Amplitude Modulation MCQ Quiz in मल्याळम - Objective Question with Answer for Amplitude Modulation - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

• For μ < 1, the AM wave is said to be under modulated.
• For μ > 1, the AM wave is said to be over modulated.
• For μ = 1, the AM wave is said to be critically modulated.
• 100% modulation is where the modulating signal drives the carrier to zero and is theoretically the maximum modulation that can be successfully demodulator by a regular AM envelope detector.

A general Amplitude modulation process is as shown:

Concept:

Power of a transmitted AM wave is given as:

\(P_t = {P_c}\left( {1 + \frac{{{μ ^2}}}{2}} \right)\)

\(P_t = {P_c} + P_c\frac{μ ^2}{2}\)

Power in the carrier = Pc

Power in both the sidebands is given by:

\(P_s= \frac{{{P_c}{μ^2}}}{2}\)

Since the power is distributed equally to the left and to the right side of the sideband, the power in one of the sidebands is given by:

\(P_{s1}= \frac{{{P_c}{u^2}}}{4}\)

Analysis:

We know that:

 \({P_t} = {P_c}\left( {1 + \frac{{{\mu ^2}}}{2}} \right)\)

\(2.09 = {P_c}\left( {1 + \frac{{0.09}}{2}} \right)\)

\(\therefore {P_c} = 2\;Watts\)

Power in each sideband is:

 \({P_{SB}} = {P_c}~\frac{{{\mu ^2}}}{4} = \frac{{2\left( {0.09} \right)}}{4}\)

\( = 0.045\;Watts\)

Explanation:

In AM modulation Index is defined as:

\(μ = \frac{{{A_m}}}{{{A_c}}} = \frac{{{A_{max}} - {A_{min}}}}{{{A_{max}} + {A_{min}}}}\)

Where Am = amplitude of modulating wave

Ac = amplitude of carrier wave

Clearly, it is independent of fm.

• The value of modulation varies from 0 to 1.   0 ≤ μ ≤ 1
• For μ < 1, the AM wave is said to be under modulated.
• For μ > 1, the AM wave is said to be over-modulated.
• For μ = 1, the AM wave is said to be critically modulated.
• 100% modulation is where the modulating signal drives the carrier to zero and is theoretically the maximum modulation that can be successfully demodulator by a regular AM envelope detector.

A general Amplitude modulation process is as shown:

Concept:

The general amplitude modulated signal expression is:

 \({\rm{s}}\left( {\rm{t}} \right) = {{\rm{A}}_{\rm{c}}}\left( {1 + {\rm{\mu }}\cos {{\rm{\omega }}_{\rm{m}}}{\rm{t}}} \right)\cos {{\rm{\omega }}_{\rm{c}}}{\rm{t}}\)

A single tone modulated signal is given as:

Maximum envelope: Ac (1+μ)

Minimum envelope: Ac (1-μ)

Where Ac is the carrier amplitude and μ is the modulation index.

\(P_c= \frac{{A_c^2}}{2}\)

The total power of an amplitude-modulated signal is given by:

\(P_t = P_c\;\left( {1 + \frac{{{\mu ^2}}}{2}} \right)\)

Sideband power = Total power – Carrier power

\(Efficiency = \frac{{Sideband\;power}}{{Total\;power}}\)

Analysis:

X_AM(t) = [A + 0.3 A cos ω_mt] cos ω_c t

= A [1 + 0.3 cos ω_mt] cos ω_c t

By comparing with the standard equation

μ → 0.3

Power efficiency 

= \(\frac{{\frac{{{P_c}\;{\mu ^2}}}{2}}}{{{P_c}\left( {1 + \frac{{{\mu ^2}}}{2}} \right)}}\)

= \(\frac{{{\mu ^2}}}{{{\mu ^2} + 2}}\)

= \(\frac{{{{\left( {0.3} \right)}^2}}}{{{{\left( {0.3} \right)}^2} + 2}}\)

= 0.04306

% power efficiency = 0.04306 × 100

= 4.306%

A scheme in which several channels are interleaved and then transmitted together is known as Frequency division multiplexing.

In Frequency division multiplexing signals occupy a range of frequency and two adjacent signals are separated by guard band to prevent mixing.

All the multiplexed signals are then transmitted simultaneously

Concept:-

For SSB the output SNR is:-

\(\frac{{{S_0}}}{{{N_0}}} = \frac{{{S_i}}}{{\eta {f_m}}}\)

Calculation:-

Given,

 \(\frac{\eta }{2} = {10^{ - 9}}\;W/Hz\)

f_m = 10 kHz

Channel loss = 20 dB

\(\frac{{{S_i}}}{{n{f_m}}} = 40\;dB = {10^4}\)

∴ S_i = 10⁴ × 10^-9 × 2 × 10 × 10³

= 0.2 W

Required minimum signal strength at the receiver input

S_i = 0.2 W

Required minimum signal strength at the transmitter output:-

S_i × 20 dB = 0.2 × 10² = 20 W

Important note:-

For DBS-C, signal energy available in sideband = \(\frac{{{S_i}}}{3}\)

Then, required minimum output SNR

= \(\frac{{\frac{{{S_i}}}{3}}}{{\eta {f_m}}}\)

In AM broadcasting, vertical polarization is employed because of:

(i) Absorption of the wave of a negligible chance due to physical obstacles or environmental

conditions

(ii) The alignment of the Antenna is vertical generally.

So option (4) is correct.

Important Points:

The polarization of a wave is an orientation of the electric-field line during wave propagation.

Generally, Polarization has three kinds:

• AM signals are polarized, as shown by the directional response of an AM radio to a radio signal.
• When it is aligned with the magnetic component of radio waves, the internal-loop antenna picks up the signal, but when it is at right angles, it doesn't.
• Vertical AM transmitting antennae broadcast vertically polarized radio waves (electric field has a vertical orientation).

The ring modulator and balanced modulator is generally used for the modulation of DSB SC signal.

SSB/SC is generated using a balanced modulator

Concept:

A single tone modulated signal is given as:

Maximum envelope Amax : Ac (1+μ)

Minimum envelope Amin : Ac (1-μ)

\(\frac{{{A_{max}}}}{{{A_{min}}}} = \frac{{1 + μ}}{{1 - μ}}\)

The above can be written as:

\(μ = \frac{{{A_{max}} - {A_{min}}}}{{{A_{max}} + {A_{min}}}}\)

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: