Hello
Back in the 60s I did a lot of SWL (shortwave listening), and my antennas were all "long wire". I strung them everywhere in all lengths and all types of wire.
Frequently these antenna gave me "jolts" that left lasting impressions!
We didn't have DVMs or LEDs to check for voltage, but we did have neon lamps. It wasn't uncommon to put a neon lamp across the ground and antenna at the receiver to help cut down on noise. Sometimes between the "stray voltage" on the antenna and the floating chassis (an old TUBE Hallcrafters SuperSky Rider) was a BAD mix along all the other (mom and dad called it crap)Radios, transmitters,signal tracers,RF generators,AF generators,Sillyscopes,tube testers, more radios, VTVMs and stuff I can no longer remember that was on my desk. Touching the wrong combination and you were sitting on the floor with curly hair.
As long as the wire isn't "transmitting" RF I don't think that the FCC would care what you're doing. As long as the wire is below the local airport height maximum (I recall something about over 75 feet needing a beacon) the FAA wouldn't care.
With all that said, yes depending whats near by and the transmitted RF (both frequency and output power and near by power transmission lines (voltage and current)
You can "harvest" plenty of voltage on a "long wire". How much could be VERY unpredictable and might even be dangerous, for example...
Back in the early 70s I worked at furniture factory. It was in a very old four story building. On the roof was a "huge" dust collection system run by an 100hp motor (fan about 15ft di.) There was a steel cable (1/4 or 3/8in di) that ran from the blower on the roof to the first floor. The cable allowed the people on the first floor to open/close a damper. One day a fire broke out on the second floor. Turns out that the steel cable had enough current inducted into it that caused a arc from the cable to the wooden floor to a fire sprinkler pipe. It was the addition of a large bull planer (drawing more current on a power buss) that turned an 100 year old system into a fire hazard.
Yes, it could work but how one would regulate the power could drive a person to drink.
I think you'd be dealing with high voltage, but very low current.
There are LOTS of stories of "stay voltages" causing "issues" for live stock and people.
AX7
Mark
p.s. don't forget to wrap your head with foil when using your cell phone!