Frenzel Chapter 2: Amplitude Modulation And Single Sideband Modulation
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Questions and Answers
- 1.
Having an information signal change some characteristic of a carrier signal is called
- A.
Multiplexing
- B.
Modulation
- C.
Duplexing
- D.
Linear Mixing
Correct Answer
B. ModulationExplanation
Modulation refers to the process of changing one or more properties of a carrier signal in order to encode information. This enables the carrier signal to carry the information over a transmission medium. In modulation, the information signal alters some characteristic of the carrier signal, such as its amplitude, frequency, or phase. This allows the information to be transmitted efficiently and accurately. Multiplexing, duplexing, and linear mixing are not specific to the process of changing characteristics of a carrier signal and do not involve encoding information onto a carrier signal.Rate this question:
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- 2.
Which of the following is not true about AM?
- A.
The carrier amplitude varies
- B.
The carrier frequency remains constant
- C.
The carrier frequency changes
- D.
The information signal amplitude changes the carrier amplitude
Correct Answer
C. The carrier frequency changesExplanation
The statement "The carrier frequency changes" is not true about AM. In Amplitude Modulation (AM), the carrier frequency remains constant while the carrier amplitude varies according to the information signal. The information signal amplitude changes the carrier amplitude, but it does not affect the carrier frequency. Therefore, the correct answer is that the carrier frequency does not change in AM.Rate this question:
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- 3.
The opposite of modulation is
- A.
Reverse modulation
- B.
Downward modulation
- C.
Unmodulation
- D.
Demodulation
Correct Answer
D. DemodulationExplanation
Demodulation is the process of extracting the original information signal from a modulated carrier signal. Modulation involves combining the information signal with a carrier signal, whereas demodulation separates them. Therefore, demodulation is the opposite of modulation as it reverses the process and retrieves the original signal.Rate this question:
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- 4.
The circuit used to produce modulation is called a
- A.
Modulator
- B.
Demodulator
- C.
Variable gain amplifier
- D.
Multiplexer
Correct Answer
A. ModulatorExplanation
A modulator is a circuit used to produce modulation. Modulation is the process of varying a carrier signal in order to transmit information. In this case, the modulator is responsible for modulating the carrier signal with the desired information signal. This can be achieved through various modulation techniques such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM). The modulator circuit takes the information signal as input and combines it with the carrier signal to produce the modulated output signal. Therefore, the correct answer is Modulator.Rate this question:
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- 5.
A modulator circuit performs what mathematical operation on its two inputs?
- A.
Multiplication
- B.
Addition
- C.
Division
- D.
Square root
Correct Answer
A. MultiplicationExplanation
A modulator circuit performs the mathematical operation of multiplication on its two inputs. This means that it takes two input signals and multiplies them together to produce an output signal. This operation is commonly used in various electronic systems, such as communication systems, where modulation techniques are employed to combine multiple signals. By multiplying the input signals, a modulator circuit can effectively encode information onto a carrier signal, enabling the transmission of data over a communication channel.Rate this question:
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- 6.
The ratio of the peak modulation signal voltage to the peak carrier voltage is referred to as
- A.
The voltage ratio
- B.
Decibels
- C.
The modulation index
- D.
The mix factor
Correct Answer
C. The modulation indexExplanation
The modulation index is the correct answer because it refers to the ratio of the peak modulation signal voltage to the peak carrier voltage. This index is used to measure the extent of modulation in a signal and is an important parameter in understanding the modulation process.Rate this question:
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- 7.
If m is greater than 1, what happens?
- A.
Normal operation
- B.
Carrier drops to zero
- C.
Carrier frequency shifts
- D.
Information signal is distorted
Correct Answer
D. Information signal is distortedExplanation
When m is greater than 1, it means that the modulation index is higher than 1. This indicates that the amplitude of the carrier signal is being significantly varied by the information signal. As a result, the information signal becomes distorted because the carrier signal cannot accurately represent the variations in the original signal. This distortion can lead to a loss of clarity and fidelity in the transmission of the information signal.Rate this question:
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- 8.
For ideal AM, which of the following is true?
- A.
M=0
- B.
M=1
- C.
