Lab 4: SIMULINK Exp

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Questions and Answers

What does the term kf represent in FM signals?

Phase sensitivity in degrees
Modulation index
Amplitude of the carrier signal
Frequency sensitivity in Hertz per unit of m(t) (correct)

The modulation index of an FM signal is determined by which of the following parameters?

Carrier frequency and phase angle
Frequency sensitivity and phase shift
Frequency deviation and frequency of the modulating signal (correct)
Amplitude of the modulating signal and amplitude of the carrier signal

What is the equation for frequency deviation Δf in FM?

$\, Δf = kf Am$ (correct)
$\, Δf = A_m kf$
$\, Δf = A m cos(2πfm t)$
$\, Δf = kf + Am$

Which statement regarding the instantaneous frequency fi(t) of the FM signal is correct?

fi(t) fluctuates based on kf and m(t) (A) Signup and view all the answers

Which factor does NOT influence the bandwidth of an FM signal?

Total time duration of transmission (C) Signup and view all the answers

Which of the following describes the effect of peak-to-peak voltage on frequency deviation in FM?

Higher peak-to-peak voltage increases frequency deviation (D) Signup and view all the answers

What is the relationship between the amplitude spectrum of FM signals and sideband frequencies?

The sidebands are dependent on the modulation index (B) Signup and view all the answers

How often does a carrier frequency oscillate at a frequency of 10 kHz?

10,000 times per second (C) Signup and view all the answers

What does the modulation index in FM modulation represent?

The ratio of the maximum frequency deviation to the maximum message frequency (C) Signup and view all the answers

What is the significance of Bessel functions in FM modulation?

They describe the amplitude of the spectral components (A) Signup and view all the answers

In the frequency domain representation of FM signals, what do the sidebands represent?

Frequency components surrounding the carrier frequency (A) Signup and view all the answers

How does the value of Jn(β) change with increasing n?

It decreases and approaches zero for large values of n (B) Signup and view all the answers

What happens to the spectral lines as the modulation index increases?

The relative amplitudes of the spectral lines vary based on Jn(β) (B) Signup and view all the answers

Which equation correctly represents the FM modulated signal for a non-sinusoidal message?

x(t) = A cos(2πfCt + β sin(2πft)) (C) Signup and view all the answers

What is indicated by the term 'fc ± nfm' in the sideband analysis of FM signals?

The range of frequencies around the carrier frequency (B) Signup and view all the answers

What does the bandwidth W represent in the context of the modulation index?

The range of frequencies of the message signal (A) Signup and view all the answers

What is the effect of increasing the modulation index β greater than 1 in FM signals?

More sideband lines are produced. (C) Signup and view all the answers

How are the different message signals separated in Frequency Division Multiplexing (FDM) at the receiver?

Through the use of a bandpass filter. (C) Signup and view all the answers

In the context of FM signals, what allows for a clear distinction between modulated signals in the frequency domain?

The introduction of guard bands. (A) Signup and view all the answers

What is the primary role of Bessel functions in FM modulation?

They describe the amplitude distribution of sidebands. (A) Signup and view all the answers

When examining the amplitude spectrum of FM signals, what happens to the amplitude when the modulation index β is low?

Fewer distinct spectral lines are visible. (C) Signup and view all the answers

Which multiplexing technique modulates different signals at different carrier frequencies?

Frequency Division Multiplexing (FDM) (B) Signup and view all the answers

What happens to the sideband lines in an FM signal if the modulation index β is set to a very high value?

Many sideband lines with appreciable amplitude will appear. (D) Signup and view all the answers

What is the primary benefit of using multiplexing in communication systems?

Efficient utilization of channel bandwidth. (B) Signup and view all the answers

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Study Notes

Frequency Modulation (FM)

Frequency sensitivity of an FM signal, denoted as kf, is measured in Hertz per unit of m(t).
Instantaneous frequency of an FM signal, fi(t), is the sum of the carrier frequency fc and the product of the frequency sensitivity kf and the modulating signal m(t).
Maximum change in instantaneous frequency fi from the carrier frequency fc is called frequency deviation, denoted as Δf, and is given by: Δf = kf Am.
Frequency deviation is used to determine the bandwidth of FM signals.
Modulation index, denoted as β, quantifies the deviation of the instantaneous frequency from the carrier frequency, and is given by: β = kf Am / fm.
For a non-sinusoidal signal, the modulation index is given by: β = kf m(t)max / W, where W is the bandwidth of the message signal.
In the frequency domain, the spectrum of an FM signal consists of a carrier-frequency component and an infinite number of sideband components at frequencies fc  nfm (n = 1,2,3,4,5…..).
The amplitude of spectral lines is determined by the Bessel function Jn().
Number of significant spectral lines depends on the modulation index β.
As β increases, there will be more sideband lines.

Frequency Division Multiplexing (FDM)

Multiplexing allows multiple signals to be transmitted simultaneously over a single channel.
In FDM, different message signals are modulated at distinct carrier frequencies.
Modulated signals are combined into a composite signal and transmitted over the shared medium.
Guard bands separate modulated signals to prevent interference.
At the receiver, bandpass filters separate the modulated signals from the composite signal.
Demultiplexing recovers the individual message signals from the modulated signals.
Low pass filters remove any unwanted high-frequency components to recover the message signals.

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