I would like to build my own HF (1.8 - 30 MHz) SWR meter, however I'm not sure how I can calibrate the meter without an accurate power source. I'm targeting a power capacity of 150 W so I can use it with my HF radio. However, my test equipment at hand does not include a directional wattmeter, and I wouldn't trust the power meter on my radio when the radio is turned off.
I have a number of precision RF sources, but most of those don't exceed 1W in output power. I can get a good 100W+ 50Ω load, spectrum analyzers, and oscilloscopes, but nothing that I would really consider "power RF".
Can I calibrate or validate my meter without an accurate power source or accurate directional wattmeter?