Amplitude Modulation (AM) in Continuous Wave (CW)

• Continuous Wave (CW) Modulation: a technique where a high-frequency carrier signal's amplitude, frequency, or phase is varied in accordance with the message signal

Amplitude Modulation (AM)

• Amplitude Modulation (AM): the amplitude of the carrier signal is varied in proportion to the instantaneous amplitude of the message signal
• The frequency of the carrier signal remains constant in AM
• AM signal equation: s(t) = Ac[1 + kam(t)]cos(2πfct), where Ac is the carrier amplitude, ka is the modulation index, m(t) is the message signal, and fc is the carrier frequency
• Modulation Index (ka): a measure of the extent of amplitude variation around an unmodulated carrier level
• For distortion-free AM transmission, ka should be less than or equal to 1
• Overmodulation (where ka > 1) leads to signal distortion
• AM signal consists of the carrier frequency (fc) and two sidebands: upper sideband (fc + fm) and lower sideband (fc - fm), where fm is the message frequency
• Bandwidth of AM signal: twice the highest frequency component of the message signal (2fm)
• AM is simple to implement, but it's susceptible to noise and interference
• AM is used in radio broadcasting, aviation communication, and older communication systems

Frequency Modulation (FM)

• Frequency Modulation (FM): the frequency of the carrier signal is varied in proportion to the instantaneous amplitude of the message signal
• The amplitude of the carrier signal remains constant in FM
• FM signal equation: s(t) = Ac cos[2πfct + βsin(2πfmt)], where Ac is the carrier amplitude, fc is the carrier frequency, fm is the message frequency, and β is the modulation index
• Modulation Index (β): Defined as the ratio of the maximum frequency deviation to the message signal frequency, β = Δf/fm
• Frequency Deviation (Δf): the maximum change in the carrier frequency from its unmodulated value
• Bandwidth of FM Signal: approximated by Carson's rule: BW = 2(Δf + fm), where Δf is the peak frequency deviation and fm is the highest frequency in the modulating signal
• FM offers better noise immunity compared to AM
• FM requires a wider bandwidth than AM
• FM is used in FM radio broadcasting, television sound broadcasting, and some mobile communication systems

Phase Modulation (PM)

• Phase Modulation (PM): the phase of the carrier signal is varied in proportion to the instantaneous amplitude of the message signal
• The amplitude and frequency of the carrier signal remain constant in PM
• PM signal equation: s(t) = Ac cos[2πfct + kpm(t)], where Ac is the carrier amplitude, fc is the carrier frequency, m(t) is the message signal, and kp is the phase deviation constant
• Phase Deviation (Δφ): the maximum change in the phase of the carrier signal
• Bandwidth of PM Signal: similar to FM, approximated by Carson's rule, depends on the maximum phase deviation and the message signal frequency
• PM is mathematically related to FM (frequency is the derivative of phase)
• PM also provides good noise immunity
• PM is used in satellite communication, mobile communication, and data transmission systems

Key Differences and Trade-offs

• Bandwidth: AM has the narrowest bandwidth, followed by FM and PM (FM and PM bandwidth depends on modulation index and message signal characteristics)
• Noise Immunity: FM and PM offer better noise immunity than AM
• Complexity: AM is the simplest to implement, followed by FM, while PM can be more complex
• Applications: AM is suitable where simplicity and narrow bandwidth are important. FM and PM are preferred where noise immunity is critical

Modulation Index

• The modulation index in AM determines the efficiency of power transmission
• In FM and PM, modulation index affects the bandwidth and signal-to-noise ratio
• Higher modulation index in FM and PM leads to wider bandwidth but potentially better noise performance (up to a certain point)

Power Efficiency

• In AM, a significant portion of the transmitted power is in the carrier, which carries no information
• In FM and PM, the power is distributed among the carrier and sidebands, and the carrier power can be suppressed in some implementations, leading to better power efficiency

Explanation of Amplitude Modulation (AM), a type of Continuous Wave (CW) modulation where the carrier signal's amplitude changes with the message signal. It covers the AM signal equation, modulation index, and the importance of keeping the modulation index under 1 to prevent distortion. Includes discussion of sidebands.