*Question G3B03:
Which frequency will have the least attenuation for long-distance skip propagation?*  

*Correct Answer is  A: Just below the MUF*  

### AI Response: (may contain errors)  

For long-distance skip propagation, the frequency that will have the least attenuation is just below the Maximum Usable Frequency (MUF). Here's why:

1. **Correct Answer: Just below the MUF**
   - The MUF is the highest frequency at which a radio wave can be transmitted between two points via ionospheric reflection. Frequencies just below the MUF are optimal because they are high enough to minimize absorption in the ionosphere but still low enough to be refracted back to Earth. This results in less attenuation and more reliable long-distance communication.

2. **Why the Other Choices are Incorrect:**
   - **Just above the LUF (Lowest Usable Frequency):** Frequencies just above the LUF are often subject to higher levels of ionospheric absorption, leading to greater attenuation and less effective long-distance propagation.
   - **Just below the critical frequency:** The critical frequency is the highest frequency that can be reflected directly back to Earth when transmitted vertically. Frequencies just below this are not optimal for long-distance skip propagation because they may not be refracted back to Earth at the desired distance.
   - **Just above the critical frequency:** Frequencies above the critical frequency will pass through the ionosphere rather than being refracted back to Earth, making them unsuitable for skip propagation.

3. **Useful Rule of Thumb:**
   - For effective long-distance communication, aim to use frequencies just below the MUF. This ensures that the signal is refracted efficiently by the ionosphere with minimal attenuation. 

Understanding these concepts helps in selecting the right frequency for reliable long-distance communication via ionospheric propagation.