Electronic Engineering: Radio Transmission Test

Selectivity refers to the ability of a receiver to identify and pick the desired signal from other signals present in the frequency spectrum. It is a measure of how well a receiver can reject unwanted signals and only select the desired signal. A high selectivity means that the receiver can effectively filter out interference and noise, allowing for clear and accurate signal reception.

The diode detector is the simplest AM detector because it only requires a single diode to rectify the modulated signal and extract the audio information. It works by allowing the positive half of the signal to pass through while blocking the negative half, resulting in a pulsating DC signal that can be filtered to obtain the original audio. The other options mentioned (product detector, synchronous detector, and heterodyne detector) are more complex and involve additional circuitry or techniques to improve performance or eliminate unwanted interference.

Linear amplifiers are designed to amplify the input signal by a constant factor, making the output signal an enlarged replica of the input. Unlike switching amplifiers that operate in discrete on/off states or tuning amplifiers that are used for selective frequency amplification, linear amplifiers provide a continuous and proportional output. Operational amplifiers, on the other hand, are versatile amplifiers that can perform various mathematical operations on the input signal, but they may not necessarily provide an identical, enlarges replica of the input.

A Colpits oscillator uses a tapped capacitor. In this type of oscillator, the capacitor is connected in parallel with the inductor, forming a tank circuit. The tapping point on the capacitor allows for feedback to be provided to the transistor or active device in the circuit. This feedback is necessary for sustaining oscillations. By adjusting the tapping point on the capacitor, the frequency of oscillation can be controlled.

A spectrum analyzer is an instrument that displays the amplitude versus frequency on a CRT (Cathode Ray Tube) screen. This means that it allows the user to visualize the different frequencies present in a signal and their corresponding amplitudes. It is commonly used to analyze and measure the frequency content of electrical or electromagnetic signals. By observing the spectrum displayed on the CRT, it can be determined if a transmitter's output signal is free from any unwanted or spurious signals. Therefore, the correct answer is that a spectrum analyzer is an instrument that displays amplitude versus frequency on CRT.

The sensitivity of the FM receiver can be calculated by subtracting the limiter's quieting voltage from the voltage gain. In this case, the voltage gain is 113 dB, which is equivalent to a gain of 10^(113/20) = 1.9953 x 10^11. Subtracting the limiter's quieting voltage of 400mV (or 0.4V) from the voltage gain gives us 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11 - 0.4 = 1.9953 x 10^11

A buffer amplifier is a circuit that isolates the carrier oscillator from load changes. It is designed to prevent any changes in the load from affecting the performance and stability of the carrier oscillator. The buffer amplifier provides a high input impedance and a low output impedance, allowing it to effectively isolate the oscillator from any variations in the load. This helps to maintain a consistent signal quality and prevent any distortion or degradation caused by load changes.

If the microphone of an FM transmitter fails to work, it means that no audio signal is being received or transmitted. In FM modulation, the audio signal is used to vary the frequency of the carrier wave. Without the audio signal, the carrier wave remains unmodulated, meaning that its frequency remains constant. Therefore, the correct answer is an unmodulated carrier.

Class B power amplifiers are commonly used in push-pull amplifiers. In a push-pull configuration, two transistors or tubes are used to amplify the positive and negative halves of the input signal, respectively. Class B amplifiers are known for their efficiency, as each transistor or tube only conducts during one half of the input waveform, reducing power consumption. This type of amplifier is commonly used in audio applications where high power output is required, such as in audio amplifiers for speakers.

In a Hartley oscillator, a positive feedback is coupled to the input through a tapped coil. This means that a portion of the output signal is fed back to the input through a coil that has a tap or a connection point along its windings. This tapped coil allows the oscillator to generate the desired oscillations by creating a feedback loop that reinforces the input signal. By tapping the coil at a specific point, the feedback can be precisely controlled, ensuring the oscillator operates at the desired frequency.

The shape factor of a receiver is defined as the ratio of its 60 dB bandwidth to its 6 dB bandwidth. In this case, the 60 dB bandwidth is given as 12 kHz and the 6 dB bandwidth is given as 3 kHz. Therefore, the shape factor can be calculated as 12 kHz divided by 3 kHz, which equals 4.

CDMA stands for code division multiple access system. This technology allows multiple users to share the same frequency band simultaneously by assigning a unique code to each user. This code is used to separate and differentiate the signals of different users, enabling them to transmit and receive data simultaneously without interference. CDMA is widely used in telecommunications, particularly in mobile communication systems, due to its efficiency in utilizing the available bandwidth and its ability to provide secure and reliable communication.

The FM broadcast band occupies 7.4% of the VHF band.

