There's all kinds of mischief and bullshit going on with meter readings on various people's YouTube channels. You can make a meter read pretty much whatever you want by adjusting it internally.
Also due to the lack of an LPF, those 400 watts includes all the radiation on harmonic frequencies. 400 watt reading DOESN'T mean 400 watts is radiating on the fundamental frequency.
Also due to the lack of an LPF, those 400 watts includes all the radiation on harmonic frequencies. 400 watt reading DOESN'T mean 400 watts is radiating on the fundamental frequency.