Analog Communication: Amplitude Modulation Systems

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?

What is the output of a switching modulator when c(t) is positive?

What is the process of recovering the original information signal from the modulated wave called?

What is the expression for the total input to a square law device in an AM wave?

What is the frequency range of the information signal in an AM wave?

What is the frequency range for AM in radio broadcasting?

What is the bandwidth of an AM wave?

What is the equation for an amplitude modulated signal?

What is the significance of 'ka' in amplitude modulation?

What is the condition for the carrier frequency in amplitude modulation?

What is the name of the modulation scheme where the amplitude of the carrier is varied linearly by the modulating signal?

What is the modulation index in amplitude modulation?

What is the Fourier Transform of the amplitude modulated signal?

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.

Learn about amplitude modulation systems, including the generation and detection of AM waves. Understand the process of amplitude modulation and its applications.