*Question T9B02:
What is the most common impedance of coaxial cables used in amateur radio?*  

*Correct Answer is  B: 50 ohms*  

### AI Response: (may contain errors)  

The most common impedance of coaxial cables used in amateur radio is 50 ohms. Here's why:

1. **Why the correct answer (50 ohms) is correct:**
   - 50-ohm coaxial cable is widely used in amateur radio because it provides a good balance between power handling capability and signal loss. This impedance is optimal for transmitting RF (radio frequency) signals, making it suitable for most amateur radio applications.

2. **Why the other choices are incorrect:**
   - **A: 8 ohms**: This impedance is typically used for low-power applications, such as speaker connections, and is not suitable for RF transmission.
   - **C: 600 ohms**: This impedance is commonly used in professional audio and some telecommunications applications, but it is not practical for RF transmission in amateur radio.
   - **D: 12 ohms**: This is not a standard impedance for coaxial cables and is not used in any common RF applications.

3. **Useful formulas or rules of thumb:**
   - When selecting coaxial cable, consider the following:
     - For most amateur radio applications, use 50-ohm coax for transmitting and receiving RF signals.
     - For specific applications like balanced lines (e.g., certain antennas), 300-ohm twin-lead may be used, but this is not coaxial cable.

In summary, 50-ohm coaxial cable is the standard for amateur radio due to its efficiency in handling RF signals, while the other options are either too low or not suitable for RF applications.