T9B05: What happens as the frequency of a signal in coaxial cable is increased

Q: What happens as the frequency of a signal in coaxial cable is increased?

The correct answer is D: The loss increases. The correct answer is D: The loss increases. As the frequency of a signal in coaxial cable is increased, the loss increases. Higher frequencies experience more loss in coaxial cable due to skin effect (current flows near the surface of conductors at high frequencies) and dielectric losses. This is why low-loss cable is important for VHF/UHF operation. For amateur radio operators, understanding frequency-dependent loss helps explain why feed line selection matters more at higher frequencies and why shorter feed lines are often used for VHF/UHF.

Updated: Dec 9, 2025 | Source: 2022-2026 Question Pool | Topic: T9B

T9B05T9B

What happens as the frequency of a signal in coaxial cable is increased?

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Deep Dive: T9B05

The correct answer is D: The loss increases. As the frequency of a signal in coaxial cable is increased, the loss increases. Higher frequencies experience more loss in coaxial cable due to skin effect (current flows near the surface of conductors at high frequencies) and dielectric losses. This is why low-loss cable is important for VHF/UHF operation. For amateur radio operators, understanding frequency-dependent loss helps explain why feed line selection matters more at higher frequencies and why shorter feed lines are often used for VHF/UHF.

Why Other Answers Are Wrong

Option A: Incorrect. Characteristic impedance doesn't decrease with frequency - it's determined by the cable's physical construction (conductor size, dielectric), not frequency. Option B: Incorrect. Loss doesn't decrease with frequency - it increases. Higher frequencies have more loss due to skin effect and dielectric losses. Option C: Incorrect. Characteristic impedance doesn't increase with frequency - it's constant, determined by cable construction.

Exam Tip

Higher frequency = more loss in coax. Think 'H'igher 'F'requency = 'H'igher 'F'eed line loss. Skin effect and dielectric losses increase with frequency. Impedance stays constant, but loss increases.

Memory Aid

Higher frequency = more loss. Think 'H'igher 'F'requency = 'H'igher loss. Skin effect and dielectric losses increase with frequency. Impedance stays constant (50 ohms), but loss increases significantly.

Real-World Example

You use the same RG-58 cable for 2 meters (146 MHz) and 70 cm (440 MHz). At 2 meters, you might have 2 dB loss per 100 feet. At 70 cm, the same cable has about 4 dB loss per 100 feet - double the loss. This is why low-loss cable is especially important for UHF operation, and why feed lines are often kept short at higher frequencies.

Source & Coverage

Question Pool: 2022-2026 Question Pool

Subelement: T9B

Reference: 2022-2026 Question Pool · T9 - Antennas and feed lines

Key Concepts

Coaxial cable loss Frequency-dependent loss Feed line losses High frequency losses

Verified Content

Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T9B topic.