*Question T7A08:
Which of the following describes combining speech with an RF carrier signal?*  

*Correct Answer is  C: Modulation*  

### AI Response: (may contain errors)  

To understand the question about combining speech with an RF carrier signal, we need to focus on the concept of modulation.

### Correct Answer: C: Modulation

- **Why Modulation is Correct:**
  - Modulation is the process of varying one or more properties of a carrier signal (such as amplitude, frequency, or phase) in accordance with the information signal (in this case, speech). 
  - This allows the speech signal to be transmitted over radio frequencies, making it suitable for communication over long distances.

### Why the Other Choices are Incorrect:

- **A: Impedance matching**
  - Impedance matching refers to the process of making the impedance of a load (like an antenna) equal to the impedance of the source (like a transmitter) to maximize power transfer. It does not involve combining speech with a carrier signal.

- **B: Oscillation**
  - Oscillation refers to the repetitive variation, typically in time, of some measure (like voltage or current). While oscillators generate RF signals, they do not specifically describe the process of combining speech with a carrier.

- **D: Low-pass filtering**
  - Low-pass filtering is a technique used to allow signals with a frequency lower than a certain cutoff frequency to pass through while attenuating higher frequencies. This is not related to the process of combining speech with an RF carrier.

### Summary

In summary, modulation is the key process that allows speech to be combined with an RF carrier signal for effective transmission. Understanding this concept is crucial for the Extra Class exam.