*Question G4B07:
What signals are used to conduct a two-tone test?*  

*Correct Answer is  B: Two non-harmonically related audio signals*  

### AI Response: (may contain errors)  

In a two-tone test, the goal is to evaluate the linearity and distortion characteristics of an amplifier or transmitter. Here's why the correct answer is B: Two non-harmonically related audio signals.

### Explanation:

1. **Correct Answer: B - Two non-harmonically related audio signals**
   - **Purpose**: The two-tone test uses two audio signals that are not harmonically related to each other to avoid intermodulation distortion products that could be mistaken for harmonics. This helps in assessing the linearity of the system.
   - **Non-harmonically related**: This means the frequencies of the two tones do not share a common multiple, which ensures that any distortion products are due to the system's non-linearity and not due to the input signals themselves.

2. **Why Other Choices Are Incorrect:**
   - **A: Two audio signals of the same frequency shifted 90 degrees**
     - Using two signals of the same frequency would not provide a meaningful test of linearity, as they would not produce intermodulation products.
   - **C: Two swept frequency tones**
     - Swept frequency tones are used for different types of tests, such as frequency response, but not for evaluating intermodulation distortion.
   - **D: Two audio frequency range square wave signals of equal amplitude**
     - Square waves contain multiple harmonics, which would complicate the analysis of intermodulation distortion, making it difficult to isolate the effects of non-linearity.

### Key Points:
- **Intermodulation Distortion**: The two-tone test is specifically designed to measure intermodulation distortion, which occurs when non-linearities in the system create new frequencies that are combinations of the original tones.
- **Linearity Testing**: By using non-harmonically related tones, any new frequencies generated can be attributed to the system's non-linear behavior, providing a clear indication of its linearity.

This test is crucial for ensuring that transmitters and amplifiers operate efficiently without introducing unwanted signals that could interfere with communication.