The difference between phase and frequency modulation

Options

A. practically they are same but theoretically they differ
B. lies in the poorer audio response of phase modulation
C. lies in the poorer audio response of frequency modulation
D. lies in the definitions of mudulation and their modulation index

Answer

### Step-by-Step Text Solution:

1. **Definition of Modulation**:
- Modulation is the process of varying one or more properties of a periodic waveform, known as the carrier signal, with a modulating signal that contains the information to be transmitted.

2. **Angle Modulation**:
- Both phase modulation (PM) and frequency modulation (FM) are types of angle modulation. In angle modulation, the angle of the carrier wave is varied in accordance with the modulating signal.

3. **Phase Modulation (PM)**:
- In phase modulation, the phase of the carrier signal is varied in proportion to the instantaneous amplitude of the modulating signal. The frequency remains constant, but the phase shifts according to the information signal.

4. **Frequency Modulation (FM)**:
- In frequency modulation, the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal. The phase changes as a result of the frequency variation, but the amplitude of the carrier remains constant.

5. **Key Differences**:
- **Nature of Variation**:
- In PM, the phase is varied while the frequency remains constant.
- In FM, the frequency is varied while the phase changes as a result.
- **Response to Input Signal**:
- PM responds to changes in the amplitude of the modulating signal by changing the phase.
- FM responds to changes in the amplitude of the modulating signal by changing the frequency.

6. **Practical Similarities**:
- Practically, PM and FM can appear similar in terms of their output waveforms and their effects on the transmitted signal. However, they are fundamentally different in their theoretical basis.

7. **Conclusion**:
- While both phase and frequency modulation are types of angle modulation and can be used for similar applications, they differ in how they manipulate the carrier wave. Understanding these differences is crucial for applications in communication systems.