Question 1

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

Accepted Answer

A)  200 and 1.01
B)  200 and 10.01
C)  200 and 100.1
D)  200 and 200 A

Question 2

Leak type bias is used in plate modulated class C amplifier to

Accepted Answer

A)  increase the bandwidth
B)  prevent over modulation
C)  prevent excessive grid current
D)  prevent tuned circuit damping C

Question 3

Under ordinary circumstances, impulse noise can be reduced in

Accepted Answer

A)  fm only
B)  am only
C)  both am and fm
D)  none of the above A

Question 4

In case of low level amplitude modulation system, the amplifiers following the modulated stage must be

Accepted Answer

A)  class c amplifiers
B)  linear devices
C)  non-linear devices
D)  harmonic devices

Question 5

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

Accepted Answer

A)  correlated
B)  statistically independent
C)  uncorrelated
D)  orthogonal

Question 6

In case of frequency modulation, modulating voltage remains constant if the modulating frequency is lowered, then

Accepted Answer

A)  amplitude of distant sidebands decreases
B)  amplitude of distant sidebands increases
C)  amplitude of distant sidebands remains constant
D)  amplitude of distant sidebands first increases, then decreases

Question 7

What is the purpose of peak clipper circuits in radio transmitters?

Accepted Answer

A)  to prevent overmodulation
B)  to reduce bandwidth
C)  to increase bandwidth
D)  to regulate oscillator i/p voltage

Question 8

Which of the following is used to generate PDM?

Accepted Answer

A)  free running multi-vibrator
B)  monostable multi-vibrator
C)  jk flip-flop
D)  schmitt trigger

Question 9

The disadvantage of FM over AM is that

Accepted Answer

A)  high output power is needed
B)  high modulating power is needed
C)  noise is very high for high frequency
D)  large bandwidth is required

Question 10

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.

Accepted Answer

A)  5
B)  4.9
C)  995
D)  10

Question 11

The maximum power output of a standard A earth station over the total band allocated to satellite communication is about

Accepted Answer

A)  0.5 kw
B)  8 kw
C)  20 kw
D)  50 kw

Question 12

In EM waves, polarization

Accepted Answer

A)  is always vertical in an isotropic medium
B)  is caused by reflection
C)  is due to transverse nature of waves
D)  results from longitudinal nature of waves

Question 13

FM transmitting and receiving equipment as compared to AM equipment is

Accepted Answer

A)  costly
B)  cheaper
C)  almost equally costly
D)  none of the above

Question 14

PAM stands for

Accepted Answer

A)  pulse analogue modulation
B)  phase analogue modulation
C)  pulse amplitude modulation
D)  phase amplitude modulation

Question 15

A buffer amplifier is

Accepted Answer

A)  a double-tuned amplifier
B)  a high gain d.c. amplifier
C)  a cathode follower stage
D)  none of the above

Question 16

Which of the following is a digital modulation technique?

Accepted Answer

A)  pcm
B)  psk
C)  dm
D)  all

Question 17

Which one of the following is analog?

Accepted Answer

A)  pcm
B)  pwm
C)  delta modulation
D)  differential pcm

Question 18

In a FM receiver, amplitude limiter

Accepted Answer

A)  amplifiers low frequency signals
B)  reduces the amplitude of signals
C)  eliminates any change in amplitude of received fm signals
D)  none of the above

Question 19

If sampling is done at the rate of 10 kHz. The bandwidth required is

Accepted Answer

A)  35 khz
B)  70 khz
C)  10 khz
D)  1280 khz

Question 20

It is found that a ship to ship communication suffers from fading. This can be avoided by using

Accepted Answer

A)  space diversity
B)  frequency diversity
C)  broad band antenna
D)  directional antenna

Exam 3: Radio Transmission and Modulation Techniques