*Question G8A02:
What is the name of the process that changes the phase angle of an RF signal to convey information?*  

*Correct Answer is  B: Phase modulation*  

### AI Response: (may contain errors)  

The correct answer to the question is **Phase modulation**.

1. **Why the correct answer is correct:**
   - Phase modulation (PM) is a technique used in communication systems where the phase of a carrier wave is varied in accordance with the information signal. This allows the transmission of data by changing the phase angle of the RF signal, which is essential for conveying information in various types of communication systems, including digital and analog transmissions.

2. **Why the other choices are incorrect:**
   - **A: Phase convolution**: This term is not commonly used in the context of RF signal modulation. Convolution generally refers to a mathematical operation used in signal processing, not a method of conveying information through phase changes.
   - **C: Phase transformation**: This term does not specifically refer to a method of modulation. It may imply a change in phase but lacks the context of conveying information through modulation techniques.
   - **D: Phase inversion**: While phase inversion refers to a 180-degree phase shift, it is not a modulation technique. It is more of a specific operation that can be used in certain applications but does not convey information in the way phase modulation does.

3. **Useful formulas or rules of thumb:**
   - In phase modulation, the phase of the carrier signal can be expressed as:
     $$ 
     \phi(t) = \phi_0 + k_p m(t) 
     $$
     where:
     - $\phi(t)$ = phase of the modulated signal at time $t$
     - $\phi_0$ = initial phase
     - $k_p$ = phase sensitivity (radians per unit of message signal)
     - $m(t)$ = message signal (information to be transmitted)

This formula illustrates how the phase of the carrier signal is altered based on the input message signal, which is the essence of phase modulation.