Some thoughts on UHF Crystal Radios

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 single-diode circular stub
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