WorksheetsTop Communication Systems Questions
Total questions: 61
Worksheet time: 31mins
A cordless telephone using separate frequencies for transmission in base and portable units is known as
duplex arrangement
half duplex arrangement
either (a) or (b)
neither (a) nor (b)
For attenuation of high frequencies we should use
shunt capacitance
series capacitance
inductance
resistance
A modem is classified as low speed if data rate handled is
upto 100 bps
upto 250 bps
upto 400 bps
upto 600 bps
VSB modulation is preferred in TV because
it reduces the bandwidth requirement to half
it avoids phase distortion at low frequencies
it results in better reception
none of the above
A woofer should be fed from the input through a
low pass filter
high pass filter
band pass filter
band stop filter
Which of the following is an indirect way of generating FM?
Armstrong modulator
Varactor diode modulator
Reactance FET modulator
Reactance bipolar transistor
When the length of antenna is a whole wavelength
the radiation at right angles is zero
the radiation at right angles is maximum
the radiation is zero in all directions
the radiation is maximum in all directions
Circular polarization
is useful in reducing depolarization effect on received wave
involves critical alignment of transmitting and receiving antenna
is useful in discrimination between reception of adjacent beams
none of the above
An FM radio receiver which is tuned to a 91.6 MHz broadcast station may receive an image frequency of __________ MHz.
102.3
113
70.2
80.9
For telegraphy the most commonly used modulation system is
FSK
two tone modulation
PCM
single tone modulation
Commercial Frequency deviation of FM is
70 kHz
75 kHz
80 kHz
65 kHz
The colour of an object is decided by
the reflected colour
the wavelength transmitted through it
reflected colour for opaque object and wavelength transmitted through it for transparent objects
none of the above
In Pulse Code Modulation system
large bandwidth is required
quantising noise can be overcome by companding
quantising noise can be reduced by decreasing the number of standard levels
suffers from the disadvantage of its incompatibly with TDM
If output power of a radio receiver is doubled, its volume is increased by __________ dB.
2
3
1
-3
Which of the following statements is correct?
Convex lens has positive focal power and concave lens have negative focal power
Convex lens has negative focal power and concave lens have positive focal power
All lens have positive focal power
All lens have negative focal power
In Modulation, “carrier” is
resultant wave
speech voltage to be transmitted
voltage with constant frequency, phase or amplitude
voltage for which frequency, phase or amplitude is varied
To eliminate ghosts in the picture
use a longer transmission line
connect a booster
change the antenna orientation of location
twist the transmission line
The frequency range of 300 kHz to 3000 kHz is known as
low frequency
medium frequency
high frequency
very high frequency
Which of the following does not cause losses in optical fibre cables?
Stepped index operation
Impurities
Microbending
Attenuation in glass
For a low level AM system, the amplifiers modulated stage must be
linear devices
harmonic devices
class C amplifiers
non-linear devices
Assertion (A): In FM the frequency of the carrier is varied by the modulating voltage Reason (R): FM and PM are two forms of angle modulation.
Both A and R are correct and R is correct explanation of A
Both A and R are correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
A telephone channel requires a bandwidth of about
1 kHz
3 kHz
10 kHz
50 kHz
For a given carrier wave, maximum undistorted power is transmitted when value of modulation is
1
0.8
0.5
0
As per Shannon-Hartley theorem, a noise less Gaussian channel has
zero capacity
infinite capacity
small capacity
none of the above
DVD uses
Laser beam for both recording and playback
Laser beam for recording and video head for playback
Video head for recording and laser beam for playback
None of the above
Fourier analysis indicate that a square wave can be represented as
a fundamental sine wave and odd harmonics
a fundamental sine wave and even harmonics
a fundamental sine wave and harmonics
fundamental and subharmonic sine waves
FM transmitting and receiving equipment as compared to AM equipment is
costly
cheaper
almost equally costly
none of the above
An audio signal (say from 50 Hz to 10000 Hz) is frequency translated by a carrier having a frequency of 106 Hz. The values of initial (without frequency translation) and final (after frequency translation) fractional change in frequency from one band edge to the other are
200 and 1.01
200 and 10.01
200 and 100.1
200 and 200
If in a broadcasting studio, a 1000 kHz carrier is modulated by an audio signal of frequency range 100-5000 kHz, the width of channel is __________ kHz.
