on the range resolution

false

statement>

+. %he IF bandwidth of a radar receiver is inversely proportional to the a. 'ul"e %ith  b. pulse repetition fre#uency c. pulse interval d. s#uare root of the peak transmitted power 

-. If a return echo arrives after the allocated pulse interval, a. it will interfere with the operation of the transmitter   b. the receiver might be overloaded c. it will not be received . the ta#)et %ill a''ea# cl$"e# than it #eall( i" . 'fter a target has been ac#uired, the best scanning system for tracking is a. nodding  b. spiral c. c$nical d. helical 1(. If the target cross section is changing, the best system for accurate tracking is a. lobe switching  b. se#uential lobing c. conical anning sc . !$n$'ul"e 11. %he biggest disadvantage of 6 ?oppler radar is that a. it does not give the target veloci b. it $e" n$t )i&e the ta#)et #an)e c. a transponder is re#uired at the target d. it does not give the target position

ty

12. %he ' scope displays a. the target position and range b. the ta#)et #an)e= but n$t '$"iti$n c. the target position, but not range d. neither range nor position, but not only velocity 13. %he ?oppler effect is used in =indicate the a. !$&in)/ta#)et 'l$ttin) $n the PPI  b. the M%I system c. FM radar  d. 6 radar 

 

false

statement>

1. %he   coho in M%I radar operates at the a. inte#!eiate f#e0uenc(  b. transmitted fre#uency c. received fre#uency d. pulse repetition fre#uency

1!. %he function of the #uart* delay line in a n M%I radar is to a. hel' in "ubt#actin) a c$!'lete "can f#$! the '#e&i$u" "can  b. match the phase of the coho and the stalo c. match the phase of the coho and the output oscillator  d. delay a sweep so that the ne&t sweep can be subtracted from it

1$. ' solution to the Hblind speed problem is a. to change the ?oppler fre#uency b. t$ &a#( the PRB c. to use monopulse d. to use M%I 1+. Indicate which one of the following applications or advantages of  radar beacons is   false: a. %arget identification  b. 4avigation c. 9ery significant e&tension of the ma&imum range . M$#e accu#ate t#acin) $f ene!( ta#)et" 1-. 6ompared with other types of radar, phased array radar has the following advantages =indicate the   false statement> a. very fast scanning  b. ability to track and scan simultaneously c. ci#cuit "i!'licit( d. ability to track many targets simultaneously

PULSE COMMUNICATIONS 1. Indicate which of the following is

not  a binary code

a. M$#"e  b.