Even the simplest wattmeter is better than no wattmeter. Following this sentence I built a very simple wattmeter based on schematic of SWR meter developed and published in the Internet by JA6HIC. Using a forward only part of the schematics I soldered quite precise instrument which allows to measure RF power from tenths of mW up to 5W. Input impedance is 50 ohms as well as output impedance. Don't ask me how it works. It just shows a power. I used K-1 for calibration scales.
Schematics of VSW ( very simple wattmeter)
Alignment of VSW
1. Find the accurate source of the RF signal which provides at least 5W with increments ( I used K-1)
2. Set a FSD ( full scale deflection) at 5W on highest HF frequency and mark on the scales
3. Repeat marking decreasing power
4. Set capacitor trimmer 100pF to minimalise frequency effect on reading, starting from highest frequency ( it was 21 MHz in my project)
5. Accept the fact that error of measurement is highest on the beginning of the scales
6. Build "pixie" immediately :'-)))
Wattmeter assembled on 06.01.2003
Construction details - inductance and coupler made of piece of RG-213
This nice looking setup weights approx. 1lbs
I measured "Forty-Oner"
and the output power was 0,8W on dummy load and 1W on 3 element beam with RG-213/U feeder.