Where Is Fading Most Severe? Horizon, Shadow Zone, and Good Optical Paths Consider the statements: Fading of signals is generally greatest near the radio horizon. Fading of signals is generally greatest in the shadow zone. Fading is small when a good optical path is present. Which statements are correct?

Introduction / Context:
In terrestrial and over-the-horizon links, fading arises from multipath, diffraction, and atmospheric refractivity changes. The severity of fading depends strongly on geometry: whether the receiver is near the radio horizon, in a diffraction shadow, or has a clear line-of-sight optical path.

Given Data / Assumptions:

• Standard atmosphere with typical refractivity gradients.
• Frequency in VHF/UHF/microwave where multipath and ducting can occur.
• “Good optical path” implies clear, unobstructed line-of-sight with strong direct component.

Concept / Approach:

Near the radio horizon, the direct ray skims the Earth and becomes comparable in strength to refracted or reflected rays, increasing the chance of deep interference fades. In shadow zones, the signal relies on diffraction or scattered components that are highly variable, so fading can be severe. Conversely, a high-clearance, good optical path yields a dominant direct ray and weaker multipath, so fading depth is reduced.

Step-by-Step Solution:

Verification / Alternative check:

Link planning tools and ITU-R recommendations show larger fade margins required for paths near the horizon or with obstacles, and smaller margins for clear, elevated LOS paths.

Why Other Options Are Wrong:

Any subset that omits one of the three truths fails to capture the complete behavior across these scenarios.

Common Pitfalls:

Equating “radio horizon” with no signal; in practice, ducting or reflection may intermittently enhance or depress signals, producing strong fades.

Final Answer:

1, 2 and 3