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| Handy Crystal Radio Antenna |
Related post: Crystal Radio Antennas
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Handy Crystal Radio Antenna
In a ham shack, either half of a 40m inverted ' V ' dipole antenna would come in quite handy as a usable crystal radio antenna element.
However, a suitable loading coil would be required to make it resonant at the desired frequency.
Related post: Crystal Radio Antennas
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Related post: Crystal Radio Antennas
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Crystal Radio Antennas
A medium wave broadcast station antenna system generally comprises a ¼ λ vertical element
and earth.
It would not be wrong to infer that such an antenna would be ideal for a crystal radio.
However, practical reasons necessitate use of a much shorter element, with a suitable loading
coil making it resonant at the desired frequency.
Good results would be obtained with an element not shorter than 60 feet.
Related post: My first Antenna
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and earth.
It would not be wrong to infer that such an antenna would be ideal for a crystal radio.
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| Crystal Radio Antenna Arrangement |
coil making it resonant at the desired frequency.
Good results would be obtained with an element not shorter than 60 feet.
Related post: My first Antenna
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Crystal Radio / Piezo Earpiece Interfacing
Here's how to interface a piezo earpiece with a crystal radio.
Parallel-tuned, series-fed radio:
The earpiece is interfaced through a 33 kΩ shunt resistor. The resistor provides a path for the
detector current. The voltage drop across the resistor drives the earpiece.
Series-tuned, shunt-fed radio:
Parallel-tuned, series-fed radio:
The earpiece is interfaced through a 33 kΩ shunt resistor. The resistor provides a path for the
detector current. The voltage drop across the resistor drives the earpiece.
Series-tuned, shunt-fed radio:
The earpiece is interfaced through a 2.5 mH RF Choke to prevent its capacitance from short-circuiting the detector. The voltage drop across the detector drives the earpiece.
Related post: Makeshift Piezo Earphones
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Related post: Makeshift Piezo Earphones
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Ideal detector for a Shunt-fed Crystal Radio
A Germanium transistor may be configured as a diode, having its forward voltage as low as 0.1 V, by just interconnecting its base and emitter.
It makes for an ideal detector in a shunt-fed crystal radio.
Related post: Crystal Radio Circuits - Alternative Concepts
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| Basic Shunt-fed Crystal Radio |
Related post: Crystal Radio Circuits - Alternative Concepts
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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.
A diode length of λ/4 gives a proper match.
A circular stub is best for minimum capacitance between the leads.
Related post: UHF Crystal Radio
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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.
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| Dipole with a single diode |
Long diode leads may be used to form the stub.
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| Dipole with coil and diode |
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| Folded dipole |
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| Dipole with single-diode circular stub |
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