Carson's rule states that the bandwidth of an FM signal is equal to twice the sum of the frequency deviation and the highest modulating frequency. In this case, the frequency deviation is given as 100 kHz and the modulating index is 5. Therefore, the highest modulating frequency can be calculated by dividing the frequency deviation by the modulating index, which gives 20 kHz. Adding this to the frequency deviation, we get 120 kHz. Multiplying this by 2 gives us the bandwidth of 240 kHz.

FM broadcasting uses Frequency Division Multiplexing (FDM) as its multiplexing scheme. FDM allows multiple signals or channels to be transmitted simultaneously over a single communication medium by dividing the available frequency spectrum into smaller frequency bands. Each channel is assigned a different frequency band, and the signals are combined and transmitted together. In the case of FM broadcasting, different radio stations are allocated specific frequency bands within the FM radio spectrum, allowing them to transmit their signals without interference.

When the voltage is doubled, the corresponding change in dB can be calculated using the formula: dB = 20 * log10(V2/V1), where V1 is the original voltage and V2 is the new voltage. Since the voltage is equal to twice its original value, V2/V1 = 2/1 = 2. Substituting this value into the formula, we get dB = 20 * log10(2) = 20 * 0.301 = 6 dB. Therefore, the corresponding change in dB is 6 dB.

Double conversion is used to overcome the problem of image frequency. Image frequency refers to the interference or distortion caused by the presence of unwanted frequencies that are close to the desired frequency. By using a double conversion process, the incoming signal is first converted to a higher frequency and then downconverted to the desired frequency. This helps in filtering out the unwanted frequencies and reducing the impact of image frequency interference, resulting in a cleaner and more accurate signal.

Time-division multiplexing is a technique used to transmit multiple signals over a single communication channel by dividing the available time into multiple time slots. Each signal is assigned a specific time slot, and they are transmitted sequentially. This method is commonly used in digital transmission systems to efficiently utilize the available bandwidth and ensure accurate synchronization of the signals. Therefore, the correct answer is digital transmission.

The sensitivity of a receiver refers to its ability to pick up weak signals or stations. It indicates how well the receiver can detect and amplify low-power signals, allowing it to receive weak stations that might be difficult to pick up with less sensitive receivers. Therefore, the correct answer is "receive weak stations."

An SSB (Single Sideband) phone signal can be generated by using a balanced modulator followed by a mixer. A balanced modulator is used to suppress one of the sidebands and the carrier, resulting in a single sideband signal. The mixer then combines this single sideband signal with a local oscillator signal to generate the final SSB phone signal. This method allows for efficient use of bandwidth and reduces the transmission power required.

The approximate wavelength of violet light is 7000 angstroms. Wavelength is a measure of the distance between two consecutive peaks or troughs of a wave. Violet light has a shorter wavelength compared to other visible colors, such as red or blue. The wavelength of light is typically measured in units of angstroms, where 1 angstrom is equal to 0.1 nanometers. Therefore, 7000 angstroms is a reasonable approximation for the wavelength of violet light.

The piezoelectric effect refers to the mechanical vibration of a crystal when voltage is applied to it. When an electric field is applied to certain crystals, such as quartz or tourmaline, they undergo mechanical deformation and produce vibrations. This effect is utilized in various applications, such as in piezoelectric sensors and actuators, where the mechanical vibrations can be converted into electrical signals or vice versa.

A radio transmitter is a device that takes information to be communicated and converts it into an electronic signal compatible with the communication medium. It is responsible for transmitting the signal over the airwaves to be received by a radio receiver. The transmitter modulates the information onto a carrier wave, allowing it to be transmitted wirelessly. Therefore, a radio transmitter is the correct answer in this case.

Demodulation is the process of extracting the original intelligence signals from a carrier wave after it has been received at the receiver station. In this process, the lower frequency intelligence signals are separated from the transmission frequency, allowing them to be further processed or utilized. Demodulation is an essential step in wireless communication systems as it allows for the recovery of the transmitted information.

The tuned circuit prior to the mixer in a superheterodyne receiver is called the preselector. This circuit is responsible for selecting the desired frequency and filtering out unwanted frequencies before they reach the mixer. The preselector helps to improve the receiver's sensitivity and selectivity by allowing only the desired frequency to pass through. The front end and tuner are also components of the receiver, but they may refer to a broader range of circuits and functions. Therefore, the correct answer is preselector.

The input signal into a PLL is the phase detector. The phase detector is responsible for comparing the phase of the input signal with the phase of the reference signal. It generates an error signal based on the phase difference between the two signals. This error signal is then used to control the VCO (Voltage Controlled Oscillator) to adjust its frequency and phase to match that of the reference signal. Thus, the phase detector plays a crucial role in the operation of a PLL by continuously comparing and adjusting the phase of the input signal.

