Question

Waves of UHF frequency are generally transmitted as

• A. ground waves
• B. sky waves
• C. surface waves
• D. space waves

Hint:

A simple frequency guide for propagation modes: - **Low Frequencies (kHz - ~2 MHz):** Ground Wave (e.g., AM Radio) - **Medium Frequencies (~2 MHz - 30 MHz):** Sky Wave (e.g., Shortwave Radio) - **High Frequencies (>30 MHz):** Space Wave (e.g., FM Radio, TV, Mobile Phones)

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Radio waves can propagate from a transmitting antenna to a receiving antenna through different modes, depending on their frequency. The main modes are ground wave, sky wave, and space wave propagation.
Step 2: Detailed Explanation:
- Ground waves (or surface waves): These waves follow the curvature of the Earth. This mode is effective for low frequencies (up to about 2 MHz). As frequency increases, the attenuation by the ground becomes very high.
- Sky waves: These waves are reflected back to Earth by the ionosphere. This mode is effective for frequencies in the range of about 2 MHz to 30 MHz. Frequencies higher than this range usually penetrate the ionosphere and are not reflected back.
- Space waves: These waves travel in a straight line from the transmitter to the receiver. This is known as line-of-sight (LOS) communication. This mode is used for very high frequencies (VHF), ultra-high frequencies (UHF), and microwaves (frequencies above 30 MHz). Since these waves travel in straight lines, the curvature of the Earth limits the communication range. TV broadcast and satellite communication use this mode.
UHF (Ultra High Frequency) ranges from 300 MHz to 3 GHz. These frequencies are too high to be reflected by the ionosphere and are heavily attenuated as ground waves. Therefore, they must be transmitted as space waves.
Step 3: Final Answer:
Waves of UHF frequency are transmitted via line-of-sight, which is known as space wave propagation. Therefore, option (D) is correct.