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How to make simple radios

Transmitters

Receivers

Abstract Circuits

Crystal Radio (AM)

  • A crystal radio is the simplest type of radio receivers

  • They are passive receivers, because they are not amplified with external power

  • How a Crystal Radio works by RimstarOrg on YouTube

    • Crystal vibrates to produce sound
    • Two coils can be used for tuning into a frequency (Selectivity)
    • Diode is used to get only the positive envelope of the AM carrier wave
    • The crystal can only react to the lower audio frequencies, not to the radio frequencies
    • A capacitor (bypass capacitor) is used to smooth out the radio waves
    • The distance between coils may cause energy loss, and this is called sensitivity
    • Bringing the coils closer will cause electromagnetic interference, and this is called coupling

Specific Circuits

Simple (no coil)

Tuned (single coil)

Tuned (two coil)

DIY Receivers

Foxhole Radio (AM)

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