1. Lecture 8:
PM Modulation
1st semester
By: Elham Sunbu

2. OUTLINES:
PM Modulation
Angle Modulation

3. PM Modulation
- In phase modulation (PM), the carrier signal changes its phase with the changes in the message signal amplitude.
- FM and PM are types of what is called Angle modulation.

4. Phase Shift
- A begins its cycle and reaches its peak before wave B, it is said to lead wave B.
Wave  C, on the other hand, lags wave B by 30 degrees.

5. PM Modulation
- FM and PM are interrelated; one cannot change without the other changing.
- In FM, the frequency of a carrier signal deviates from its center frequency by an amount that is proportional to the message signal amplitude.
- In PM, the frequency (and phase) of a carrier signal changes by an amount that is proportional to the message signal amplitude and frequency.

6. PM Modulation
- FM requires the carrier’s frequency to deviate both above and below its center frequency.
- During the process of frequency modulation, the peaks of each successive cycle in the FM modulated waveform occur at times other than they would if the carrier were un modulated.
- This is actually an incidental phase shift that takes place along with the frequency shift in FM.

7. PM Modulation
- Just the opposite action takes place in phase modulation.
- Notice that the time period of each successive cycle varies in the modulated wave according to the audio-wave variation.
- Since frequency is a function of time period per cycle, we can see that such a phase shift in the carrier will cause its frequency to change.

8. PM Modulation
- In Frequency modulation, the frequency of a carrier signal deviates from its center frequency by an amount that is proportional to the message signal amplitude.
- FM uses the message signal, m(t), to vary the carrier frequency within some small range about its original value.

9. PM and FM - PM is similar to FM.
- When the instantaneous phase of a carrier is varied, the instantaneous frequency changes as well.
- When the instantaneous frequency is varied, the instantaneous phase changes.

10. PM and FM
- But PM and FM are not exactly equivalent, especially in analog applications.
- When an FM receiver is used to demodulate a PM signal, or when an FM signal is intercepted by a receiver designed for PM, the audio is distorted.
- This is because the relationship between phase and frequency variations is not linear ; that is, phase and frequency do not vary in direct proportion.

11. PM and FM
- The basic difference between FM & PM lies in which property of the carrier is directly varied by modulating signal.
- In FM, the frequency of carrier is varied directly.
- In PM, phase of the carrier is varied directly.
- The frequency change in FM is vital, but in PM it is merely incidental.
- In PM, only the phase shift is important.

12. PM and FM
- Unlike FM, PM is not widely used for transmitting radio waves.
- This is because PM requires more complex receiving hardware.

13. Thank You