*Question G8A04:
What emission is produced by a reactance modulator connected to a transmitter RF amplifier stage?*  

*Correct Answer is  B: Phase modulation*  

### AI Response: (may contain errors)  

A reactance modulator is a device used to vary the reactance in a circuit, which in turn changes the phase of the signal. This is a key component in generating phase modulation (PM).

### Explanation:

1. **Correct Answer: Phase Modulation (PM)**
   - A reactance modulator changes the reactance in the circuit, which directly affects the phase of the carrier signal. This results in phase modulation, where the phase of the carrier wave is varied in accordance with the modulating signal.

2. **Why Other Choices Are Incorrect:**
   - **A: Multiplex Modulation**
     - Multiplexing is a technique used to combine multiple signals into one. It is not a type of modulation produced by a reactance modulator.
   - **C: Amplitude Modulation (AM)**
     - Amplitude modulation involves varying the amplitude of the carrier signal, not the phase. A reactance modulator does not affect amplitude.
   - **D: Pulse Modulation**
     - Pulse modulation involves modulating a signal by varying the width, position, or amplitude of pulses. This is unrelated to the phase changes produced by a reactance modulator.

### Useful Concept:

- **Phase Modulation (PM)**
  - In PM, the phase of the carrier signal is varied in proportion to the instantaneous amplitude of the modulating signal. This can be expressed as:
  $$ \phi(t) = \phi_0 + k_p \cdot m(t) $$
  where:
  - $\phi(t)$ is the instantaneous phase.
  - $\phi_0$ is the initial phase.
  - $k_p$ is the phase sensitivity.
  - $m(t)$ is the modulating signal.

Understanding how a reactance modulator affects the phase of a signal helps clarify why phase modulation is the correct answer.