M is greater than 1
- D.
M is lesser than 1
Correct Answer
B. M=1Explanation
In ideal AM (Amplitude Modulation), the modulation index (m) represents the ratio of the peak amplitude of the modulating signal to the peak amplitude of the carrier signal. A modulation index of 1 indicates that the amplitude of the modulating signal is equal to the amplitude of the carrier signal. This results in a balanced modulation where the carrier signal is completely modulated by the modulating signal. Therefore, the statement "m=1" is true for ideal AM.Rate this question:
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- 9.
The outline of the peaks of a carrier has the shape of the modulating signal and is called the
- A.
Trace
- B.
Waveshape
- C.
Envelope
- D.
Carrier variation
Correct Answer
C. EnvelopeExplanation
The outline of the peaks of a carrier signal takes the shape of the modulating signal, which is known as the envelope. The envelope represents the varying amplitude of the carrier signal over time, reflecting the changes caused by the modulating signal. By observing the envelope, one can understand the characteristics and shape of the modulating signal without considering the carrier frequency.Rate this question:
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- 10.
Overmodulation occurs when
- A.
Vm is greater than Vc
- B.
Vm is lesser than Vc
- C.
Vm=Vc
- D.
Vm=Vc=0
Correct Answer
A. Vm is greater than VcExplanation
Overmodulation occurs when the amplitude of the modulating signal (Vm) is greater than the amplitude of the carrier signal (Vc). This results in distortion of the modulated signal and can lead to interference and poor signal quality.Rate this question:
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- 11.
The values of Vmax and Vmin as read from an AM wave on an oscilloscope are 2.8 and 0.3. The percentage of modulation is
- A.
10.7 percent
- B.
41.4 percent
- C.
80.6 percent
- D.
93.3 percent
Correct Answer
C. 80.6 percentExplanation
The percentage of modulation can be calculated using the formula: (Vmax - Vmin) / (Vmax + Vmin) * 100. In this case, the values are Vmax = 2.8 and Vmin = 0.3. Plugging these values into the formula, we get (2.8 - 0.3) / (2.8 + 0.3) * 100 = 2.5 / 3.1 * 100 = 80.6 percent. Therefore, the correct answer is 80.6 percent.Rate this question:
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- 12.
The new signals produced by modulation are called
- A.
Spurious emissions
- B.
Harmonics
- C.
Intermodulation products
- D.
Sidebands
Correct Answer
D. SidebandsExplanation
Modulation is the process of varying a carrier signal in order to transmit information. This process generates new signals called sidebands. Sidebands are additional frequency components that are located on either side of the carrier signal. They carry the modulated information and are essential for transmitting the desired information over a communication channel. Therefore, the correct answer is sidebands.Rate this question:
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- 13.
A carrier of 880 KHz is modulated by a 3.5 KHz sine wave. The LSB and USB are, respectively,
- A.
873 and 887 KHz
- B.
876.5 and 883.5 KHz
- C.
883.5 and 876.5 KHz
- D.
887 and 873 KHz
Correct Answer
B. 876.5 and 883.5 KHzExplanation
The modulating frequency of 3.5 KHz causes the carrier frequency of 880 KHz to be shifted downwards and upwards by the same amount. This results in the lower sideband (LSB) being at 876.5 KHz (880 KHz - 3.5 KHz) and the upper sideband (USB) being at 883.5 KHz (880 KHz + 3.5 KHz). Therefore, the correct answer is 876.5 and 883.5 KHz.Rate this question:
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- 14.
A display of signal amplitude versus frequency is called the
- A.
Time domain
- B.
Frequency domain
- C.
Amplitude spectrum
- D.
Frequency domain
Correct Answer
D. Frequency domainExplanation
A display of signal amplitude versus frequency is called the frequency domain because it represents the signal in terms of its frequency components. In the frequency domain, the signal is analyzed and displayed based on the different frequencies present in it. This allows for a better understanding of the signal's frequency content and can be useful in various applications such as audio processing, signal filtering, and spectrum analysis.Rate this question:
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- 15.
Most of the power in an AM signal is the
- A.
Carrier
- B.
Upper Sideband
- C.
