Deck 3: Radio Transmission and Modulation Techniques

Question 1

FM transmitting and receiving equipment as compared to AM equipment is

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

Answer 1

costly

Question 2

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

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

Answer 2

200 and 1.01

Question 3

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.

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

Answer 3

10

Question 4

Which one of the following is analog?

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

Question 5

The disadvantage of FM over AM is that

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 6

Which of the following is a digital modulation technique?

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

Question 7

Which of the following is used to generate PDM?

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

Question 8

SSB can be generated by

A)filter method
B)phase cancellation method
C)good attenuation characteristics
D)all of the above

Question 9

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

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

Question 10

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

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

Question 11

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

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

Question 12

Under ordinary circumstances, impulse noise can be reduced in

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

Question 13

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

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 14

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

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

Question 15

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

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

Question 16

In practical commercial FM system, channel bandwidth is

A)150 khz
B)100 khz
C)88 mhz
D)108 mhz

Question 17

In EM waves, polarization

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 18

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

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

Question 19

PAM stands for

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

Question 20

The characteristic impedance of a twin wire feeder used for TV signals is about

A)1000 ohm
B)500 ohm
C)300 ohm
D)100 ohm

Question 21

In a FM receiver, amplitude limiter

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 22

A buffer amplifier is

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

Question 23

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

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

Question 24

The direction of rotation of a CD is

A)clockwise
B)anticlockwise
C)clockwise or anticlockwise depending on frequency of data stored
D)mostly anticlockwise but some times clockwise

Question 25

One of the advantages of base modulation over collector modulation of a transistor class C amplifier is

A)improved efficiency
B)better linearity
C)high power output per transistor
D)the lower modulating power requirement