radio waves are energy. they gave me the baseball game for free when i built the crystal radio set from my Radio Shack 150-in-1 kit. no batteries. no power cord. just free radio forever. why did we stop at the crystal radio? what else can we make that runs off radio waves?

ex- perpetual FreePower LED blinker can be used for markers in dark places, monuments (like an eternal flame), tiny wattage flashlight for keyholes, goofy goggles, promotional items.

why are teeny weeny FreePower crystal radios not sold in stores for one dollar (you supply headphones)?

FreePower! We had it! Where did we put it?
-- gnormal, Feb 14 2001

"Diode-Based Energy Source" http://www.escribe....freenrg/m10443.html
With a big honkin' antenna and an earth ground, you can get about 20 microwatts of power. Whee... [egnor, Feb 14 2001, last modified Oct 21 2004]

The Xtal Set Society http://www.midnightscience.com/
[egnor, Feb 14 2001, last modified Oct 21 2004]

Nokia Developed Wireless Power-Harvesting Phones http://mobile.slash...ng-Phones?art_pos=9
Slashdot discussion [xaviergisz, Jun 11 2009]

i dont know if 20 microwatts is a lot or a little, but my radio worked great and the only antenna was a single wire from the kit.
-- gnormal, Feb 14 2001


Basically, there isn't enough power to be interesting.

However, as anyone who has lived close to a radio transmission tower can tell you, the "inverse square law" means you can get a lot more power under some circumstances.
-- egnor, Feb 14 2001


Rmutt recalls a great article in some RF geek magazine. Apparently the Saudis built a soccer stadium right next to a 100 KW AM radio transmitter (used to broadcast the call to prayer to the failthful). Had to rebuild the stadium with insulators between the steel beams because they were arcing great bolts of lightning. Not quite micropower, but what, 5 times more powerful than the FCC limit?
-- rmutt, Feb 16 2001


Why use radio waves for power when there's far more to be had in another part of the electromagnetic spectrum, namely the visible?

Radio communications is practical only because the natural background noise at radio frequencies is so low. Direct sunlight gives you 100 milliwatts per square centimeter, while a digital cell phone might put out only a few milliwatts and yet still work in the daytime.
-- karn, May 13 2002


How would the energy density look in the 50-60 Hz range? Would it be worth it?
-- walkerj, Jan 25 2003


A more useful kind of "free" energy source can be found in the Freeplay (www.freeplay.net) or Baygen radios and flashlights. Basically, you wind up a big spring that then drives a motor in reverse, generating power.
-- DonutBoy, Jan 26 2003


The power we get from radio waves is not free, it is provided by the radio transmitter. If you collect all of the power available from a radio station you would create a shadow behind that point so no one else could use it. The station would probably not be happy about that.
-- miasere, Jun 11 2009


I hear radioactive salts could do wonders for wireless power.
-- travbm, Oct 29 2015


[travbm] Please stop trolling.
-- xenzag, Oct 29 2015


Nano wires also work to convert infra red em rays directly into electricity.
-- travbm, Oct 29 2015



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