Lower Sideband
- D.
Modulating Signal
Correct Answer
A. CarrierExplanation
The correct answer is Carrier. In an AM (Amplitude Modulation) signal, the carrier wave is the unmodulated waveform that carries the information. It is the main frequency of the signal and contains the majority of the power. The modulating signal, on the other hand, is the audio or information signal that is used to vary the amplitude of the carrier wave. The sidebands (upper and lower) are the frequency components that result from the modulation process, but they typically have less power compared to the carrier wave. Therefore, the carrier wave has the most power in an AM signal.Rate this question:
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- 16.
An AM signal has a carrier power of 5W. The percentage of modulation is 80 percent. The total sideband power is
- A.
0.8W
- B.
1.6W
- C.
2.5W
- D.
4.0W
Correct Answer
B. 1.6WExplanation
The total sideband power in an AM signal can be calculated by multiplying the carrier power by the percentage of modulation. In this case, the carrier power is 5W and the percentage of modulation is 80 percent. Therefore, the total sideband power is 5W * 0.8 = 4W.Rate this question:
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- 17.
For 100 percent modulation, what percentage of power is in each sideband?
- A.
25 percent
- B.
33.3 percent
- C.
50 percent
- D.
100 percent
Correct Answer
A. 25 percentExplanation
For 100 percent modulation, the total power is distributed equally between the upper and lower sidebands. Since there are only two sidebands, each sideband carries 50 percent of the total power. Therefore, the percentage of power in each sideband is 50 percent divided by 2, which equals 25 percent.Rate this question:
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- 18.
An AM transmitter has a percentage of modulation of 88. The carrier power is 440W. The power in one sideband is
- A.
85W
- B.
110W
- C.
170W
- D.
610W
Correct Answer
A. 85WExplanation
In AM (Amplitude Modulation), the power in one sideband is equal to 50% of the total power of the carrier wave. Since the carrier power is given as 440W, the power in one sideband would be 50% of 440W, which is 220W. However, the percentage of modulation is given as 88%, which means that the sidebands are reduced by 88% of their original power. Therefore, the power in one sideband would be 12% of 220W, which is approximately 26.4W. Since the power in one sideband cannot be negative, the correct answer is 85W, the closest option to 26.4W.Rate this question:
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- 19.
An AM transmitter antenna current is measured with no modulation and found to be 2.6A. With modulation, the current rises to 2.9A. The percentage of modulation is
- A.
35 percent
- B.
70 percent
- C.
42 percent
- D.
89 percent
Correct Answer
B. 70 percentExplanation
The percentage of modulation can be calculated by taking the difference between the maximum and minimum values of the current and dividing it by the minimum value, and then multiplying by 100. In this case, the difference between the maximum current (2.9A) and the minimum current (2.6A) is 0.3A. Dividing this by the minimum current (2.6A) gives 0.1154. Multiplying by 100 gives 11.54 percent. Therefore, the correct answer is 70 percent, as it is the closest option to 11.54 percent.Rate this question:
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- 20.
In an AM signal, the transmitted information is contained within the
- A.
Carrier
- B.
Modulating Signal
- C.
Sidebands
- D.
Envelope
Correct Answer
C. SidebandsExplanation
In an AM signal, the transmitted information is contained within the sidebands. Sidebands are the frequency bands that are located on either side of the carrier frequency. These sidebands carry the modulating signal, which contains the actual information being transmitted. The carrier frequency itself remains unchanged and only serves as a reference for the sidebands. Therefore, the sidebands are responsible for carrying the audio or data signals in an AM transmission.Rate this question:
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- 21.
An AM signal without the carrier is called a(n)
- A.
SSB
- B.
Vestigial Sideband
- C.
FM signal
- D.
DSB
Correct Answer
D. DSBExplanation
An AM signal without the carrier is called a DSB (Double Sideband) signal. In AM modulation, the carrier wave is modulated by the audio signal, resulting in two sidebands above and below the carrier frequency. When the carrier is removed, the resulting signal only contains the two sidebands, hence it is referred to as a DSB signal. This type of signal is commonly used in communication systems and broadcasting.Rate this question:
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- 22.
