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Is it possible to generate a small DC power from Radio waves?If yes then how?

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    \$\begingroup\$ How much power? \$\endgroup\$ Jun 21 '13 at 7:04
  • \$\begingroup\$ I noticed this a while ago that's worth a read about a company that produces RF energy harvesting components: au.mouser.com/applications/rf_energy_harvesting \$\endgroup\$
    – PeterJ
    Jun 21 '13 at 7:07
  • \$\begingroup\$ @LeonHeller I just want to know that is it possible or not?If it is possible then what should i do \$\endgroup\$
    – Atom
    Jun 21 '13 at 7:13
  • \$\begingroup\$ It's possible but it wont yield useful amounts of power. I'm sure this Q has been answered elsewhere (perhaps on physics.SE) \$\endgroup\$ Jun 21 '13 at 7:56
  • \$\begingroup\$ It is possible en.wikipedia.org/wiki/… \$\endgroup\$ Jun 21 '13 at 8:59
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Yes, it is possible. In fact, crystal radios work on this basis. With a reasonable antenna and a powerful enough AM station, they can drive a high impedance headphone to well-audible volume using only the power received by the antenna.

The basic trick is to us a transformer to step up the low RF voltage picked up by the antenna. Antennas tend to be rather low impedance, like 75-300 Ω. The output of the transformer would be at a higher voltage, although also at a higher impedance. The higher voltage is important so that the forward drop of a diode is small compared to the voltage, and therefore doesn't loose too much power when rectified.

In a crystal radio, the secondary of this transformer had a capacitor accross it to form a tuned circuit that resonated at the desired radio station's frequency. This capacitor was adjustable so that different radio stations could be received.

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  • \$\begingroup\$ When I was in the 10..12 years range I made crystal radios for all my friends. I always used a single coil (not a transformer). A good (long) antenna, a good earth, and a high impedance headset were critical. A tuning variable capacitor was not that critical: you could hear a few stations simultaneously anyway :) \$\endgroup\$ Jun 21 '13 at 15:34
  • \$\begingroup\$ I made a crystal radio about a year ago, but it didn't generate DC as far as I know. Here is the circuit. Are you talking about another crystal radio circuit, that does generate DC? Or am I wrong, and does my circuit generate DC? \$\endgroup\$
    – user17592
    Jun 21 '13 at 16:51
  • \$\begingroup\$ @Camil: Note the diode in your schematic. That means the output will be positive. In this case is will have a pulse for each carrier cycle. Bascially it's a half-wave rectifier circuit without the output filter cap. If you add the cap, then you will get a more steady voltage. \$\endgroup\$ Jun 21 '13 at 23:38

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