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

Accepted Answer

FM transmitting and receiving equipment is generally more costly than AM equipment due to the complexity of FM signal generation and demodulation processes.

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

Accepted Answer

The initial fractional change in frequency is calculated as (10000 Hz - 50 Hz) / 50 Hz = 9950 Hz / 50 Hz = 199 = approximately 200. After frequency translation, the signal is centered around 106 Hz, so the fractional change is (10600 Hz - 106 Hz) / 106 Hz = 10494 Hz / 106 Hz = approximately 99, which is close to 100, but when considering the correct interpretation of the question, which involves the comparison of bandwidths rather than the direct calculation of fractional change post-translation, the correct answer reflects the minimal change due to the high carrier frequency, making the fractional change very small, closer to 1.01, acknowledging a misunderstanding in the initial explanation.

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

Accepted Answer

The width of the channel in frequency modulation is determined by the formula: Channel Width = 2 * (Maximum Modulation Frequency + Deviation Frequency). Here, the audio signal frequency range is 100 to 5000 kHz, so the maximum modulation frequency is 5000 kHz. However, in this context, it seems there's a misunderstanding in the question's phrasing regarding the typical audio signal range for modulation, which is more likely to be 100 Hz to 5000 Hz (not kHz). Assuming the correct range is 100 Hz to 5000 Hz, the channel width would be 2 * 5000 Hz = 10 kHz, since there's no deviation frequency mentioned, and we consider only the maximum audio frequency for simplicity.

Question 4

Which one of the following is analog?
A)pcm
B)pwm
C)delta modulation
D)differential pcm

Accepted Answer

Pulse Width Modulation (PWM) is an analog modulation technique where the width of the pulses is varied according to the amplitude of the analog signal.

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

Accepted Answer

Frequency Modulation (FM) requires a larger bandwidth compared to Amplitude Modulation (AM). According to Carson's rule, the total bandwidth needed for FM is twice the sum of the maximum deviation frequency and the maximum modulating signal frequency, which is typically much larger than the bandwidth required for an equivalent AM signal.

Question 6

Which of the following is a digital modulation technique?
A)pcm
B)psk
C)dm
D)all

Accepted Answer

The answer of Which of the following is a digital...

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

Accepted Answer

A monostable multivibrator is used to generate Pulse Duration Modulation (PDM) because it can produce a single pulse of a specific duration in response to an input trigger.

Question 8

SSB can be generated by
A)filter method
B)phase cancellation method
C)good attenuation characteristics
D)all of the above

Accepted Answer

SSB (Single Side Band) can be generated by various methods including the filter method, phase cancellation method, and using devices with good attenuation characteristics to suppress the unwanted sideband.

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

Accepted Answer

The output of an ideal low pass filter is a white noise process, which means that the samples are statistically independent.

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

Accepted Answer

Peak clipper circuits are used in radio transmitters to prevent overmodulation, which can cause distortion and interference with adjacent channels.

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

Accepted Answer

In a low level amplitude modulation system, the amplifiers following the modulated stage must be linear devices to accurately amplify the modulated signal without distorting its amplitude or phase. Non-linear amplifiers would distort the signal, and class C amplifiers are typically used for high-efficiency applications but are not linear. Harmonic devices are not a category of amplifiers.

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

Accepted Answer

The answer of Under ordinary circumstances, impulse noise can be...

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

Accepted Answer

In frequency modulation (FM), when the modulating frequency is lowered while keeping the modulating voltage constant, the spacing between the sidebands increases. However, the amplitude of the distant sidebands increases because the modulation index (which is proportional to the ratio of the modulating voltage to the modulating frequency) increases, leading to stronger sidebands further away from the carrier frequency.

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

Accepted Answer

The Nyquist rate is twice the highest frequency of interest. In this case, the highest frequency of interest is 10 kHz, so the Nyquist rate is 20 kHz. The bandwidth required is therefore 20 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

Accepted Answer

The answer of It is found that a ship to...

Question 16

In practical commercial FM system, channel bandwidth is
A)150 khz
B)100 khz
C)88 mhz
D)108 mhz

Accepted Answer

In practical commercial FM systems, the channel bandwidth is typically 150 kHz. This allows for the transmission of high-fidelity audio signals and accommodates the deviation and modulating signal frequencies used in FM broadcasting.

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

Accepted Answer

Polarization is due to the transverse nature of electromagnetic waves, where the electric field oscillates perpendicular to the direction of wave propagation.

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

Accepted Answer

The answer of The maximum power output of a standard...

Question 19

PAM stands for
A)pulse analogue modulation
B)phase analogue modulation
C)pulse amplitude modulation
D)phase amplitude modulation

Accepted Answer

PAM stands for Pulse Amplitude Modulation, which is a technique where the amplitude of each pulse in a signal is varied according to the sample value of the message signal.

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

Accepted Answer

The characteristic impedance of a twin wire feeder commonly used for TV signals is about 300 ohm. This type of transmission line is often used for connecting antennas to televisions, especially in older or more traditional setups.

Quiz 3: Radio Transmission and Modulation Techniques

FM transmitting and receiving equipment as compared to AM equipment is

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

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.

Which one of the following is analog?

The disadvantage of FM over AM is that

Which of the following is a digital modulation technique?

Which of the following is used to generate PDM?

SSB can be generated by

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

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

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

Under ordinary circumstances, impulse noise can be reduced in

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

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

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

In practical commercial FM system, channel bandwidth is

In EM waves, polarization

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

PAM stands for

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