ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-Microwave,EMFT,Communication Part-1


Q1 IN A COMMUNICATION SYSTEM NOISE IS MOST LIKELY TO AFFECT THE SIGNAL
 (a) at the transmitter
 (b)in the channel
 (c)in the information source
 (d)at the destination
 ans-b

Q2 INDICATE THE FALSE STATEMENT .MODULATION IS USED TO
 (a)reduce the bw used
 (b)separate different transmissions
 (c)ensure that intelligence may be transmitted over long distances
 (d)allow the use of practical antenna
 ans-a

Q3 ONE OF THE FOLLOWING NOISE BECOME OF GREAT IMPORTANCE AT HIGH FREQUENCY.IT
IS THE
 (a)shot noise
 (b)random noise
 (c)impulse noise
 (d)transit time noise
 ans-d

Q4 INDICATE THE FALSE STATEMENT
 (a)hf mixer are generally nosier than hf amplifiers
 (b)impulse noise voltage is independent of bw
 (c)thermal noise is independent of frequency at which it is measured
 (d)industrial noise is usually of impulse type
 ans-b
Q5 THE VALUE OF THE RESISTOR CREATING THERMAL NOISE IS DOUBLED .THE NOISE POWER
IS
 (a)halved
 (b)quadrupled
 (c)doubled
 (d)unchanged
 ans-d

Q6 ONE OF THE FOLLOWING IS NOT A USEFUL QUANTITY FOR COMPARING THE NOISE
PERFORMANCE OF RECEIVERS
 (A)i/p noise voltage
 (b)equivalent noise resistance
 (c)noise temp
 (d)noise figure
 ans-a

Q7 INDICATE THE NOISE WHOSE SOURCE IS IN A CATEGORY DIFFERENT FROM THAT OF
OTHER THREE
 (A)solar noise
 (B)cosmic noise
 (C)atmospheric noise
 (D)galgatic noise
 ans-c

Q8 IN A LOW LEVEL AM SYSTEM ,AMPLIFIERS FOLLOWING THE MODULATED SIGNAL MUST BE
 (a)linear
 (b)harmonic devices
 (c)class c amplifiers
 (d)non linear devices
 ans-a

Q9 LEAK TYPE BIAS IS USED IN A PLATE MODULATED CLASS C AMPLIFIER TO
 (A)prevent tuned circuit damping
 (b)prevent excessive grid current
 (c)prevent over modulation
 (d)increase the bw
 ans-b

Q10 THE O/P STAGE OF A TELEVISION TRANSMITTER IS MOST LIKELY TO BE A
 (a)plate modulated class c amplifier
 (b)grid modulated class c amplifier
 (c)screen modulated class c amplifier
 (d)grid modulated class a amplifier
 ans-b
Q11 THE MODULATION INDEX OF AN AM IS CHANGED FROM 0 TO 1 .THE TRANSMITTED POWER
IS
 (a)unchanged
 (b)halved
 (c)doubled
 (d)increased by 50%
 ans-d

Q12 ONE OF THE ADVANTAGE OF BASE MODULATION OVER COLLECTOR MODULATION OF A
TRANSISTOR CLASS C AMPLIFIER IS
 (a)the lower  modulation power is required
 (b)higher power o/p per transistor
 (c)better efficiency
 (d)better linearity
 ans-a

Q13 AM IS USED FOR BROADCASTING BECAUSE
 (A)it is more noise immune than other information system
 (b)compared with other it requires less transmitting power
 (c)its use avoids receiver complexity
 (d)no other modulation system can provide the necessary bw for high
fidelity
 ans-c

Q14 THE MOST COMMONLY USED FILTERS IN SSB GENERATIONS ARE
 (A)mechanical
 (b)rc
 (c)lc
 (d)low pass
 ans-a

Q15 IN AN SSB TRANSMITTER ONE IS MOST LIKELY TO FIND A
 (a)class c audio amplifier
 (b)tuned amplifier
 (c)class b rf amplifier
 (d)class a rf o/p amplifier
 ans-c

Q16 ONE OF THE FOLLOWING CANNOT BE USED TO REMOVE THE UNWANTED SIDEBAND IN SSB.
THIS IS THE
 (A)filter system
 (b)phase shift method
 (c)third method
 (d)balanced modulator
 ans-d

Q17 IN THE SPECTRUM OF A FM WAVE
 (a)the carrier frequency disappears when the modulation index is large
 (b)the amplitude of any side band depends on the modulation index
 (c)the total number of sidebands depends on the modulation index
 (d)the carrier frequency cannot disappear
 ans-b

Q18 THE DIFFERENCE B/W PHASE N FREQUENCY MODULATION
 (a)is purely theoretical because they are same in practice
 (b)ia too great to make the two system compatible
 (c)lies in the poorer audio response of phase modulation
 (d)lies in different definitions of the modulation index
 ans-d

Q19 AN FM SIGNAL WITH MODULATION INDEX m  IS PASSED THROUGH A FREQUENCY
TRIPLER THE WAVE IN THE O/P OF THE TRIPLER WIILL HAVE A MODULATION INDEX OF
 (A)m/3
 (b)m
 (c)3m
 (d)9m
 ans-c

