*Question G7B11:
For which of the following modes is a Class C power stage appropriate for amplifying a modulated signal?*  

*Correct Answer is  B: FM*  

### AI Response: (may contain errors)  

A Class C power stage is appropriate for amplifying signals that have a constant amplitude, such as FM (Frequency Modulation). Here's why:

1. **Why the correct answer is correct (FM):**
   - Class C amplifiers are highly efficient but introduce distortion. They are suitable for signals where amplitude variations do not carry information, such as FM. In FM, the information is carried by frequency variations, not amplitude, so the distortion introduced by a Class C amplifier does not affect the signal integrity.

2. **Why the other choices are incorrect:**
   - **SSB (Single Sideband):** SSB signals have varying amplitude, which carries the information. A Class C amplifier would distort these amplitude variations, making it unsuitable for SSB.
   - **AM (Amplitude Modulation):** AM signals also rely on amplitude variations to convey information. Using a Class C amplifier would distort these variations, leading to significant signal degradation.

3. **Useful formulas or rules of thumb:**
   - Class C amplifiers are typically used for:
     - FM signals
     - CW (Continuous Wave) signals, where the carrier is constant
   - They are not suitable for amplitude-sensitive modes like AM and SSB due to their inherent distortion of amplitude variations.

In summary, Class C amplifiers are efficient and suitable for constant-amplitude signals like FM, but not for modes like SSB and AM that rely on amplitude variations to convey information.