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Test: Single Sideband (SSB) Modulation - Electronics and Communication Engineering (ECE) MCQ


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10 Questions MCQ Test GATE ECE (Electronics) 2024 Mock Test Series - Test: Single Sideband (SSB) Modulation

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Test: Single Sideband (SSB) Modulation - Question 1

The power contained in single sideband in amplitude modulation is

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 1

Concept: 

The total transmitted power for an AM system is given by:

Pc = Carrier Power

m = Modulation Index

Analysis:

The above expression can be expanded to get:

The total power is the sum of the carrier power and the sideband power, i.e.

In conventional AM transmission, the power is equally distributed between the two sidebands, i.e.

∴ The power contained in a single sideband in amplitude modulation is 

Test: Single Sideband (SSB) Modulation - Question 2

How much percentage power will be saved when the carrier and one of the sidebands are suppressed in an AM wave modulated to a depth of 50%?

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 2

Concept:

Total power in AM (PT)= PC ( 1 + μ2/2 ) = PC + PCμ2/2

where;

PC → Carrier power 

μ → modulation index

Power of single sideband = ( PCμ2/2)/2 =  PCμ2/4

Calculation:

Given 

μ = 50% = 0.5

After suppressing carrier and a single sideband :

PT = (PC + PCμ2/2) - (PC + PCμ2/4) = PCμ2/4

Percentage of power will be saved :

= [(PC + PCμ2/2 )- PCμ2/4 ]/PC ( 1 + μ2/2 ) × 100

= (1 + μ2/4)/( 1 + μ2/2 ) × 100

= (1 + (0.5)2/4)/( 1 + (0.5)2/2 ) × 100

94.44 %

Test: Single Sideband (SSB) Modulation - Question 3

Pilot carrier in SSB modulation is used for

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 3

In single-sideband (SSB) modulation only the upper sideband or the lower sideband is transmitted (the carrier is suppressed).

  • The major problem with the detection techniques in SSB is to have a coherent source at the receiver.
  • If the frequency error becomes a function of time then it becomes difficult to recover the original signal.
  • Since demodulation is hard in SSB signals, a low power carrier wave is transmitted with the SSB, which is called PILOT CARRIER.
  •  This can be received and amplified at the receiving end to demodulate the SSB signal.
Test: Single Sideband (SSB) Modulation - Question 4

In the phase shift SSB method to get upper side band

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 4

Concept:

SSB (Single Side Band) modulation is a technique that allows only one sideband to pass saving bandwidth and power both. Practically it is very difficult to pass only a single sideband.

Analysis:

Ex: If we consider a single-tone modulating signal as x(t) = cos ωmt, the SSB modulated wave with only the upper sideband will be represented as:

cos ((ωc + ωm)t) = cos ωc.cos ωmt – sin ωc.sin ωmt

and with lower sideband only will be represented as:

cos (ωc - ωm)t = cos ωct .cos ωmt + sin ωct. sin ωmt

where sin ωmt is the Hilbert transform of the original message signal x(t) = cos ωmt

Conclusion:

Generalizing this for any signal m(t), we can say that the SSB modulated signal with only upper sideband will be:

m(t) cos ωct – m̂(t) sin ωct,

Similarly, we can say that the SSB modulated signal with only lower sideband will be:

m(t) cos ωct + m̂(t) sin ωct,

where m̂(t) is the Hilbert transform of m(t).

SSB/SC is generated using a balanced modulator circuit as shown:

Where π/2 phase shifter gives the Hilbert transform of the incoming signal. 

Test: Single Sideband (SSB) Modulation - Question 5

Which of the following modulation scheme is most bandwidth efficient?

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 5

The bandwidth of different modulation schemes are as shown:

AM → 2fm

SSB-SC → fm

For angle modulated schemes (FM and PM)

= 2(β + 1) fm

fm = message signal bandwidth

So, for SSB-SC, the bandwidth requirement is minimal.