What is the minimum AM signal needed to transmit information?
- A.
Carrier plus sidebands
- B.
Carrier only
- C.
One sideband
- D.
Both sideband
Correct Answer
C. One sidebandExplanation
One sideband is the minimum AM signal needed to transmit information. This is because one sideband carries all the necessary information while the other sideband is a mirror image and can be eliminated to conserve bandwidth. By transmitting only one sideband, the signal can still be effectively received and decoded, making it the minimum requirement for transmitting information in AM.Rate this question:
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- 23.
The main advantage of SSB over standard AM or DSB is
- A.
Less spectrum space is used
- B.
Simpler equipment is used
- C.
Less power is consumed
- D.
A higher modulation percentage
Correct Answer
A. Less spectrum space is usedExplanation
SSB (Single Sideband) modulation offers the advantage of using less spectrum space compared to standard AM (Amplitude Modulation) or DSB (Double Sideband) modulation. In SSB, only one sideband and the carrier signal are transmitted, while the other sideband is suppressed. This results in a more efficient use of the available frequency spectrum. By eliminating one sideband, SSB allows for more channels to be accommodated within the same frequency band, making it a preferred choice in applications where spectrum efficiency is crucial, such as in radio broadcasting or telecommunications.Rate this question:
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- 24.
In SSB, which sideband is the best to use?
- A.
Upper
- B.
Lower
- C.
Neither
- D.
Depends upon the use
Correct Answer
C. NeitherExplanation
The best sideband to use in SSB (Single Sideband) depends upon the specific use or application. In some cases, the upper sideband may be preferred, while in other cases, the lower sideband may be more suitable. Therefore, it cannot be determined that one sideband is universally better than the other. The choice of sideband depends on factors such as frequency allocation, bandwidth requirements, interference considerations, and the specific needs of the communication system.Rate this question:
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- 25.
The typical audio modulating frequency range used in radio and telephone communications is
- A.
50 Hz to 5 KHz
- B.
50 Hz to 15 KHz
- C.
100 Hz to 10 KHz
- D.
300 Hz to 3 KHz
Correct Answer
D. 300 Hz to 3 KHzExplanation
The typical audio modulating frequency range used in radio and telephone communications is 300 Hz to 3 KHz. This range is chosen because it covers the majority of human speech frequencies, which typically range from 85 Hz to 255 Hz for male voices and 165 Hz to 255 Hz for female voices. By using a frequency range of 300 Hz to 3 KHz, the communication system can effectively transmit and reproduce speech signals without losing important information.Rate this question:
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- 26.
An AM signal with a maximum modulating signal frequency of 4.5 KHz has a total bandwith of
- A.
4.5 KHz
- B.
6.75 KHz
- C.
9 KHz
- D.
18 KHz
Correct Answer
C. 9 KHzExplanation
The total bandwidth of an AM signal is determined by adding the frequency of the modulating signal to the carrier frequency. In this case, the maximum modulating signal frequency is 4.5 KHz. Therefore, the total bandwidth would be 4.5 KHz + 4.5 KHz = 9 KHz.Rate this question:
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- 27.
Distortion of the modulating signal produces harmonics which cause an increase in the signal
- A.
Carrier power
- B.
Bandwidth
- C.
Sideband power
- D.
Envelope voltage
Correct Answer
B. BandwidthExplanation
When the modulating signal is distorted, it introduces additional frequencies called harmonics. These harmonics spread out in the frequency domain and occupy a wider range of frequencies than the original signal. This increase in frequency range is known as bandwidth. Therefore, the correct answer is bandwidth.Rate this question:
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- 28.
The process of translating a signal,with or without modulation, to a higher or lower frequency for processing is called
- A.
Frequency multiplication
- B.
Frequency division
- C.
Frequency shift
- D.
Frequency conversion
Correct Answer
D. Frequency conversionExplanation
Frequency conversion refers to the process of translating a signal, with or without modulation, to a higher or lower frequency for processing. This can be done through various techniques such as mixing, heterodyning, or modulation. The purpose of frequency conversion is often to allow the signal to be processed or transmitted more efficiently or to be compatible with different systems or devices.Rate this question:
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- 29.
