2D AM FM PM comparision

Comparison of AM, FM, PM

1. Definition

• Amplitude Modulation (AM): A technique of modulation in which the amplitude of the carrier wave varies in accordance with the amplitude of the modulating signal. The frequency and phase of the carrier remain constant. This technique is commonly used in commercial radio broadcasting due to its simplicity and coverage ability.

• Frequency Modulation (FM): A technique in which the frequency of the carrier varies in accordance with the amplitude of the modulating signal. The amplitude and phase remain constant. This method is preferred for its fidelity and resistance to noise, particularly in music transmission.

• Phase Modulation (PM): A method in which the phase of the carrier wave is varied according to the amplitude of the modulating signal. Similar to FM, the amplitude and frequency stay constant. PM is often utilized in digital communication systems, especially in the context of phase-shift keying (PSK).

2. Variable Parameter

• AM: Modulation is based on changes in amplitude.

• FM: Modulation varies frequency depending on the signal amplitude.

• PM: Phase of the carrier is what changes.

3. Information Carried Through

• AM: The modulating signal is represented through variations in amplitude of the carrier wave (Ec + Em), which can lead to susceptibility to noise.

• FM: The modulation signal is carried over changes in frequency, providing higher fidelity.

• PM: Information is carried through changes in the phase of the carrier wave, similar to FM but with distinct properties in signal processing.

4. Waveforms

• AM: Depicted as variations in amplitude over time against a constant frequency carrier wave.

• FM: Illustrated as variations in frequency with respect to the invariant amplitude.

• PM: Represented by shifts in the phase angle in sine wave patterns, showing the behavior of the signal under modulation.

5. Bandwidth

• AM: The bandwidth requirement is typically expressed as 2fm (twice the highest modulating frequency).

• FM: Bandwidth is represented using Carson's rule: 2(Smax + fm(max)), where Smax is the maximum deviation from the carrier frequency and fm(max) is the maximum frequency of the modulating signal.

• PM: The formula for bandwidth is represented as 2(8 + fm), indicating increased bandwidth compared to AM.

6. Noise Immunity

• AM: Exhibits very poor noise immunity due to its reliance on amplitude variations, which can be easily affected by external disturbances.

• FM: Offers excellent noise immunity, as variations in frequency are less susceptible to amplitude interference.

• PM: Shows moderate noise immunity, benefiting from phase invariance compared to amplitude-modulated signals.

7. Design Complexity

• AM: Involves a simple design process, making it accessible for implementation in various technologies.

• FM: The design is complex because of its frequency deviation requirements and dependency on modulating signal dynamics.

• PM: Also features a complex design akin to FM, requiring precise control and adjustments.

8. Efficiency

• AM: Typically demonstrates lower efficiency and power use, which can waste energy in signal transmission.

• FM: Known for its better efficiency, it makes fuller use of the available power.

• PM: Comparatively displays better efficiency, largely depending on the modulation type applied.

9. Signal to Noise Ratio

• AM: Displays a poor signal-to-noise ratio, which contributes to lower quality audio performance in practice.

• FM: Achieves excellent signal-to-noise ratio, resulting in higher audio clarity and radio transmission quality.

• PM: Maintains a moderate signal-to-noise ratio, providing a balance between performance and fidelity.

10. Number of Sidebands

• AM: Can create an infinite number of sidebands, expanding its frequency spectrum considerably.

• FM: Generally does not specify the number of sidebands in conventional terms.

• PM: Similar to FM, its sideband composition varies with the modulation signal’s characteristics.

11. Mode of Propagation

• AM: Uses space wave propagation for longer ranges, making it suitable for wide-area broadcasting.

• FM: Employs both ground wave and sky wave propagation, benefiting urban and rural transmission.

• PM: Typically aligned with FM propagation methods, depending on application specifics.

12. Applications

• AM: Predominantly found in amplitude-modulated radio broadcasting, especially for news and talk radio.

• FM: Widely used in both radio and TV transmissions, noted for higher audio quality, making it favorable for music broadcasts.

• PM: Digital forms of phase modulation are widely used in data communication, including in cellular networks and Wi-Fi transmissions.

Representation of FM

FM in Frequency Domain:The frequency domain representation of FM is often referred to as the spectrum, depicting the continuous variation of voltage with respect to frequency. This spectrum illustrates how frequency changes correlate with specific modulation voltages.

FM in Time Domain:The time domain representation of FM is a plot of amplitude versus time, showing how the amplitude changes relate to time as the frequency varies. This is illustrated with respect to the frequency spectrum, where sidebands (Lower Sidebands (LSBs) and Upper Sidebands (USBs)) represent frequency deviations (E, c, o, fc-3fm, fc, fc+3fm, etc.).

This comprehensive overview compares different modulation techniques of AM, FM, and PM, focusing on their characteristics, design complexities, applications, and graphical representations.