vaihemodulaatiojärjestelmissä

vaihemodulaatio is a type of angle modulation where the phase of a carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal. This is in contrast to frequency modulation (FM), where the frequency of the carrier signal is varied, and amplitude modulation (AM), where the amplitude of the carrier signal is varied.

In phase modulation, the carrier signal can be represented as Ac cos(ωc t + φc), where Ac is the amplitude, ωc is the angular frequency, and φc is the initial phase. The modulating signal is represented as m(t). The phase-modulated signal, v(t), is given by Ac cos(ωc t + β m(t)), where β is the modulation index. The modulation index determines the extent of phase variation. A larger β results in a wider phase deviation for a given modulating signal amplitude.

Phase modulation and frequency modulation are closely related. In fact, FM can be achieved by first phase-modulating a signal and then passing it through an integrator. Conversely, PM can be achieved by frequency-modulating a signal and then passing it through a differentiator. The primary difference lies in how the modulating signal directly affects the carrier. PM's phase deviation is directly proportional to the modulating signal's amplitude, while FM's frequency deviation is directly proportional to the modulating signal's amplitude.

Phase modulation is used in various communication systems, including some radio broadcasting, satellite communications, and data transmission. Its ability to provide good noise immunity is a significant advantage. However, it can be more complex to implement than AM.