The RS-WM1 2 channel RF Wattmeter Arduino Shield provides precision analog reference voltage to an Arduino and connections for a 16x2 Character LCD. Add attenuators and directional couplers for extended range and SWR measurements.
Frequency: 1 - 500MHz
Range: 0.1mW - 2W
Accuracy: 0.3 dB with calibration
Check out the RS-WM1 tech site for details on how to build your wattmeter including access to download the Arduino sketch.
Directional coupler board
Arduino Touch Screen shield