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it really depends on your build, i got 6V in 2 hour of it siting in the room not close to a live AC current. this is a minimum example of potential only, it is influenced by the electrons in the surroundings. for example the fact that the antenna ("aluminum foil") is close to the light from the light-bulb and current in the cable that are connected to AC current, it influences the antenna wirelessly with a type of magnetic pulse from the AC current.it depends on how good you are at tweaking my example ;)
Radiant Energy (Nikola Tesla)