What is the lowest limiting frequency for satisfactory sky wave communication known as?

• A. MUF
• B. LUF
• C. Fading
• D. Skip zone

Answer: (B)

The lowest limiting frequency for satisfactory sky wave communication is referred to as the LUF, or Lowest Usable Frequency. This frequency represents the minimum frequency at which a radio wave can successfully be reflected back to Earth by the ionosphere, enabling reliable communication over long distances via sky wave propagation.

At frequencies below the LUF, the radio waves may not adequately refract off the ionosphere and could either penetrate through without returning or suffer significant signal attenuation. This makes communication sporadic or entirely ineffective. Therefore, the LUF is crucial for determining the frequencies that can be used for effective sky wave transmission.

In contrast, concepts such as the MUF, or Maximum Usable Frequency, indicate the highest frequency that can still be reflected by the ionosphere, while fading refers to variations in signal strength due to various atmospheric conditions. The skip zone is a range of distances where radio waves cannot be received due to the lack of enough refraction, which is different from the determination of the lowest usable frequency. Thus, LUF specifically indicates the minimum frequency where propagation is viable, making it the appropriate term for this concept.