Q20 AN FM, SIGNAL WITH DEVIATION “a” IS PASSED THROUGH A MIXER N HAS
ITS FREQUENCY REDUCED 5 FOLD .THE DEVIATION IN THE O/P OF THE MIXER IS
 (a)5a
 (b)indeterminate
 (c)a/5
 (d)a
 ans-d

Q21 A PRE EMPHASIS CIRCUIT PROVIDES EXTRA NOISE IMMUNITY BY
 (a)boosting the base frequency
 (b)amplifying the higher audio frequency
 (c)pre amplifying the whole audio band
 (d)converting the pm to fm
 ans-b

Q22 SINCE NOISE PM THE FM WAVE ,AS THE NOISE SIDEBAND FREQUENCY APPROACHES THE
CARRIER FREQUENCY ,THE NOISE AMPLITUDE
 (a)remains constant
 (b)decreases
 (c)increases
 (d)is equalised
 ans-b

Q23 WHEN THE MODULATING FREQUENCY IS DOUBLED ,THE MODULATION INDEX IS HALVED
AND THE MODULATING VOLTAGE IS REMAINS CONSTANT,THE MODULATION SYSTEM IS
 (a)am
 (b)pm
 (c)fm
 (d)any of the three
 ans-c

Q24 INDICATE WHICH OF THE FOLLOWING IS NOT A ADVANTAGE OF FM OVER AM
 (a)better noise immunity is provided
 (b)lower bw is required
 (c)the transmitted power is more useful
 (d)less modulating power is required
 ans-b

Q25 ONE OF THE FOLLOWING IS INDIRECT WAY OF GENERATING FM  IS THE
 (a)reacatnce fet modulator
 (b)varactor diode modulator
 (c)armstrong method
 (d)reactance bipolar transistor modulator
 ans-c

Q26 IN AN FM STEREO MULTIPLEXING TRANSMISSION ,THE
 (a)sum signal modulates the 19 khz sun carrier
 (b)difference signal modulates the 19 khz sub carrier
 (c)difference signal modulates 38 khz sub carrier
 (d)difference signal modulates 67 khz sub carrier
 ans-c

Q27 INDICATE WHICH OF THE FOLLOWING STATEMENTS ABOUT THE ADVANTAGE OF THE PHASE
DISCRIMINATOR OVER THE SLOPE DETECTOR IS FALSE
 (a)much easier alignment
 (b)better linearity
 (c)greater limiting
 (d)fewer tuned circuit
 ans-c

Q28 SHOW WHICH OF THE FOLLOWING STATEMENTS ABOUT THE AMPLITUDE LIMITER IS
UNTRUE
 (a)the circuit is always biased in class c ,by virtue of leak-type bias.
 (b)when i/p increases past the threshold limiting the gain decreases to
keep the o/p constant
 (c)the o/p must be tuned
 (d)leak type bias must be used
 ans-a

Q29 IN A RADIO RECEIVER WITH SIMPLE AGC
 (a)an increase in signal strength produces more agc
 (b)the audio stage gain is normally controlled by the agc
 (c)the faster the agc time constant ,the more accurate the o/p
 (d)the highest agc voltage is produced b/w stations
 ans-a

Q30 IN A BROADCAST SUPERHETRODYNE RECEIVER ,THE
 (a)local oscillator operates below the signal frequency
 (b)mixer i/p must be tuned to the signal frequency
 (c)local oscillator frequency is normally doubled the if
 (d) rf amplifier normally works at 455 khz above the carrier
 ans-b

Q31 TO PREVENT OVER LOADING OF THE LAST IF AMPLIFIER IN A RECEIVER ,ONE SHOULD
USE
 (A)squelch
 (b)variable sensitivity
 (c)variable selectivity
 (d)double conversion
 ans-b

Q32 IN A RATIO DETECTOR
 (a)the linearity is worse than in a phase discriminator
 (b)stabilisation against signal strength variation is provided
 (c)the o/p is twice obtainable from a similar phase discriminator
 (d)the circuit is same as in a discriminator ,except that the diodes are
reversed
 ans-a

Q33 THE TYPICAL SQUELACH CIRCUIT
 (a)cuts off an audio amplifier when the carrier is absent
 (b)eliminates the rf interference when the signsl is weak.
 (c)cuts off an amplifier when the agc is maximum
 (d)cuts off an amplifier when the agc is minimum
 ans-a

Q34 INDICATE THE FALSE STATEMENT IN CONNECTION WITH COMMUNICATION RECEIVERS
 (a),the noise limiter cuts off the  receiver’s o/p during a noise
pulse
 (b)a product demodulator could be used for the reception of morse code
 (c)double conversions is used to improve image rejection
 (d)variable sensitivity is used to eliminate selective fading
 ans-d