The baseband frequency is the source of sidebands in frequency modulation. In frequency modulation, the carrier signal's frequency is varied in proportion to the baseband signal. This modulation process creates sidebands, which are additional frequencies that are symmetrically spaced around the carrier frequency. The amplitude and position of these sidebands are determined by the characteristics of the baseband signal. Therefore, the baseband frequency is the source of these sidebands in frequency modulation.

The standard AM radio broadcast band is in the MF (Medium Frequency) range. This frequency band typically ranges from 535 to 1605 kilohertz (kHz). AM radio stations use MF frequencies to transmit their signals, which can travel long distances due to their ability to bounce off the ionosphere. VHF (Very High Frequency), HF (High Frequency), and UHF (Ultra High Frequency) are not the correct frequency bands for standard AM radio broadcasts.

The overall S/N ratio of the circuits connected in tandem can be found by adding the individual S/N ratios. Since each circuit has an S/N ratio of 30 dB, adding them together gives a total of 120 dB. However, since the S/N ratio is measured in decibels, it is a logarithmic scale and should be converted back to a linear scale before adding. Converting 30 dB to a linear scale gives a ratio of 1000:1. Adding the ratios of the four circuits together gives a total ratio of 1000 x 1000 x 1000 x 1000:1, which is equal to 1000^4:1. Converting this back to decibels gives a total S/N ratio of 40 dB. Therefore, the correct answer is 24 dB.

The equivalent noise temperature of a satellite can be calculated using the formula T = (F - 1) * To, where T is the equivalent noise temperature, F is the noise figure, and To is the reference temperature (usually 290 K). In this case, the noise figure is given as 1.6 dB, which is equivalent to 1.6 dB = 10*log(F), where F is the noise figure. Solving for F, we get F = 10^(1.6/10) = 3.981. Plugging this value into the formula, we get T = (3.981 - 1) * 290 K = 2.981 * 290 K = 864.59 K. Since the closest option is 129 K, that is the correct answer.

The modulation percentage is calculated by taking the difference between the maximum and minimum values of the AM waveform and dividing it by the sum of the maximum and minimum values, then multiplying by 100. In this case, the difference between the maximum and minimum values is 100 V - 40 V = 60 V. The sum of the maximum and minimum values is 100 V + 40 V = 140 V. Dividing 60 V by 140 V and multiplying by 100 gives a modulation percentage of 42.86%. Since none of the given answer options match exactly, the closest option is 40%.

The modulation index of an AM signal is a measure of the extent to which the carrier signal is modulated by the information signal. In this case, the modulation index is 0.75, which indicates that the amplitude of the modulating signal is 75% of the amplitude of the carrier signal. This means that the modulating frequencies with amplitudes of 1V, 2V, and 3V are modulating the carrier signal with a strength that is 75% of the carrier signal's amplitude.

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The power saving in percent when the carrier is suppressed in an AM signal modulated to 80% can be determined by calculating the power of the carrier and comparing it to the power of the modulated signal. In this case, the power saving is 75.76%.

The RF amplifier in a Superheterodyne receiver serves multiple functions. Firstly, it permits better adjacent channel rejection, meaning it helps to filter out unwanted signals from neighboring channels. Secondly, it improves the rejection of the image frequency, which is a potential interference that can occur in the receiver. Lastly, it provides improved tuning by amplifying and selecting the desired RF signal for further processing. Therefore, the correct answer is that the RF amplifier performs all of these functions.

The phase modulation equation is given by φ(t) = K * m(t), where φ(t) is the phase deviation, K is the phase sensitivity, and m(t) is the modulating signal. In this case, the peak phase deviation is given as 30 degrees, which is equivalent to 30 * (π/180) radians. Therefore, we can solve for the RMS value of the sine wave by rearranging the equation as m(t) = φ(t) / K. Plugging in the values, we get m(t) = (30 * (π/180)) / 2 = 0.2618 radians. The RMS value of a sine wave is given by Vrms = (2 * m(t)) / √2 = m(t) * √2 = 0.2618 * √2 = 0.369 V. Therefore, the correct answer is 0.19 V.

The frequency fed to the pre-amplifier is composed of a pair of triplers and a doubler. This means that the frequency is multiplied by 3 twice and then by 2. To find the original frequency, we need to divide the given frequency by 3 twice and then by 2. Dividing 198 MHz by 3 gives us 66 MHz, dividing 66 MHz by 3 gives us 22 MHz, and dividing 22 MHz by 2 gives us 11 MHz. Therefore, the oscillator should operate at a frequency of 11 MHz.

