Question T9B05
From subelement T9 - T9B
What happens as the frequency of a signal in coaxial cable is increased?
Why is this correct?
The loss increases (D) because coaxial cable has frequency-dependent losses that worsen at higher frequencies. This occurs due to skin effect, where current concentrates near conductor surfaces at higher frequencies, and dielectric losses in the cable insulation that increase with frequency. Options A and C are wrong because characteristic impedance is determined by the physical construction of the cable and remains constant regardless of frequency.
Memory tip
Remember the pattern: frequency and loss always move together in the same direction for transmission lines. Higher frequency always means higher loss. This relationship holds true across all types of coax and helps explain why VHF/UHF applications often require special low-loss cables or hardline.
Learn more
This frequency-dependent loss explains why satellite dishes place amplifiers directly at the antenna rather than at the receiver, and why repeater installations use expensive air-insulated hardline for VHF/UHF operations. The skin effect causes RF current to flow only in a thin layer near conductor surfaces at higher frequencies, effectively reducing the conductor's cross-sectional area. Additionally, dielectric heating in the cable's insulation increases proportionally with frequency, converting more transmitted power to waste heat.
Think about it
Why do you think microwave communication systems often use waveguides instead of coaxial cable at very high frequencies?