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Q : HF powered circuit ?

Discussion in 'Electronic Design' started by JCR, Aug 14, 2003.

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  1. JCR

    JCR Guest

    Hi all,

    I'm thinking to supply a low-power circuit (say 300 mW)
    without wire nor battery. I suppose it is possible to
    use a HF emitter with a directionnal beam, to send
    electromagnetic waves to a receiver that will just
    detect and correct the HF to DC.

    Am I dreaming or is reasonable idea ?

  2. Andrew Paule

    Andrew Paule Guest

    Reasonable - many companies have done this
  3. Ian Stirling

    Ian Stirling Guest

    It may or may not be reasonable, and may be hard to do witbout interfering
    with othre stuff.
    How far?
    1mm is almost trivial, 10cm harder, and 10m gets interesting.
    How large/whjat is the object, will it move, ...
  4. Tim Shoppa

    Tim Shoppa Guest

    Define "HF" and "directional beam".

    Transformer coupling power to avoid electrical contacts is done all
    the time. There are at least a couple brands of rechargable electric
    toothbrushes which charge up this way. This isn't usually HF, usually
    it's 60Hz, though scaling this up to the low MHz ought to just work.

    Now, what you're talking about with "HF" and "directional beam" makes
    me think "under 30MHz" (traditional upper frequency of HF band)
    and "Yagi" (a well-known directional antenna). That would imply that to get any
    sort of efficiency, at least one of the antennas is dimensionally larger
    than 10 or 20 feet. Am I thinking of the same thing that you're thinking?

    Even then I'd be surprised if you got efficiencies more than a couple of

    Now, change "HF" to "microwaves" and then we're talking action. (And cooking!)

  5. ISTR Nick Tesla accomplished the wireless transmission of power over
    25 miles or so way back in the 1930s!
  6. James Meyer

    James Meyer Guest

    Yes! Stop thinking about this project. As others have pointed out, it
    is impossible to send energy without having some of it "spill over" and not be
    consumed where you want it. In short, you will probably cook the performer to
    death before you get enough energy into your device to do any good.

    Of course, I have seen several performers who would be better off cooked
    to death.

  7. Tim Shoppa

    Tim Shoppa Guest

    There was a very short Arthur C Clarke story where the audience used their
    reflective programs in an outdoor soccer stadium to do exactly that to a
    dishonest referee...

  8. Jim Meyer

    Jim Meyer Guest

    (Tim Shoppa) wrote in message
    That was one of his that stuck in my mind. Hell, *all* of his
    stories stuck in my mind!

    I always wondered how each audience member got enough feedback to
    be able to place their little spot of reflected sunlight right on the
    ref along with all the other little spots. Then I found out about the
    survival signaling mirror that downed WWII pilots used to catch the
    attention of search planes. Ducedly clever, that.

    Rather than spoil it, I'll let the audience try to come up with
    the method used.

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