Question 1

The standard time constant used for pre-emphasis in a non-Dolby system is:

Accepted Answer

The standard time constant used for pre-emphasis in a non-Dolby system is 75 microseconds (us). This is commonly used in FM radio broadcasting to improve the signal-to-noise ratio.

Question 2

An FM signal has a center frequency of 154.5 MHz but is swinging between 154.45 MHz and 154.55 MHz at a rate of 500 times per second. Its index of modulation is:

Accepted Answer

The index of modulation (β) for an FM signal is calculated as the ratio of the frequency deviation (Δf) to the modulation frequency (fm). Here, Δf = 154.55 MHz - 154.45 MHz = 0.1 MHz = 100 kHz, and fm = 500 Hz. Thus, β = Δf / fm = 100,000 / 500 = 200. However, none of the provided options exactly match this calculation, suggesting a possible error in the interpretation of the question or in the provided options. Given the closest options, the correct response based on the standard formula would be to reevaluate the calculation or the understanding of the question. My initial response was based on a direct calculation error, assuming the closest provided option, but it's crucial to note the correct calculation method and acknowledge the discrepancy in the provided options.

Question 3

The first working FM system was developed by:

Accepted Answer

Armstrong is credited with developing the first working FM (Frequency Modulation) system. His contributions significantly advanced radio technology, making FM broadcasting possible.

Question 4

In an FM modulator, the intelligence frequency determines the:

Accepted Answer

The intelligence frequency in an FM modulator determines the rate of carrier frequency deviation, as it directly influences how fast the frequency of the carrier wave changes over time.

Question 5

An FM signal has a center frequency of 154.5 MHz, but is swinging between 154.45 MHz and 154.55 MHz at a rate of 500 times per second. Its input intelligence frequency is:

Accepted Answer

The input intelligence frequency is the rate at which the carrier frequency is modulated, which in this case is 500 times per second, or 500 Hz.

Question 6

An FM signal has an intelligence frequency of 5 kHz and a maximum deviation of 30 kHz. Its index of modulation is:

Accepted Answer

The index of modulation for an FM signal is calculated as the ratio of the maximum deviation to the intelligence frequency. Therefore, it is 30 kHz / 5 kHz = 6.

Question 7

The two types of angle modulation are:

Accepted Answer

The two types of angle modulation are phase modulation (PM) and frequency modulation (FM), both of which involve varying the phase or frequency of the carrier signal to encode information.

Question 8

Carson's rule is:

Accepted Answer

Carson's rule is used as a quick approximation method to find the bandwidth of an FM (Frequency Modulation) signal. It takes into account both the frequency deviation and the highest frequency in the modulating signal to estimate the bandwidth.

Question 9

Noise is usually clipped by:

Accepted Answer

Limiter circuits are specifically designed to clip or limit the amplitude of a signal, which can help in reducing noise that exceeds a certain threshold.

Question 10

In an FM modulator, the amplitude of the intelligence signal determines the:

Accepted Answer

The amplitude of the intelligence signal in an FM (Frequency Modulation) modulator determines the amount of carrier frequency deviation. This means that a higher amplitude in the intelligence signal will result in a greater deviation of the carrier frequency from its center frequency.

Question 11

An FM signal has a center frequency of 154.5 MHz but is swinging between 154.45 MHz and 154.55 MHz at a frequency of 500 times per second. Its input carrier frequency is:

Accepted Answer

The input carrier frequency is the center frequency around which the FM signal varies. In this case, it is 154.5 MHz.

Question 12

Standard FM broadcast stations use a maximum intelligence frequency of:

Accepted Answer

Standard FM broadcast stations use a maximum intelligence frequency of 15 kHz to ensure high-fidelity audio transmission within the allocated bandwidth.

Question 13

If the S/N of the input signal is 4 and the intelligence signal is 10 kHz, determine the deviation

Accepted Answer

The deviation can be calculated using Carson's rule, which states that the total bandwidth (BT) of an FM signal is approximately BT = 2(Δf + fm), where Δf is the frequency deviation and fm is the maximum modulating frequency. Given that the S/N (signal-to-noise ratio) for FM is proportional to (Δf/fm)^2, and assuming a linear relationship for simplicity, a S/N of 4 implies that Δf/fm = 2 (since 2^2 = 4). Given fm = 10 kHz, solving for Δf gives Δf = 2 * fm = 2 * 10 kHz = 20 kHz. However, without direct information on bandwidth or a clear method to apply the given S/N ratio directly to find deviation in the options provided, and considering typical FM calculations, the answer provided might not directly follow from the given explanation. The correct calculation should involve understanding that the deviation ratio is directly related to the quality of the signal and its bandwidth, but the specific values provided do not directly lead to a clear answer without additional context or assuming specific conditions that are not provided in the question. Therefore, the selection of "C" as the correct answer is incorrect based on the explanation provided, and there seems to be a misunderstanding in the application of the given information to solve for frequency deviation. The correct approach to determine the deviation would involve more specific information or formulas directly relating S/N ratio to deviation, which is not clearly provided in the question or the explanation.

Question 14

The amount of frequency deviation is proportional to the amplitude of the intelligence signal in:

Accepted Answer

The answer of The amount of frequency deviation is proportional...

Question 15

Which of the following is indirect FM generation?

Accepted Answer

Armstrong modulator is an indirect FM generation method that uses phase modulation to generate frequency modulation.

Question 16

Standard FM broadcast stations use a maximum frequency deviation of:

Accepted Answer

Standard FM broadcast stations in many countries, including the United States, use a maximum frequency deviation of 75 kHz. This is part of the FM broadcast standards to ensure a balance between signal quality and bandwidth efficiency.

Question 17

To solve for the frequency components of an FM signal, what high-level mathematical tool is used?

Accepted Answer

The answer of To solve for the frequency components of...

Question 18

The modulation index is:

Accepted Answer

The modulation index, especially in frequency modulation (FM) and phase modulation (PM), is defined as the ratio of the frequency deviation (how much the carrier frequency varies) to the modulating signal frequency (intelligence frequency). This is why option C is correct.

Question 19

Viewing an FM signal on a spectrum analyzer, if the carrier frequency component is zero and there are four or five sidebands on either side of the carrier frequency, the index of modulation is:

Accepted Answer

The index of modulation in frequency modulation (FM) can be estimated by observing the number of significant sidebands. The presence of four or five sidebands on either side of the carrier frequency suggests a moderate index of modulation, which is consistent with an index of around 2.2. This is because the number of significant sidebands in FM is approximately equal to the modulation index, which in this case, suggests an index of modulation around 2.2, fitting the description provided.

Question 20

Phase modulation is an indirect form of:

Accepted Answer

The answer of Phase modulation is an indirect form of:
...

Quiz 5: Frequency Modulation: Transmission