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You likely aren’t going to get enough energy to make up for the losses incurred when boosting voltage to 4.2 volts or whatever your battery requires. There’s tons and tons of scam devices out there in the world that attempt to convince people these devices make sense, but they really aren’t usable for anything meaningful.

Charging a battery with a couple microamps per hour. Would probably negates things like self-discharge? But certainly wouldn’t recharge a battery that you have in use with a device. And if that device has radio or storage attached to it, you definitely aren’t gaining enough electricity.

@drdabbles @rarely

A few years back some farmer living in Droitwich, England (where the Radio 4 longwave transmitter is situated) lit his barn by connecting an antenna to fluorescent light tubes.

It worked, but also created a "not-spot" in the radio reception which the BBC really didn't like (its part of critical national infrastructure!) - officers from Ofcom turned up at his door, made him take the lot down and ordered him to use more "normal" power sources..

I’m skeptical of the “not-spot” claims here. This would suggest that radios also create “not-spots” when being tuned to as well, or that somehow the florescent light tubes were able to “pull” more electrons from the air that were destined to other radios.

@rarely a radio receiver uses *much* less of the power than lighting up the fluorescent tubes would (it wasn't just one lamp) and this incident happened close enough to the TX that it could upset the SWR of the transmitter output stages - if it /was/ possible to do this without creating problems elsewhere then every tall transmission tower would use the RF to power their aircraft warning lamps rather than a separate power supply...

That is the most plausible explanation I have heard but I still have questions. Say there’s an MW tower down the road and I have a 160m tower in my backyard. If I understand correctly, my tower may cause the signal coming from the AM tower to be re-resonated back to the AM tower so the AM tower needs to be detuned. But say I want to harvest the signal and I have tuned my tower to be resonant with the AM tower. Maybe in this case the SWR reading at the AM station is different because it is getting some of that re-radiated power back, and maybe the radiation pattern of the am station has changed slightly, but wouldn’t the main AM tower cover any gaps just like how waves spread out in the double slit experiment once they hit my resonant tower?

I get that a tower excites another tower, and I can understand that the AM engineers will likely hate me, but I don’t understand how radio reception could be affected. If anything, I might have made the station more directional (like a reflector in a yagi) but probably not.

@rarely if you are /that/ close to the antenna an extra tower, or any large amount of metal making the station more directional will definitely be unwanted, both by tradio station engineers and the Communications Ministry (licenses often require a particular directional pattern). But this is more an issue with LF and MF where waves are larger. At UHF/SHF frequencies for wifi harvesting could work but at present the component count required makes it less viable than other power sources.

It may surprise you to know that in the US as a ham, I have the legal right to hoist an antenna or build a tower so long as it doesn’t fall on a power line.

But even then, I don’t think this setup will create nulls. Say the antenna is 400 meters away which I think is still in the far field but I could be wrong. Even if I erected an almost resonant tower (160m) and assuming the regulatory bodies gave me the permit to do so, assuming it’s not powered and simply is resonant, maybe the radiation pattern changes but not so dramatically that my neighbors on the opposite side of my antenna (from the tower) will get poor reception.

Is the direction of the radiation pattern changing what was meant by the “not-spots”?

@rarely the historical reports of issues I've read about are from mid-late 20th century in areas near high power LF/MF stations that would be in the nearfield - from the Wiki article

> absorption of radiation in the near field by adjacent conducting objects detectably affects the loading on the signal generator (the transmitter).

so it would be noticeable, and viewed as an undesirable thing. Harvesting (small) amounts of power in the far field would not cause issues.

@rarely the claims of "poor reception" caused by "large scale" nearfield power harvesting are from Communications Ministry officers from some decades ago (I mistakenly referred to modern Ofcom rather than the British Post Office which investigated these things until the 1980s), it is possible they just wanted to discourage this practice for the safety of those involved whilst not also opening a can of worms about human exposure to RF (it was Cold War era and much info was classified)

Hold the phone! You’re telling me now that the government lies to people?!

I have also heard of this tale of “not-spots” but have found no evidence myself. The SWR and near field antennas stuff you mentioned makes a lot of sense, I just didn’t understand how I could be stealing electrons meant for others. I mean, if it worked that way wouldn’t trees also creat not spots, especially if they get to a certain height?! Anyway, thanks for the info, and… 73?