Principles of Communication Angle Modulation
Difference: * In PM, phase of carrier signal changes while in FM frequency of carrier signal changes in accordance In Phase Modulation, modulation index is directly proportional to modulating vo. Related Questions (More Answers Below). THe frequency in phase modulation does change but not directly like in FM on the difference between FM and PM and their relationship. Know the relationship of carrier frequency, modulation frequency and vary one of the three parameters of the signal: amplitude, frequency or phase. Therefore.
Note that — unlike an AM wave — the FM wave doesn't have a single frequency value. This makes an FM wave obviously different to an AM one. The instantaneous phase of the modulated wave at any instant can be obtained by substituting The instantaneous frequency of the PM wave will therefore be Comparing In both cases the wave's frequency and phase vary from moment to moment.
The only difference is that one corresponds to a modulation pattern which is the differential of that produced by the other. This range is usually described in terms of the modulated signal's peak frequency deviation value, defined as since it indicates the largest swing or deviation in frequency either side of. Note that its value depends upon the magnitude of the modulation,but not upon the modulating frequency. However we often need to know the frequency spectrum of the modulated wave — for example, in order to be able to determine the bandwidths of any filters, amplifiers, etc that we require.
By consulting a good maths textbook we can discover that this expression can after some boring algebra! The sinewave modulated AM signal has only three spectral components, at the frequencies.
Frequency Modulation, Phase Modulation, and FM spectra
The FM wave has spectral components at all the frequencies,where n can be any integer from to. This result is rather startling since it means that, strictly speaking, a system has to provide an infinite bandwidth to carry an accurate FM or PM signal! The deviation of the frequency of the carrier signal from high to low or low to high can be termed as the Carrier Swing.
The modulation index is small. This is used in mobile communications such as police wireless, ambulances, taxicabs, etc. The modulation index is large, i. Its spectrum consists of a carrier and infinite number of sidebands, which are located around it. This is used in entertainment broadcasting applications such as FM radio, TV, etc.
Assignment Questions - _
Phase Modulation In frequency modulation, the frequency of the carrier varies. But in Phase Modulation PMthe phase of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal. The amplitude and the frequency of the carrier signal remains constant whereas the phase of the carrier changes. The phase of the modulated wave has got infinite points where the phase shift in a wave can take place. The instantaneous amplitude of the modulating signal, changes the phase of the carrier.
When the amplitude is positive, the phase changes in one direction and if the amplitude is negative, the phase changes in the opposite direction.
The frequency of the wave also changes the phase of the wave. Though they are related, their relationship is not linear. Phase modulation is an indirect method of producing FM.