5
4.9
995
10
Which one of the following is analog?
PCM
PW
Which one of the following is analog?
PCM
PWM
Delta modulation
Differential PCM
The disadvantage of FM over AM is that
high output power is needed
high modulating power is needed
noise is very high for high frequency
large bandwidth is required
Which of the following is a digital modulation technique?
PCM
PSK
DM
All
Which of the following is used to generate PDM?
Free running multi-vibrator
Monostable multi-vibrator
JK flip-flop
Schmitt trigger
SSB can be generated by
filter method
phase cancellation method
good attenuation characteristics
all of the above
A zero mean white Gaussian noise is passed through an ideal low pass filter of bandwidth 10 kHz. The output of the samples so obtained would be
correlated
statistically independent
uncorrelated
orthogonal
What is the purpose of peak clipper circuits in radio transmitters?
To prevent overmodulation
To reduce bandwidth
To increase bandwidth
To regulate oscillator I/P voltage
In case of low level amplitude modulation system, the amplifiers following the modulated stage must be
class C amplifiers
linear devices
non-linear devices
harmonic devices
Under ordinary circumstances, impulse noise can be reduced in
FM only
AM only
both AM and FM
none of the above
In case of frequency modulation, modulating voltage remains constant if the modulating frequency is lowered, then
amplitude of distant sidebands decreases
amplitude of distant sidebands increases
amplitude of distant sidebands remains constant
amplitude of distant sidebands first increases, then decreases
If sampling is done at the rate of 10 kHz. The bandwidth required is
35 kHz
70 kHz
10 kHz
1280 kHz
It is found that a ship to ship communication suffers from fading. This can be avoided by using
space diversity
frequency diversity
broad band antenna
directional antenna
Skip distance depends on time of day and angle of incidence.
True
False
In practical commercial FM system, channel bandwidth is
150 kHz
100 kHz
88 MHz
108 MHz
In EM waves, polarization
is always vertical in an isotropic medium
is caused by reflection
is due to transverse nature of waves
results from longitudinal nature of waves
The maximum power output of a standard A earth station over the total band allocated to satellite communication is about
0.5 kW
8 kW
20 kW
50 kW
PAM stands for
Pulse Analogue Modulation
Phase Analogue Modulation
Pulse Amplitude Modulation
Phase Amplitude Modulation
The characteristic impedance of a twin wire feeder used for TV signals is about
1000 ohm
500 ohm
300 ohm
100 ohm
In a FM receiver, amplitude limiter
amplifiers low frequency signals
reduces the amplitude of signals
eliminates any change in amplitude of received FM signals
none of the above
A buffer amplifier is
a double-tuned amplifier
a high gain D.C. amplifier
a cathode follower stage
none of the above
Leak type bias is used in plate modulated class C amplifier to
increase the bandwidth
prevent over modulation
prevent excessive grid current
prevent tuned circuit damping
The direction of rotation of a CD is
clockwise
anticlockwise
clockwise or anticlockwise depending on frequency of data stored
mostly anticlockwise but some times clockwise
One of the advantages of base modulation over collector modulation of a transistor class C amplifier is
improved efficiency
better linearity
high power output per transistor
the lower modulating power requirement
Full duplex operation-permits transmission in both directions at the same time.
True
False
In a TV receiver antenna the length of reflector rod
is the same as that of dipole
is less than that of dipole
is more than that of dipole
may be equal, more or less than that of dipole
The modulation index of an FM is changed from 0 to 1. How does the transmitted power change?
Gets halved
Gets doubled
Gets increased by 50 percent
Remains unchanged
For AM receivers the standard IF frequency is
106 kHz
455 kHz
1.07 MHz
10.7 MHz
For a plate-modulated class C amplifier the plate supply voltage is E. The maximum plate cathode voltage could be almost high as
2E
3E
4E
6E
In TV systems, equalising pulses are sent during
horizontal blanking
vertical blanking
serrations
horizontal retrace
A three stage telephone switching structure is to have 128 input and 128 output terminals. There are 16 first stage and 16 third stage matrices. To avoid blocking the number of intermediate paths required is
16
15
8
1
The main function of a balanced modulator is to
produce balanced modulation of a carrier wave
produce 100% modulation
suppress carrier signal in order to create a single-sideband or double sideband
limit noise picked by a receiver
