Question T5C05
From subelement T5 - T5C
What is the unit of impedance?
Why is this correct?
Impedance is the opposition to AC current flow, and like resistance (which opposes DC current), it's measured in ohms (Ω). While resistance only applies to DC circuits, impedance combines both resistance and reactance to give the total opposition to alternating current. Volts measure electrical pressure, amperes measure current flow, and coulombs measure electrical charge—none of these describe opposition to current flow.
Memory tip
Remember that any measure of opposition to electrical flow uses ohms as the unit. Whether it's resistance (DC opposition), reactance (frequency-dependent AC opposition), or impedance (total AC opposition), they all share the same unit. This pattern appears throughout electronics.
Learn more
In practical amateur radio operation, impedance matching is critical for efficient power transfer. Most amateur transceivers and coaxial cables are designed for 50-ohm systems. When impedances don't match—like connecting a 75-ohm antenna to a 50-ohm radio—power transfer becomes inefficient and some energy reflects back toward the source. This impedance mismatch can reduce transmitted power and potentially damage equipment, which is why antenna tuners and proper system design focus on maintaining consistent impedance throughout the RF path.
Think about it
Why do you think amateur radio systems standardize around 50-ohm impedance rather than some other value like 75 ohms or 300 ohms?