antenna power feed

Discussion in 'Electronic Basics' started by nav, Mar 3, 2006.

  1. nav

    nav Guest

    hi all
    i would be thankful for ur help on power coupling issues in antenna (rf
    section )
    i need to design a coil for the frequency concerned (f=1/(2pi sqr
    root(lc)) and feed the power to antenna.
    the problem comes in getting correct inductance coil designing and
    testing its value
    and secondly
    why the point of tapping power for antenna needs to be done at
    particular point on coil (i.e. like, one and half turns from positive
    feed)
    thanking you all.
    nav, Mar 3, 2006
    #1
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  2. nav

    Bob Myers Guest

    "nav" <> wrote in message
    news:...
    > hi all
    > i would be thankful for ur help on power coupling issues in antenna (rf
    > section )
    > i need to design a coil for the frequency concerned (f=1/(2pi sqr
    > root(lc)) and feed the power to antenna.


    A coil for what? Coupling to the antenna? If so, coupling
    WHAT to the antenna. Loading an antenna element?
    Acting as an RF choke in a ground connection? You're
    not exactly giving a lot of context for someone to work with,
    here.

    Bob M.
    Bob Myers, Mar 3, 2006
    #2
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  3. nav

    Andrew Holme Guest

    "nav" <> wrote in message
    news:...
    > hi all
    > i would be thankful for ur help on power coupling issues in antenna (rf
    > section )
    > i need to design a coil for the frequency concerned (f=1/(2pi sqr
    > root(lc)) and feed the power to antenna.
    > the problem comes in getting correct inductance coil designing and
    > testing its value
    > and secondly
    > why the point of tapping power for antenna needs to be done at
    > particular point on coil (i.e. like, one and half turns from positive
    > feed)
    > thanking you all.
    >


    The choice of inductance is often driven by the required Q. This may be
    somewhat arbitrarily chosen e.g. anywhere between Q=5 and Q=10 for a class
    C transistor PA stage.

    A tapped coil is an auto-transformer. The tapping point controls loading.
    If you put the tapping in the middle, the transformation ratio is 4:1.

    The dynamic impedance of the (transformed) antenna load across the whole
    coil, the loaded-Q and the inductance are related:

    Loaded Q = R / wL

    w = omega = 2*pi*f
    Andrew Holme, Mar 3, 2006
    #3
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