*Question G8B11:
What combination of a mixer’s Local Oscillator (LO) and RF input frequencies is found in the output?*  

*Correct Answer is  C: The sum and difference*  

### AI Response: (may contain errors)  

In a mixer, the output frequencies are the result of combining the Local Oscillator (LO) frequency and the Radio Frequency (RF) input frequency. The key operation of a mixer is to produce new frequencies by adding and subtracting these two frequencies.

1. **Correct Answer: The sum and difference**

   - **Explanation**: A mixer generates two primary output frequencies:
     - The **sum** of the LO and RF frequencies: $f_{\text{sum}} = f_{\text{LO}} + f_{\text{RF}}$
     - The **difference** of the LO and RF frequencies: $f_{\text{diff}} = |f_{\text{LO}} - f_{\text{RF}}|$
   - These frequencies are used in various applications, such as frequency conversion in receivers.

2. **Why the other choices are incorrect**:

   - **A: The ratio**: Mixers do not produce a frequency that is the ratio of the LO and RF frequencies. Ratios are not relevant to the mixing process.
   
   - **B: The average**: Mixers do not output the average of the LO and RF frequencies. The average would be calculated as $\frac{f_{\text{LO}} + f_{\text{RF}}}{2}$, which is not a function of a mixer.
   
   - **D: The arithmetic product**: Mixers do not output the product of the LO and RF frequencies. The product would be $f_{\text{LO}} \times f_{\text{RF}}$, which is not a typical result of mixing.

In summary, mixers are designed to output the sum and difference of the input frequencies, which is essential for frequency translation in radio systems.