Harvesting available RF makes sense, but using transmitters does not. Besides the signal interference that a transmitter would cause, it is incredibly inefficient and wasteful.

Even so, RFIDs are an exception where the inefficiency is worth the savings in the receiver.

and the law be damned.

With enough (admittedly controversial) evidence to indicate that RF radiation at sufficiently high local energy levels is harmful to people, I say it is a fair trade. No body is paying me to use my airspace as a medium for their transmissions, so if I can tap off some of that trespassing energy to do useful (to me) work,. so much the better.
But note that I don’t think this will ever be useful for any practical purpose beyond small gadgets (unless you happen to live across the street from Radio Berlin).
Also note that energy can also be harvested from high voltage transmission lines in the same way. My grandfather ran the electric fence chargers on his farm from a 300 foot long strand of wire runnning parallel to the high line for decades this way. No doubt at all that this was costing the electric company something since in this case what we had was a physically large single turn transformer subject to the usual transformer energy transform formulae.

@T.

Was the radio station transmitter amplifier on some sort of feedback loop for power output? This seems counter intuitive that the clotheslines would “suck” the power out. Someone turned up the amp not knowing that there was a power sink. Measuring the power output of the transmission at some range using a theoretical efficiency number.

@ A.

Given the dispersion of radio waves you aren’t going to “attract them” with a harvester, only absorb the ones headed in your direction and potentially cause dead spots behind you as they are absorbed, so the closer you are to the transmitter, the greater the arc of your dead spot. Where is this illegal?

In this case, at least, no free lunch.

A little bit of nice history: when Radio Berlin was first set up in last century’s 20′s, gardeners in nearby garden plots found that their metallic clothesline (yes that was when plastics were not very widespread) were carrying measureable voltages. It sufficed to connect a bulb between the line and ground (literally) to light their evening beer and barbecue. Nice early example of energy harvesting?
Not nice for all: the downside was that the radio station had to exchange their power tubes much more often than anticipated. The power for the lighting was literally sucked out of the transmitter which got overloaded. That’s why this early and practical way of energy harvesting got forbidden ever since. Wonder what happens if you place energy suckers near enough to other types of transmitters? Will these transmitters go bust as well? Will the drain of power be noticed and the transmitter cranks up the power to compensate – which completely disrupts the idea of only harvesting energy that is there “anyway” and “for free”.