Intermediate
Crystal Radio
Build a passive AM radio receiver that uses an antenna signal, tuned circuit, diode detector, and sensitive earphone.
Safety first, always.
ElectroLab AI teaches theory, low-voltage electronics, and planning concepts. Mains voltage, switchboards, fixed wiring, high-current systems, and legal electrical work must only be performed by licensed electricians where required.
Open Safety CenterBuild target
Explore resonance, detection, antennas, and radio waves without a battery.
Build steps
1.Wind or prepare the tuning coil.
2.Connect the coil and variable capacitor as a tuned circuit.
3.Add the detector diode from the tuned point to the earphone.
4.Connect a long antenna and a good earth or counterpoise.
5.Tune slowly while listening through a high-impedance earpiece.
What you are learning
1.The LC circuit resonates at selected radio frequencies.
2.The diode detects the audio envelope from AM signals.
3.Antenna length and grounding strongly affect signal strength.
Bench tests
1.Check coil continuity.
2.Try tapping the coil at different turn counts.
3.Compare day and night reception.
Fault finding
1.No stations: improve antenna, ground, or diode orientation.
2.Very quiet audio: use a high-impedance earphone or audio transformer.
3.Only one station: improve tuning range or coil spacing.
Upgrades
1.Add a simple audio amplifier after the detector.
2.Build a better variable capacitor mount.
3.Experiment with different coil diameters.
Project safety
Do not use outdoor antennas near power lines or during storms. Keep antennas far from mains wiring.