*Question G8B12:
What process combines two signals in a non-linear circuit to produce unwanted spurious outputs?*  

*Correct Answer is  A: Intermodulation*  

### AI Response: (may contain errors)  

Intermodulation is the correct answer because it involves the mixing of two or more signals in a non-linear circuit, resulting in the creation of additional signals at frequencies that are combinations of the original frequencies. These additional signals are called intermodulation products and are often unwanted spurious outputs.

### Explanation:

1. **Intermodulation (Correct Answer):**
   - **Non-linear Mixing:** When two or more signals pass through a non-linear device, such as an amplifier operating outside its linear range, new frequencies are generated. These frequencies are sums and differences of the original frequencies and their harmonics.
   - **Example:** If two signals with frequencies $f_1$ and $f_2$ are mixed, intermodulation products can appear at frequencies like $2f_1 - f_2$, $2f_2 - f_1$, $f_1 + f_2$, etc.
   - **Unwanted Outputs:** These products can interfere with other communications and are considered spurious emissions.

2. **Why the Other Choices are Incorrect:**
   - **Heterodyning:** This is a process used in radio receivers to convert a signal to an intermediate frequency by mixing it with a local oscillator. It is a linear process and is used intentionally, not for producing spurious outputs.
   - **Detection:** This refers to the process of extracting information from a modulated carrier wave, such as demodulating an AM signal. It is not related to the creation of spurious signals.
   - **Rolloff:** This term describes the rate at which a filter attenuates a signal beyond its cutoff frequency. It is not related to the mixing of signals or the creation of spurious outputs.

### Key Points:
- **Non-linear Circuits:** Intermodulation occurs in non-linear circuits, which do not maintain a proportional relationship between input and output signals.
- **Spurious Outputs:** These are unwanted signals that can cause interference in communication systems.

Understanding intermodulation is crucial for managing interference and ensuring clean signal transmission in radio communications.