RF Power Meters vs. Field Strength Meters: What’s the Difference?

When it comes to measuring radio signals, two tools often get mentioned in the same breath: the RF power meter and the field strength meter. They sound similar, but they serve very different purposes.

An RF power meter is all about what’s happening inside the shack. Hooked inline between your transmitter and antenna system, it tells you how much power your rig is actually putting out. That’s important not just for bragging rights—though every ham likes to see a solid 100 watts—but for checking efficiency, tuning amplifiers, or verifying that your feedline isn’t eating half your signal. Many power meters also show SWR (standing wave ratio), giving you insight into how happy your antenna system really is.

Surecom SW102 Display: Watts, Frequency, Forward & Reverse Power, Efficiency, and SWR

Now, a field strength meter looks outward instead of inward. It measures how much of that signal is actually being radiated into the environment. Think of it as standing outside your station and holding up a hand to feel how strong the signal “feels” in the air. This is incredibly useful when tuning antennas. Move your feedpoint, trim an element, or add a counterpoise—watch the field strength needle jump or dip, and you’ll know instantly which direction you’re heading.

Surecom SS11 Field Strength Meter

In short: power meters measure what your radio delivers, while field strength meters measure what actually gets out. A station could show a healthy 100 watts on the power meter but radiate poorly if the antenna system is mismatched or lossy. On the flip side, even a modest QRP signal can look mighty on a field strength meter if the antenna is well tuned and efficient.

Both tools have their place, but together they give you the full picture—what goes in, and what comes out.

Speaking of SWR -

Sorry, a little math is involved after taking some measurements with your RF power meter. Note the forward power (P_f) and the reflected power (P_r) values. Plug the values into the following formula:

Example: If the output is 100 watts and the reflected power is 5 watts, the SWR is about 1.22 / 0.78 = 1.57 (an acceptable SWR). This is with 5% of power reflected.