Communication Engineering Mock Test

The standard intermediate frequency used for AM receivers is 455 KHz. This frequency is commonly used in AM receivers to convert the received radio frequency signal to a lower frequency that is easier to process and amplify. By using a fixed intermediate frequency, it becomes possible to design and manufacture standardized components for AM receivers, leading to cost efficiency and compatibility among different devices.

Selectivity refers to the ability of a receiver to choose and separate the desired signals from the various incoming signals. It is an important characteristic in communication systems as it allows the receiver to filter out unwanted signals or interference and focus on the signals of interest. A receiver with high selectivity is able to effectively discriminate between different signals and minimize the impact of noise or other unwanted signals, resulting in improved signal quality and overall performance.

In frequency modulation, the amplitude of the carrier signal remains constant. Frequency modulation involves varying the frequency of the carrier signal in accordance with the modulating signal. This means that the amplitude of the carrier signal does not change, only its frequency. Therefore, in the case of frequency modulation, the amplitude is constant.

Bandwidth refers to the amount of data that can be transmitted within a given time frame. It represents the capacity or speed of data transmission. Therefore, the correct answer is Bandwidth. Frequency, Noise, and Signal power are not directly related to the amount of data transmitted but rather represent different aspects of data transmission or characteristics of a signal.

FSK reception can be both phase coherent and phase non-coherent. Phase coherence refers to the ability of the receiver to accurately track and synchronize with the phase of the incoming signal. In phase coherent FSK reception, the receiver maintains phase coherence with the incoming signal, allowing for accurate demodulation and decoding of the FSK signal. On the other hand, phase non-coherent FSK reception does not require phase synchronization and can still demodulate the FSK signal by detecting frequency changes. Therefore, FSK reception can be both phase coherent and phase non-coherent depending on the specific implementation and requirements.

The modulation index of a frequency modulated (FM) signal is calculated by dividing the frequency deviation by the modulating frequency. In this case, the frequency deviation is given as 50 KHz and the modulating frequency is 10 KHz. Therefore, the modulation index is 50/10 = 5.

The modulation index is calculated by taking the average of the modulation indices of the individual modulating signals. In this case, the three modulating signals have modulation indices of 0.6, 0.3, and 0.4. Taking the average of these values gives us (0.6 + 0.3 + 0.4)/3 = 0.433. Therefore, the correct answer is 0.433.

In Amplitude Modulation (AM), the total power of the signal is given by the formula Ptotal = (1 + m^2/2) * Pcarrier, where Pcarrier is the power of the carrier signal and m is the modulation index. In this case, the carrier power is 800 W and the modulation index is 50 percent (0.5). Plugging these values into the formula, we get Ptotal = (1 + 0.5^2/2) * 800 = 1.25 * 800 = 1000 W. Therefore, the correct answer is 900 W.

On-off keying (OOK) is typically associated with binary modulation techniques where the presence of a carrier signal represents one binary state (typically "1") and the absence of the carrier signal represents the other binary state (typically "0").

Among the options provided, "None of the mentioned" would be the correct choice. While On-off keying is a form of modulation, it is distinct from both Amplitude Shift Keying (ASK) and Uni-polar Pulse Amplitude Modulation (PAM).

FSK (Frequency Shift Keying) reception is a method of transmitting digital information by varying the frequency of the carrier signal. In order to demodulate the FSK signal, a receiver is required. The receiver typically uses a combination of a correlation receiver and a PLL (Phase-Locked Loop). The correlation receiver helps in detecting the frequency shift in the received signal, while the PLL helps in tracking and synchronizing the carrier frequency. Therefore, the correct answer is "Correlation receiver & PLL".

In BPSK (Binary Phase Shift Keying), the symbols 1 and 0 are denoted by a carrier wave with a phase shift of π. This means that when the symbol 1 is transmitted, the carrier wave is shifted by π radians, and when the symbol 0 is transmitted, there is no phase shift. This phase shift allows for the transmission of binary data over a communication channel.

Digital modulation refers to the process of changing the characteristics of a sinusoidal carrier signal with respect to a digital input signal. This is done by modifying the carrier signal's amplitude, frequency, or phase to represent the digital data. Analog modulation, on the other hand, involves changing the characteristics of the carrier signal with respect to an analog input signal. Encoding is the process of converting data into a specific format for transmission or storage. Demodulation is the process of extracting the original signal from a modulated carrier signal. Therefore, the correct answer is Digital Modulation.

ASK (Amplitude Shift Keying) is most affected by noise because it uses changes in the amplitude of the carrier signal to transmit data. Noise can cause fluctuations in the amplitude, leading to errors in the received signal. In contrast, PSK (Phase Shift Keying) and FSK (Frequency Shift Keying) are more resilient to noise because they rely on changes in phase and frequency, respectively, which are less susceptible to distortion. QAM (Quadrature Amplitude Modulation) combines both amplitude and phase modulation, so it is also affected by noise, but to a lesser extent compared to ASK.

The noise is generally developed in the RF stage of radio type receivers. The RF stage is responsible for receiving the radio frequency signals from the antenna and amplifying them before further processing. During this amplification process, noise can be introduced and mixed with the desired signal, resulting in a degraded signal-to-noise ratio. Therefore, the RF stage is a critical stage where noise is typically generated in radio receivers.

