E9A08: Frequency band has the smallest first Fresnel zone

Q: Which frequency band has the smallest first Fresnel zone?

The correct answer is A: 5.8 GHz. The correct answer is A: 5.8 GHz. The frequency band with the smallest first Fresnel zone is 5.8 GHz. The Fresnel zone size is inversely proportional to frequency - higher frequencies have smaller Fresnel zones. The first Fresnel zone is an elliptical region between transmitter and receiver that must be clear of obstructions for optimal signal propagation. The radius of the first Fresnel zone is proportional to the square root of (distance × wavelength). Since wavelength = speed of light / frequency, higher frequencies have shorter wavelengths, resulting in smaller Fresnel zones. At 5.8 GHz (the highest frequency listed), the wavelength is shortest, so the Fresnel zone is smallest. This is important for microwave communications where Fresnel zone clearance is critical.

Updated: Dec 9, 2025 | Source: 2024-2028 Question Pool | Topic: E9A

E9A08E9A

Which frequency band has the smallest first Fresnel zone?

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Deep Dive: E9A08

The correct answer is A: 5.8 GHz. The frequency band with the smallest first Fresnel zone is 5.8 GHz. The Fresnel zone size is inversely proportional to frequency - higher frequencies have smaller Fresnel zones. The first Fresnel zone is an elliptical region between transmitter and receiver that must be clear of obstructions for optimal signal propagation. The radius of the first Fresnel zone is proportional to the square root of (distance × wavelength). Since wavelength = speed of light / frequency, higher frequencies have shorter wavelengths, resulting in smaller Fresnel zones. At 5.8 GHz (the highest frequency listed), the wavelength is shortest, so the Fresnel zone is smallest. This is important for microwave communications where Fresnel zone clearance is critical.

Why Other Answers Are Wrong

Option B: Incorrect. 3.4 GHz has a longer wavelength than 5.8 GHz, so it has a larger Fresnel zone, not smaller. Option C: Incorrect. 2.4 GHz has an even longer wavelength, resulting in a larger Fresnel zone than 5.8 GHz. Option D: Incorrect. 900 MHz has the longest wavelength of the options, so it has the largest Fresnel zone, not the smallest.

Exam Tip

Smallest Fresnel zone = Highest frequency. Remember: Higher frequencies have smaller Fresnel zones. 5.8 GHz (highest) has the smallest Fresnel zone.

Memory Aid

**S**mallest **F**resnel **Z**one = **H**ighest **F**requency (think 'SFZ = HF', 5.8 GHz)

Real-World Example

You're setting up a 5.8 GHz microwave link. The first Fresnel zone is very small (maybe a few feet in radius), so you need precise clearance of obstructions. At 900 MHz, the Fresnel zone would be much larger (maybe 20-30 feet), requiring more clearance. The higher frequency means a smaller Fresnel zone that's easier to clear but more sensitive to obstructions.

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E9A

Reference: FCC Part 97.3

Key Concepts

Fresnel zone Frequency Wavelength Microwave propagation

Verified Content

Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9A topic.