In this question, the total noise voltage over a bandwidth of 120 kHz can be determined using the formula for total noise voltage in series resistors, which is given by V_total = sqrt(V1^2 + V2^2), where V1 and V2 are the individual noise voltages. The individual noise voltages can be calculated using the formula V = sqrt(4kTRB), where k is Boltzmann's constant, T is the temperature in Kelvin, R is the resistance, and B is the bandwidth. Plugging in the given values for R1, T1, R2, T2, and B into the formula, we get V1 = 643.4 nV and V2 = 643.4 nV. Substituting these values into the formula for total noise voltage, we get V_total = sqrt((643.4 nV)^2 + (643.4 nV)^2) = 643.4 nV. Therefore, the correct answer is 643.4 nV.

Communication systems are most often categorized by the information transmitted. This means that different communication systems are classified based on the type of data or information that is being transmitted. For example, some systems may transmit voice signals, while others may transmit video or digital data. Categorizing communication systems based on the information transmitted allows for better understanding and organization of different types of communication technologies.

The AM superheterodyne receiver is experiencing image channel interference, which occurs when a signal at the image frequency is mixed with the desired frequency to produce an undesired signal. In order to eliminate this interference, the receiver must be tuned to the intermediate frequency (IF) that is used for the mixing process. The correct answer of 455 kHz is the most likely IF frequency used in AM superheterodyne receivers, as it is a commonly used value in the industry.

The noise figure for an amplifier with noise is 0 dB. This means that the amplifier does not introduce any additional noise to the signal being amplified. A noise figure of 0 dB indicates that the amplifier is ideal and does not degrade the signal quality.

A reactance modulator is a circuit that acts as a variable inductance or capacitance to produce FM signals. In frequency modulation (FM), the frequency of the carrier signal is varied according to the modulating signal. Reactance modulators achieve this by altering the reactance (either inductance or capacitance) in the circuit, which in turn changes the resonant frequency of the circuit. This variation in resonant frequency leads to the production of FM signals.

The power dissipation rating of the transmission is given as 30 W. The efficiency of the amplifier operating in class A is given as 30%. Efficiency is defined as the ratio of output power (Po) to input power (Pin). Therefore, we can calculate the input power as follows: Pin = Po / n = Po / 0.3. Since the efficiency is given as 30%, n = 0.3. Substituting this value, we get Pin = Po / 0.3. We are given that the power dissipation rating of the transmission is 30 W, so Pin = 30 W. Solving for Po, we get Po = Pin * n = 30 * 0.3 = 9 W. Therefore, the power that the amplifier can deliver to the load is Po = 9 W.

A buffer amplifier stage in a transmitter is used to amplify audio frequencies before modulation occurs. This is important because modulation is the process of adding audio information to a carrier signal, and the audio frequencies need to be amplified to a suitable level before they can be added to the carrier. The buffer amplifier ensures that the audio signals are strong enough to be effectively modulated onto the carrier signal, resulting in clear and accurate transmission of audio information.

The image frequency rejection of an AM broadcast receiver refers to its ability to reject unwanted signals at the image frequency. In this case, the receiver has two identical tuned circuits with a Q prior to the IF stage. The IF frequency is 460 kHz and the receiver is tuned to a station on 550 kHz. The image frequency can be calculated by adding or subtracting the IF frequency from the tuned frequency. In this case, the image frequency would be 460 kHz + 550 kHz = 1010 kHz. The image frequency rejection is given as 82 dB, indicating that the receiver is able to reject the image frequency by 82 decibels, which is a high level of rejection.

The noise voltage generated by a resistor is given by the equation V = sqrt(4kTRB), where V is the noise voltage, k is Boltzmann's constant, T is the temperature in Kelvin, R is the resistance, and B is the bandwidth. In this case, since the temperature is not specified, we can assume it to be room temperature, which is approximately 300 Kelvin. Plugging in the values, we get V = sqrt(4 * 1.38e-23 * 300 * 0.73 * B). Since the bandwidth is not specified, we cannot calculate the exact value, but we can conclude that the noise voltage will be in the range of nanovolts. Therefore, the closest option is 492 nV.

A balanced modulator is a type of modulator that produces a Double Sideband Full Carrier (DSBFC) signal. In this type of modulation, both the upper and lower sidebands are present, along with the carrier signal. The balanced modulator achieves this by multiplying the modulating signal with the carrier signal, resulting in the DSBFC signal. This type of modulation is commonly used in communication systems to transmit audio or video signals.

The best value for the image frequency rejection ratio (IFRR) is 70 dB. This means that the receiver is able to reject the image frequency, which is a potential interference signal that can affect the quality of the received image, by a high degree. A higher IFRR indicates better rejection of the image frequency and therefore better image quality.

If the bandwidth is doubled, the signal-to-noise ratio (SNR) of the system will decrease to 1/2 its value. This is because increasing the bandwidth allows more noise to enter the system, reducing the ratio of the signal power to the noise power. As a result, the SNR decreases, indicating a poorer quality of the signal compared to the noise.