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Questions and Answers
What is the ratio of total side band power to the total power in the modulated wave called?
What type of device is a square law modulator?
What is the frequency of the dc component in the output of a square law modulator?
What is the purpose of a band pass filter in a switching modulator?
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What is the output of a switching modulator when c(t) is positive?
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What is the process of recovering the original information signal from the modulated wave called?
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What is the expression for the total input to a square law device in an AM wave?
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What is the frequency range of the information signal in an AM wave?
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What is the frequency range for AM in radio broadcasting?
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What is the bandwidth of an AM wave?
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What is the equation for an amplitude modulated signal?
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What is the significance of 'ka' in amplitude modulation?
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What is the condition for the carrier frequency in amplitude modulation?
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What is the name of the modulation scheme where the amplitude of the carrier is varied linearly by the modulating signal?
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What is the modulation index in amplitude modulation?
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What is the Fourier Transform of the amplitude modulated signal?
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Study Notes
Amplitude Modulation (AM)
- Amplitude Modulation is the process of changing the amplitude of a high-frequency carrier signal in accordance with the amplitude of the modulating signal (information).
- The carrier amplitude is varied linearly by the modulating signal, which usually consists of a range of audio frequencies.
- The frequency of the carrier is not affected.
Applications of AM
- Radio broadcasting
- TV pictures (video)
- Facsimile transmission
Frequency Range and Bandwidth of AM
- Frequency range: 535 kHz – 1600 kHz
- Bandwidth: 10 kHz
Forms of Amplitude Modulation
- Conventional Amplitude Modulation (Full AM or Double Sideband Large carrier modulation (DSBLC) / Double Sideband Full Carrier (DSBFC))
- Double Sideband Suppressed carrier (DSBSC) modulation
- Single Sideband (SSB) modulation
- Vestigial Sideband (VSB) modulation
Time and Frequency Domain Description
- Amplitude modulated signal: s(t) = Ac [1 + kam(t)] cos(ωct)
- Fourier Transform: S(ω) = π Ac/2 (δ(ω − ωc) + δ(ω + ωc)) + kaAc/ 2 (M(ω − ωc) + M(ω + ωc))
Single Tone Modulation
- Modulating wave: m(t) = Acm cos(ωmt)
- Amplitude modulated signal: s(t) = Ac [1 + kam cos(ωmt)] cos(ωct)
Power Relations in AM Waves
- Ratio of total sideband power to total power in the modulated wave is called the efficiency of the AM system
Generation of AM Waves
- Two basic amplitude modulation principles:
- Square law modulation
- Switching modulator
Square Law Modulator
- Output of a non-linear device is not directly proportional to the input throughout the operation
- Input-Output relation: y(t) = a1x(t) + a2x^2(t)
- Square law device output: V0 = Vdc + Vm cos(ωmt)
Switching Modulator
- Total input for the diode: v1 = Ac cos(ωct) + m(t)
- When c(t) is positive, v2=v1, and when c(t) is negative, v2=0
- Switching response of the diode: v2 = v1 * s(t)
Detection of AM Waves
- Demodulation is the process of recovering the original message signal from the amplitude-modulated wave.
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Description
Learn about amplitude modulation systems, including the generation and detection of AM waves. Understand the process of amplitude modulation and its applications.