Measuring exact power output can be a costly endeavor. Even something as simple as an RF power meter for measuring the levels of something like a WiFi card can break the bank. But this Wideband RF Power Meter is easy on the pocketbook and versatile too. It can be used to identify the exact output of your QRP rig, but it can also works on other devices.
Programmable oscillators, HamShields, and even Bluetooth Modules work with this meter. It functions like any other serial device. Once you plug it in, simply load your terminal program of choice. The meter will output the power levels in dBm every second and measure power from any frequency between 10MHz and 2700MHz. While the silkscreen does mention 45MHz and above, the seller has done testing to ensure it works below this range.
The simple USB serial functionality makes it easy to take quick measurements. Power levels beyond the +20dBm input can also be measured by using an external attenuator. The chip is primarily flat across the 39-2700MHz range, but each power meter also includes a calibration table for making corrections on specific frequency ranges down to 10MHz.
The Wideband RF Power meter is also open hardware and open software. The seller includes documentation and source code links on the product page.