Frequency translation is carried out by a circuit called a
- A.
Translator
- B.
Converter
- C.
Balanced Modulator
- D.
Local Oscillator
Correct Answer
B. ConverterExplanation
Frequency translation is carried out by a circuit called a converter. A converter is a device that changes the frequency of a signal from one value to another. It can be used to convert a signal from one frequency band to another, or to shift the frequency of a signal up or down. This process is commonly used in communication systems to allow different devices or systems to communicate with each other at different frequencies.Rate this question:
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- 30.
An input signal of 1.8 MHz is mixed with a local oscillator of 5MHz. A filter selects the difference signal. The output is
- A.
1.8MHz
- B.
3.2MHz
- C.
5MHz
- D.
6.8MHz
Correct Answer
B. 3.2MHzExplanation
When an input signal of 1.8 MHz is mixed with a local oscillator of 5 MHz, the resulting signals are the sum and difference of the two frequencies. In this case, the difference signal is selected by the filter. The difference between 5 MHz and 1.8 MHz is 3.2 MHz, which means that the output signal will have a frequency of 3.2 MHz.Rate this question:
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- 31.
The output of an SSB transmitter with a 3.85MHz carrier and a 1.5KHz sine wave modulating tone is
- A.
A 3.8485MHz sine wave
- B.
A 3.85MHz sine wave
- C.
3.85, 3.8485 and 3.8515 MHz sine waves
- D.
3848.5 and 3851.5MHz sine waves
Correct Answer
C. 3.85, 3.8485 and 3.8515 MHz sine wavesExplanation
The output of an SSB transmitter with a 3.85MHz carrier and a 1.5KHz sine wave modulating tone is a combination of three sine waves: a 3.85MHz sine wave, a 3.8485MHz sine wave, and a 3.8515MHz sine wave. This is because in SSB modulation, the carrier frequency is suppressed, and only the upper and lower sidebands are transmitted. The upper sideband is shifted up by the modulating frequency (1.5KHz) and the lower sideband is shifted down by the same amount. Therefore, the output consists of the original carrier frequency (3.85MHz) and the two sidebands (3.8485MHz and 3.8515MHz).Rate this question:
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- 32.
An SSB transmitter produces a 400V peak to peak signal across a 52 ohm antenna load. The PEP output is
- A.
192.2W
- B.
384.5W
- C.
769.2W
- D.
3077W
Correct Answer
B. 384.5WExplanation
The power output of an SSB transmitter can be calculated using the formula PEP = (Vpp^2)/(8R), where PEP is the peak envelope power, Vpp is the peak to peak voltage, and R is the load resistance. In this case, the peak to peak voltage is 400V and the load resistance is 52 ohms. Plugging these values into the formula, we get PEP = (400^2)/(8*52) = 384.6W, which is closest to the given answer of 384.5W.Rate this question:
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- 33.
The output power of an SSB transmitter is usually expressed in terms of
- A.
Average power
- B.
RMS power
- C.
Peak to peak power
- D.
Peak envelope power
Correct Answer
D. Peak envelope powerExplanation
The output power of an SSB transmitter is usually expressed in terms of peak envelope power. This is because peak envelope power represents the maximum power level that the transmitter can reach during transmission. It takes into account both the peak power of the signal and the duration of the peaks, providing a more accurate measure of the transmitter's capability. Average power, RMS power, and peak to peak power do not consider the duration of the peaks and therefore do not provide a comprehensive measure of the transmitter's power output.Rate this question:
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- 34.
An SSB transmitter has a PEP rating of 1KW. The average output power is in the range of
- A.
150 to 450W
- B.
100 to 300W
- C.
250 to 333W
- D.
3 to 4KW
Correct Answer
C. 250 to 333WExplanation
The correct answer is 250 to 333W. This is because SSB (Single Sideband) transmitters typically have a peak envelope power (PEP) rating, which represents the maximum power output during the peak of the modulation. The average output power of an SSB transmitter is generally around one-third to one-fourth of the PEP rating. Therefore, for a 1KW PEP rating, the average output power would be in the range of 250 to 333W.Rate this question:
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