Some thoughts on UHF Crystal Radios

Discussion in 'Wireless & RF Design' started by vu2nan, Feb 2, 2016.

  1. vu2nan

    Thread Starter Member

    Sep 11, 2014
    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.

    Dipole with a single diode

    Long diode leads may be used to form the stub.

    Dipole with coil and diode

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

    Folded dipole

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

    Dipole with a single diode / circular stub


    Last edited by a moderator: Feb 2, 2016
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    a couple of ferite beads or an rf choke in the headphone leads should stop rf leakage through the headphones, and increase output.