Q35 THE CONTROLLED OSCILLATOR SYNTHESIZER IS SOMETIMES PREFFERED TO THE DIRECT
ONE BECAUSE
 (a)it is a simpler piece of instrument
 (b)it’s frequency stability is better
 (c)it does not require crystal oscillator
 (d)it is relatively free of spurious noise
 ans-d
Q35 THE FREQUENCY GENERATED BY EACH DECADE IN A DIRECT FREQUENCY SYNTHESIZER IS
MUCH HIGHER THAN THE FREQUENCY SHOWN,THIS DONE TO
 (A)reduce the spurious frequency problem
 (b)increase the frequency stability of the synthesizer
 (c)reduce the number of decades
 (d)reduce the number of crystal required
 ans-a

Q36 INDICATE WHICH OF THE FOLLOWING CAN’T DEMODULATE SSB SIGNAL
 (a)balanced modulator
 (b)product modulator
 (c)bfo
 (d)phase discriminator
ans-d

Q37 IF AN AMPLIFIER IS USED AS THE FIRST AF AMPLIFIER IN A TRANSISTOR RECEIVER
,THIS WILL HAVE THE EFFECT OF
 (a)improving the effectiveness of the agc
 (b)reducing the effect of -ve peak clipping
 (c)reducing the effect of noise at low modulation depths
 (d)improving the selectivity of the receiver
 ans-b

Q38 THE IMAGE FREQUENCY OF AN SUPERHETRODYNE RECEIVER IS
 (a)is created within the receiver it self
 (b)is due to insufficient adjacent channel rejection
 (c)is not rejected by if tuned circuits
 (d)is independent of the frequency at which the receiver is tuned
 ans-c

Q39 ONE OF THE MAIN FUNCTION OF THE RF AMPLIFIER IN SUPERHETRODYNE RECEIVER IS
TO
 (a)provide improve tracking
 (b)permit better adjacent channel rejection
 (c)increase the tuning range of the receiver
 (d)improve the rejection of the image frequency
 ans-d

Q40 A RECEIVER HAS POOR IF SELECTIVITY.IT WILL THEREFORE  ALSO HAVE POOR
 (a)blocking
 (b)double-spotting
 (c)diversity reception
 (d)sensitivity
 ans-a

Q41 THREE POINT TRACKING IS ACHIEVED WITH
 (a)variable selectivity
 (b)the padder capacitor
 (c)double spotting
 (d)double conversion
 ans-b

Q42 THE LOCAL OSCILLATOR OF A BROAD CAST RECEIVER IS TUNED TO O FREQUENCY
HIGHER THAN THE INCOMING FREQUENCY
 (a)to help the image frequency rejection
 (b)to permit easier tracking
 (c)because otherwise an intermediate frequency could not be produced
 (d)to allow adequate frequency coverage without switching
 ans-d

Q43 A LOW RATIO OF THE AC TO THE DC LOAD IMPEDANCE OF A DIODE DETECTOR RESULTS
IN
 (a)diagonal clipping
 (b)poor agc operation
 (c)-ve peak clipping
 (d)poor af response
 ans-c

Q44 THE INTERMEDIATE FREQUENCY IS VERY HIGH(INDICATE FALSE STATEMENT)
 (a)image frequency rejection is very good
 (b)the local oscillator need not be extremely stable
 (c)the selectivity Will be poor
 (d)tracking will be improved
 ans-d

Q45 WHEN A RECEIVER HAS A GOOD BLOCKING PERFORMANCE ,THIS MEANS THAT
 (a)it does not suffer from double spotting
 (b)it’s image frequency rejection is poor
 (c)it is unaffected by agc derived from near by transmission
 (d)it’s detector suffers from burnout
 ans-c

Q46 INDICATE THE FALSE STATEMENT.THW SWR ON A TRANSMISSION LINE IS INFINITY
,THE LINE IS TERMINATED IN
 (A)a short circuit
 (b)a complex impedance
 (c)an open circuit
 (d)a pure reactance
 ans-b

Q47 A(75-J50)ohm IS CONNECTED TO A COAXIAL LINE OF Z0=75 ohm AT 10GHZ .THE BEST
WAY OF MATCHING CONSISTS IN CONNECTING
 (a)a short circuit stab at the load
 (b)an inductance at the load
 (c)a capacitance at some specific distance from the load
 (d)a short circuit stab at some specific distance from the load
 ans-d

Q48 THE VELOCITY FACTOR OF A TRANSMISSION LINE
 (a)depends on the dielectric constant of the material used
 (b)increases the velocity along the transmission line
 (c)is governed by skin effect
 (d)is higher for a solid dielectric than for air
 ans-a

Q49 IMPEDANCE INVERSION MAY BE OBTAINED WITH
 (A)a short ckt stub
 (B)an open ckt stub
 (c)a quarter wave line
 (d)a half wave line
 ans-c

Q50 SHORT CKT STUBS ARE PREFERRED TO OPEN CKT STUBS BECAUSE THE LATER ARE
 (a)more difficult to make n connect
 (b)made of transmission line of different characteristics impedance
 (c)liable to radiate
 (d)incapable of giving full range of reactances
 ans-c

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ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-Microwave,EMFT,Communication Part-2
सामान्य विज्ञान(General Science)-Important Questions & Answers One liner PDF for SSC JE,NMRC SC/TO,JMRC,CIL EXAM PART 5

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