先决条件 – 调制
1. 调幅：
幅度调制是一种调制，其中载波的幅度根据调制信号的瞬时幅度而变化，保持相位和频率不变。修改载波的幅度以发送数据或信息。它可以远距离传输，具有很大的范围。它的调制指数从 0 到 1 不等。在 Amplitude Modulation 中，频率和相位保持不变。
2. 相位调制：
相位调制是一种调制，其中载波的相位根据调制信号的瞬时幅度变化，保持幅度和频率不变。 Phase Modulation 和Frequency Modulation 类似，但在Phase Modulation 中，载波信号的频率没有增加。相位调制用于移动系统。修改载波的相位以发送数据或信息。
调幅和调相的区别：
| S.NO. | Amplitude Modulation | Phase Modulation |
|---|---|---|
| 1. | In Amplitude Modulation, the frequency remains the same. | In Phase Modulation, the amplitude remains the same. |
| 2. | It has simple circuit. | It has complex circuit. |
| 3. | Its modulation index varies from 0 to 1. | Its modulation index is always greater than one. |
| 4. | Noise immunity is poor than in PM. | Noise immunity is better than in AM. |
| 5. | In Amplitude Modulation, the phase remains the same. | In Phase Modulation, the frequency remains the same. |
| 6. | Amplitude Modulation is widely used. | Phase Modulation is used in mobile system. |
| 7. | Signal to noise ratio is better than Phase Modulation. | Signal to noise ratio is poor than Amplitude Modulation. |
| 8. | The amplitude of the carrier wave is modified in order to send the data or information. | The phase of the carrier wave is modified in order to send the data or information. |
| 9. | In AM, received signal is of low quality. | In FM, received signal is of high quality. |
| 10. | It has better sound quality. | It has poor sound quality. |