SSB (Single Sideband) modulation technique uses the minimum channel bandwidth and transmitted power compared to other modulation techniques like FM, DSB-SC, and VSB. In SSB, only one sideband is transmitted along with the carrier signal, while the other sideband and the carrier are suppressed. This reduces the bandwidth requirement and power consumption, making SSB more efficient in terms of spectrum utilization. Therefore, SSB is the correct answer for the modulation technique that uses the minimum channel bandwidth and transmitted power.

Narrow Band FM refers to a type of frequency modulation where the frequency sensitivity (kf) is small and the bandwidth is narrow. This means that small changes in the modulating signal will result in small changes in the carrier frequency, and the range of frequencies occupied by the modulated signal is relatively narrow. This characteristic is useful in applications where a narrow range of frequencies needs to be transmitted or received, such as in certain types of radio communication or audio transmission.

The image frequency for a standard broadcast AM superheterodyne receiver tuned to a station at 700 kHz is 1610 kHz. In a superheterodyne receiver, the incoming radio frequency is mixed with a local oscillator frequency to produce an intermediate frequency (IF) signal. The image frequency is a potential interference signal that is produced when the incoming frequency is mixed with a harmonic of the local oscillator frequency. In this case, the image frequency is 1610 kHz, which is the result of mixing 700 kHz with a harmonic of the local oscillator frequency.

The minimum bandwidth to send an information without loss is called Nyquist Bandwidth. This concept is based on the Nyquist-Shannon sampling theorem, which states that in order to accurately reconstruct a signal, the sampling rate must be at least twice the highest frequency component of the signal. Nyquist Bandwidth refers to the minimum bandwidth required to transmit a signal without any loss of information during the process. It is named after Harry Nyquist, who made significant contributions to the field of telecommunications.

Carson's rule states that the bandwidth of FM can be approximated by twice the sum of the modulating frequency and the maximum frequency deviation. In this case, the modulating signal is 2 KHZ and the maximum frequency deviation is 12 KHZ. Therefore, the bandwidth can be calculated as 2 * (2 KHZ + 12 KHZ) = 28 KHZ.

In an amplitude modulated wave, the carrier signal carries the majority power from the transmitter to the receiver. The carrier signal is a high-frequency signal that is modulated by the lower-frequency message signal. The carrier wave remains unchanged in terms of frequency and amplitude, but its power is used to transmit the modulated message signal. Therefore, the correct answer is "Carrier".

Lower frequency is not suitable in direct transmission because lower frequencies have longer wavelengths, which results in poorer signal propagation and higher susceptibility to interference. Higher frequencies, on the other hand, have shorter wavelengths and are better suited for direct transmission as they can carry more data and have better signal quality.

The A/D converter is not an incorrect choice in an analog communication system. It is a crucial component that converts analog signals into digital form for processing and transmission. This conversion allows for better signal quality and noise reduction in digital communication systems. Therefore, the correct answer is not the A/D converter.

The carrier current in the antenna can be calculated by dividing the total antenna current by the modulation index. In this case, the total antenna current is 10A and the modulation index is 0.8. Therefore, the carrier current in the antenna is 10A / 0.8 = 12.5A. However, none of the given options match this calculation, so the correct answer is not available.

The bandwidth of a multitone amplitude modulation system is determined by the highest frequency in the modulation signal. In this case, the modulating frequencies are 2 kHz and 5 kHz. The highest frequency is 5 kHz, so the bandwidth is 5 kHz. Therefore, the correct answer is 10 kHz.

FM is disadvantageous over AM signal because it requires a much wider channel bandwidth. This means that FM signals occupy a larger portion of the frequency spectrum, limiting the number of channels that can be accommodated. Additionally, FM systems are more complex and costlier to implement compared to AM systems. The complexity arises from the need for more sophisticated modulation and demodulation techniques. Furthermore, FM signals are more susceptible to adjacent channel interference, which can degrade the quality of the received signal.

The incorrect statement regarding the disadvantage of TRF receiver is "Not capable of receiving and detecting weak RF signals". TRF receivers are actually capable of receiving and detecting weak RF signals.

The degree of modulation depends on the amplitude of both the carrier and the modulating wave. Modulation refers to the process of varying the amplitude, frequency, or phase of a carrier wave in accordance with the information signal (modulating wave) to be transmitted. In amplitude modulation (AM), the amplitude of the carrier wave is modulated by the amplitude of the modulating wave. Therefore, the degree of modulation, which represents the extent to which the carrier wave is modulated, is determined by the amplitudes of both the carrier and the modulating wave.

The modulated signal in AM broadcasting should be 0.8 MHz in order for the height of the antenna to be 90m. This is because the height of the antenna is not directly related to the frequency of the modulated signal. The height of the antenna is determined by other factors such as the wavelength of the signal and the desired coverage area.

Super heterodyne receivers have better sensitivity because they use a local oscillator to convert the incoming signal to a fixed intermediate frequency (IF), which amplifies the signal and improves its overall sensitivity. They also have high selectivity because they use a narrow bandpass filter at the IF stage, allowing only the desired frequency to pass through and rejecting other frequencies. However, they require extra circuitry for frequency conversion, as the incoming signal needs to be mixed with the local oscillator signal to produce the IF signal.

In the case of radio transmission, the source of transmission is space. Radio waves are electromagnetic waves that travel through space from the transmitter to the receiver. They do not require any physical medium, such as cables or coaxial connections, to transmit the signal. The antenna is used to capture and emit these radio waves, allowing for the transmission of information wirelessly through space.