Modulation and Detection MCQ Quiz in తెలుగు - Objective Question with Answer for Modulation and Detection - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

• Vestigial type modulation gives low bandwidth
• It is called asymmetric sideband system which is compromise SSB (signal sideband) and DSBSC (double sideband suppressed carrier) modulation
• It is used in TV for transmission of the picture signal 

Concept:

According to Carson rule signal, BW is given as:

B.W = (β + 1) 2fm

\(\becauseβ=\frac{Δf}{f_m} \)

B.W. = 2[Δf + fm]          

If multiple frequencies are available in modulating signal then,

B.W. = 2(β + 1) fmax 

Calculation:

In FM modulation the modulation index β = Δf/f

f = modulating frequency = 75 kHz for standard FM broadcast

The correct answer is Convert analog signals to digital and vice-versa

• The modem is a device that transforms computer-generated digital signals into analog signals to enable their traveling through phone lines. The ‘modulator-demodulator’ or modem may work as a dial-up for LAN or connect to an ISP.
• Modems can be both external, as in the device which connects to the USB or the serial port of a computer machine, or proprietary components for handheld smart devices and other devices, also as internal, in the form of add-on expansion cards for computer systems and PCMCIA cards for laptop computers.

Key Points

• The design of a modem differs for both the external and internal modem. In internal modems, IRQ – Interrupt request is utilized to configure the modem in addition to I/O, which is a memory address. Usually, before the installation of a built-in modem, integrated serial interfaces are disabled, assigning them the COM2 resources at the same time.
• For external types of a modem, the modem assigns and uses the resources itself. This is especially helpful for USB port and laptop users as the non-complex and simpler nature of the process render it far more useful for daily usage.

• At the time of setup, the second step to make sure the proper working of a modem is the installation of drivers. The modem working efficiency and processing is decided by two factors:

• Speed of UART –An acronym for Universal Asynchronous Receiver or Transmitter chip(installed on the motherboard to which the modem connection is established)
• Speed of the modem itself

Frequency modulation is most widely used in radio transmission. In it, the frequency of the carrier signal is changed according to a change in message signal.

A simple AM detector uses a diode to get a positive or negative envelope of AM  modulated signal and a capacitor acting as low pass filter to filter out RF signals producing the modulated audio signal at the output.

Explanation:

Amplitude Limiter in FM Receivers

Definition: An amplitude limiter is a circuit found in frequency modulation (FM) receivers that is used to remove amplitude variations in the received signal. These amplitude variations are often caused by noise and interference. The primary purpose of the amplitude limiter is to maintain a consistent amplitude level of the FM signal before it is demodulated, ensuring that the signal's frequency variations, which carry the information, are preserved without being affected by amplitude noise.

Working Principle: In an FM receiver, the amplitude limiter operates by clipping the peaks of the incoming signal. This clipping process effectively removes any amplitude variations that exceed a certain threshold, which is set to be just above the maximum amplitude of the desired signal. By doing so, the amplitude limiter ensures that the output signal has a constant amplitude, which is crucial for the proper demodulation of the FM signal. The frequency variations of the signal, which contain the actual information, remain intact and unaffected by the amplitude limiting process.

Advantages:

• Improves the signal-to-noise ratio (SNR) by eliminating unwanted amplitude variations caused by noise.
• Prevents overloading of subsequent stages in the receiver, such as the demodulator, by maintaining a consistent signal amplitude.
• Enhances the overall performance and reliability of the FM receiver by ensuring that the demodulated signal accurately represents the original transmitted information.

Disadvantages:

• May introduce distortion if the threshold for amplitude limiting is not set correctly.
• Can potentially clip desired signal components if the signal experiences rapid and significant amplitude variations.

Applications: Amplitude limiters are commonly used in various types of FM receivers, including those found in radio broadcasting, two-way communication systems (such as walkie-talkies), and other wireless communication devices that utilize frequency modulation.

Correct Option Analysis:

The correct option is:

Option 1: Remove amplitude variations due to noise.

This option accurately describes the primary function of an amplitude limiter in FM receivers. By removing amplitude variations caused by noise, the amplitude limiter ensures that the signal's amplitude remains constant, allowing for accurate demodulation of the frequency variations that carry the information.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Filtration.

This option is incorrect because filtration refers to the process of removing specific frequency components from a signal, typically using filters. While filtration is an important aspect of signal processing in FM receivers, it is not the primary function of an amplitude limiter.

Option 3: Demodulation.

This option is incorrect because demodulation is the process of extracting the original information signal from the modulated carrier wave. Although demodulation is a critical function in FM receivers, it is not the role of the amplitude limiter. The amplitude limiter prepares the signal for demodulation by removing amplitude variations, but it does not perform the demodulation itself.

Option 4: Amplification.

This option is incorrect because amplification refers to increasing the amplitude of a signal. While amplification is necessary in FM receivers to boost the signal strength, it is not the function of an amplitude limiter. The amplitude limiter, in fact, works to keep the amplitude constant rather than increasing it.

Conclusion:

Understanding the role of an amplitude limiter in FM receivers is essential for appreciating its importance in maintaining signal integrity. By removing amplitude variations caused by noise, the amplitude limiter ensures that the frequency variations, which carry the information, are accurately demodulated. This function significantly enhances the performance and reliability of FM receivers, making amplitude limiters a crucial component in modern communication systems.

Basic principles of producing moving pictures are based on the Illusion of Continuity

It’s necessary to present the picture to the eye in such a way that an illusion of continuity is created and any motion in the sense appears on the picture tube screen as a smooth and continuous change

• To achieve this it should follow the persistence of vision or storage characteristics of the human eye.
• The sensation produced when the nerves of the eye’s retina and stimulated by an incident light does not cease immediately after the light is removed but persists for about \(\frac{1}{{16}}{\rm{th}}\) of a second.
• If the scanning rate per second is made greater than the 16 or number of pictures shown per second is more than 16, the eye is able to integrate the change of brightness.
• Each picture of the frame is projected individually as a still picture, but they are shown one after another in a rapid manner to produce the illusion of continuity in the motion pictures.
• In the present day, 24 frames per one second are transmitted at the same rate in motion pictures in order to make an ‘illusion of image continuity’. 

• In frequency modulation, the frequency of the carrier signal is changed according to a change in the message signal.
• For an unmodulated signal, the message signal is zero, so the output of the FM detector which detects a change in frequency will be zero.