*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)  

The correct answer to the question about the signals used to conduct a two-tone test is:

**B: Two non-harmonically related audio signals.**

### Explanation of the Correct Answer:
- **Two non-harmonically related audio signals** are used in a two-tone test to evaluate the linearity and performance of an amplifier or transmitter. These signals are typically at different frequencies that do not have a simple harmonic relationship (e.g., one frequency is not an integer multiple of the other). This allows for the observation of intermodulation distortion and other nonlinear effects in the system.

### Why the Other Choices are Incorrect:
- **A: Two audio signals of the same frequency shifted 90 degrees**  
  This choice describes a phase shift rather than two distinct frequencies. A two-tone test requires two different frequencies to assess the system's response to multiple signals.

- **C: Two swept frequency tones**  
  Swept frequency tones involve varying the frequency over a range, which is not the same as using two fixed, distinct frequencies. The two-tone test specifically uses two stable frequencies to analyze intermodulation products.

- **D: Two audio frequency range square wave signals of equal amplitude**  
  While square waves can be used in testing, the two-tone test specifically requires sine waves (or similar continuous waveforms) to accurately assess linearity and distortion. Square waves introduce additional harmonics that complicate the analysis.

### Useful Concepts:
- **Intermodulation Distortion (IMD)**: This is a key metric evaluated during a two-tone test. It occurs when two signals interact in a nonlinear system, producing additional frequencies that are not present in the original signals.
- **Frequency Separation**: The two frequencies used in the test should be sufficiently separated to avoid overlap in their harmonic content, which helps in clearly identifying distortion products.

In summary, the two-tone test is a critical method for assessing the performance of RF amplifiers and transmitters, and it relies on the use of two distinct, non-harmonically related audio signals.