I was worried that your short comments would not be interpreted correctly by the OP (who abviously does not have much RF experience yet), and he would run off and do something that would generate harmful interference. I could just see him trying to do non-pulse-shaped pulse modulation, and stepping all over nearby broadcast receivers (even higher frequency ones). I honestly do not know what the power limits would be for spread spectrum transmissions in the broadcast AM band, and if they are different from unintentional radiator limits. But seeing as the OP's original request was to passively light an LED with the fields... Maybe we could just have him use inductive power transfer at 1MHz? Then as you say, the antenna (the coil) would be small enough to have basically zero radiation resistance.
I've just had way too many problems with harmful interference in my work with HAM radio. At first I thought transmitter hunts (
www.thunt.org) were just fun practice. But now I know that they are definite necessities to keep the emergency communication networks operational. Sorry if I came across kind of heavy-handed in my reply. Interference with licensed communication is not fun at all.