先决条件 – 调制
1. 频率调制:
频率调制是一种调制,其中载波的频率根据调制信号的瞬时幅度而变化,保持相位和幅度不变。修改载波的频率以发送数据或信息。它不能长距离传输,范围更小。它的调制指数总是大于一。在频率调制中,幅度和相位保持不变。
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,保持幅度和频率恒定。 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。调频和调相的区别:
S.NO. | Frequency Modulation | Phase Modulation |
---|---|---|
1. | In Frequency Modulation amplitude and phase remain the same. | In Phase Modulation, the frequency and amplitude remain the same. |
2. | Frequency Modulation is proportional to modulating voltage. | Phase Modulation is proportional to modulating voltage. |
3. | Associated with the change in frequency, there is some phase change. | Associated with the change in phase, there is some frequency change. |
4. | It is possible to receive FM on a PM receiver. | It is possible to receive PM on a FM receiver. |
5. | Noise immunity is poor than AM and PM. | Noise immunity is better than AM but worst than PM. |
6. | Signal to noise ratio is better than in phase modulation. | Signal to noise ratio is poor than in frequency modulation. |
7. | Frequency Modulation is widely used. | Phase Modulation is used in mobile system. |
8. | In FM, the frequency derivation is proportional to the modulating voltage only. | In PM, the frequency derivation is proportional to the modulating voltage as well as modulating frequency. |
9. | Amplitude of FM wave is constant. | Amplitude of PM wave is also constant. |
10. | In FM, received signal is of high quality. | In PM, received signal is of low quality. |