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Some thoughts on UHF Crystal Radios

Discussion in 'Home Brew' started by vu2nan, Feb 2, 2016.

  1. vu2nan

    vu2nan Active Member

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    Diode capacitance

    Low capacitance diodes are a must for UHF crystal radios.

    It follows that they are to be so wired that the capacitance between their leads is kept to a minimum.

    This does not imply that the leads are to be cut to minimum length. In fact longer leads facilitate antenna-diode impedance matching.

    Antenna-diode impedance matching

    Stub matching is a must for maximizing the signal strength.

    [​IMG]
    Dipole with a single diode

    Long diode leads may be used to form the stub.

    [​IMG]
    Dipole with coil and diode

    A diode length of λ/4 gives a proper match.

    [​IMG]
    Folded dipole

    A circular stub is best for minimum capacitance between the leads.

    [​IMG]
    Dipole with a single diode / circular stub

    73,



    Nandu.
    http://nandusthoughts.blogspot.in/2016/02/some-thoughts-on-uhf-crystal-radios.html
     
    #1 vu2nan, Feb 2, 2016
    Last edited: Feb 2, 2016
  2. vu2nan

    vu2nan Active Member

    Joined:
    Jul 17, 2013
    Messages:
    104
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    39

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