Test: Single Sideband (SSB) Modulation - Question 6

Which of the following circuits could NOT be used as demodulator of SSB?

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 6

Phase Discrimination is used for the demodulation of Frequency Modulate signals.

Additional Information

  • The following methods are used for the demodulation of Single Side Band (SSB) signals.
    • The Filter Method
    • The Phasing Shift Method
    • The Weaver Demodulator
    • Fourier based Demodulation.
  • The following methods are used for the demodulation of Frequency Modulated (FM) signals.
    • ​Frequency discrimination method
    • Phase discrimination method.

​Hence, phase discriminator is used as demodulator of SSB

Test: Single Sideband (SSB) Modulation - Question 7

Direction: Two statements are given. Based on the given information, choose the correct answer.

Statement-I: For the same message signal, the pre-detection SNR is double in the case of conventional practical AM modulation, than that in the case of SSB.

Statement-II: The AM signal bandwidth is double as compared to SSB signal bandwidth.

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 7

Let, the channel is practical having finite attenuation of 'A' dB, and the single-sided noise power spectral density is given as 'N' W/Hz

Let the message signal spectrum is given as:

In the case of AM:-

B.W = 2fm kHz (twice of message signal bandwidth)

In the case of SSB:-

B.W = fm kHz (same as message signal bandwidth)

∴ SNR in the case of S.S.B is double that in the case of AM.

Statement-I is incorrect and Statement-II is correct.

Test: Single Sideband (SSB) Modulation - Question 8

What should be the bandwidth figure of signal to noise ratio for SSB?

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 8

Concept:

SSB (Single Side Band) modulation is a technique that allows only one sideband to pass saving bandwidth and power both.

Practically it is very difficult to pass only a single sideband.

Ex: If we consider a single-tone modulating signal as x(t) = cos ωmt, the SSB modulated wave with only the upper sideband will be represented as:
cos ((ωc + ωm)t) = cos ωc.cos ωmt – sin ωc.sin ωmt

and with lower sideband only will be represented as:

cos (ωc - ωm)t = cos ωct .cos ωmt + sin ωct. sin ωmt

where sin ωmt is the Hilbert transform of the original message signal x(t) = cos ωmt

Generalizing this for any signal m(t), we can say that the SSB modulated signal with only upper sideband will be:
m(t) cos ωct – m̂(t) sin ωct,

Similarly, we can say that the SSB modulated signal with only lower sideband will be:

m(t) cos ωct + m̂(t) sin ωct

where m̂(t) is the Hilbert transform of m(t).

The generalized AM expression is represented as:

s(t) = Ac [1 + μmn (t)] cos ωct

The RF bandwidth of an SSB-AM signal is also 3 kHz. 

Test: Single Sideband (SSB) Modulation - Question 9

The signal m(t) = cos(ωmt) is SSB (single side-band) modulated with a carrier cos(ωct) to get s(t). The signal obtained by passing s(t) through an ideal envelope detector is

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 9

1) General equation of SSB modulated wave:

2) Output of envelope detector to signal

Acos ωct → A

Application:

Equation of SSB modulated signal

Ac = Am = 1

the output of envelope detector = ½

The output of the envelope detector is a constant voltage signal

Hence option (d) which represents a constant voltage is correct.

Test: Single Sideband (SSB) Modulation - Question 10

The modulation technique that takes the lowest bandwidth among the given

Detailed Solution for Test: Single Sideband (SSB) Modulation - Question 10

The modulation technique that takes the lowest bandwidth is SSB-SC

Single Side Band (SSB SC):

1) SSB SC is a form of amplitude modulation where only a single sideband is transmitted and 1 sideband and carrier are suppressed.

2) The advantage of SSB is bandwidth and power-saving over both conventional AM and DSB SC, i.e. DSB SC has a more power consumption than SSB SC.

3) The Bandwidth requirement is only fm, ∴ It needs half the bandwidth than the DSB-SC transmission.

Comparison:

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