Rectifier

Discussion in 'The Projects Forum' started by KCHARROIS, Jul 25, 2012.

  1. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Hello everybody,

    Is it possible to rectify a wireless signal to DC? Would a bridge rectifier consisting of shotkey diodes and then using caps work?

    Thanks
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    The magnitude of a typical WiFi signal is orders of magnitude smaller than the forward voltage drop of a Schottky diode. If look at the power levels of RF signals you can receive, the noise floor is about -135 dBm. The signals a couple of dBm higher. So that is 13 orders of magnitude smaller than a milliwatt. So it's like nanovolts and femtoamps. It is hard to imagine being able to produce useable DC power from a wireless signal
     
  3. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
    1
    But if the signal were to be amplified first wouldnt you be able too?
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    Isn't that how AM radios work????
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    So doesn't it take DC power to build an amplifier to feed the rectifier to feed the cap to what purpose. The process results in a net loss of power. Why would you do that?
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    No. The purpose of an AM receiver is not to produce DC power. The purpose of an AM receiver is to convert the RF energy into AF energy that can be converted to mechanical energy by driving the speaker cone.
     
  7. #12

    Expert

    Nov 30, 2010
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    Umm...I believe the question was about using a rectifier to turn AM broadcast energy into something amplifiable. The same idea crossed my mind. Tuned circuit > rectifier > something changed about the voltage. It's still not a power supply but it seems to indicate that broadcast level energy can be rectified.
     
  8. bertus

    Administrator

    Apr 5, 2008
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    KCHARROIS and #12 like this.
  9. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
    1
    Thanks for the replies, bertus the field strentgh idea will work great thanks again.
     
  10. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
    1
    Another concern of mine is how strong are wireless signals when received. Say I have a transmitter sending a signal of about 50 mW how much power will I receive at the receiver end thats about 10 meters away? The antenna will simply be a copper wire.
     
  11. Papabravo

    Expert

    Feb 24, 2006
    10,138
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    For short wavelength signals used in WiFi, those distances are many wavelengths so you are out of the near field. In the far field the signal strength falls off as 1 over d squared. One way of combating this is to use directional antennas. A piece of wire is pretty far away from being a directional antenna. My guess is that from a 50 mW transmitter you will be dealing with micro volt signals.

    The only way to find out for sure is to run the experiment.
     
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