Question T7C08
From subelement T7 - T7C
Which instrument can be used to determine SWR?
Why is this correct?
A directional wattmeter is correct because it measures both forward power (going to the antenna) and reflected power (bouncing back), which are the two values needed to calculate SWR. The other options cannot measure RF power flow: voltmeters measure voltage, ohmmeters measure resistance, and iambic pentameter is a poetry meter (clearly a joke answer). The wattmeter must be installed in the feed line between transmitter and antenna to accurately measure power in both directions.
Memory tip
Look for instruments that measure power flow or direction when SWR questions appear. SWR fundamentally involves comparing forward versus reflected power, so only power-measuring devices work. Regular electrical meters like voltmeters and ohmmeters measure static values, not RF power flow.
Learn more
In amateur radio practice, directional wattmeters serve dual purposes beyond SWR calculation. They help establish proper emission standards compliance by measuring actual radiated power, assist in antenna system troubleshooting by identifying reflection points, and verify frequency privileges are being used at appropriate power levels. Professional installations often use inline directional couplers for continuous monitoring, while portable wattmeters help field operations verify system performance.
Think about it
Why do you think a directional wattmeter needs to measure power flowing in both directions to determine impedance matching, rather than just measuring the total power present?