Parts of a Crystal Radio – Labeled Set and Circuit

All 15 parts on the diagram

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The set 9

Antenna It collects power from passing radio waves. That power is all the set runs on.
Tuning coil Wire wound round a tube. Using more or fewer turns changes the station.
Tap A place to join on partway along the coil. Each tap uses a different number of turns.
Variable capacitor The other way to tune. Turning its knob meshes the plates more or less.
Detector (diode) It picks the sound signal out of the radio wave. Today it is a small diode.
Earphones They turn the weak current from the detector into sound.
Ground wire It joins the set to the earth: a pipe or a stake.
Crystal A piece of mineral, often galena. It gave the crystal radio its name.
Cat's whisker A fine wire resting on the crystal. The listener moved it to find a sensitive spot.

The circuit 6

Antenna symbol It stands for the antenna, joined to the top of the coil.
Coil symbol It stands for the tuning coil. Its other name is an inductor.
Capacitor symbol Two plates face to face. The arrow means it can be adjusted.
Diode symbol It stands for the detector. Current passes one way only, the way the arrowhead points.
Earphone symbol It stands for the earphones, the last part the signal reaches.
Ground symbol It stands for the ground wire, at the bottom of the coil.

How this list was compiled: Every name checked on 2026-10-01, kept only where two independent sources use it. (1) US Bureau of Standards, Circular 120, Construction and Operation of a Simple Homemade Radio Receiving Outfit (1922, public domain), https://archive.org/details/circularofbureau120unse (antenna, ground wire, tuning coil wound on a cardboard tube, taps, crystal detector with a galena crystal and a fine wire resting on a sensitive point, telephone receivers on a head band). (2) Wikipedia, Crystal radio, text only, https://en.wikipedia.org/wiki/Crystal_radio (no power but the radio wave, wire antenna, ground wire to a pipe or stake, tuning coil, taps, variable capacitor, cat whisker detector, germanium diode, earphones). (3) Simon Quellen Field, Building a crystal radio out of household items, https://sci-toys.com/scitoys/scitoys/radio/homemade_radio.html (earphone, detector, germanium diode, coil with taps, variable capacitor, antenna, ground, and what each symbol of the circuit looks like). (4) For the name cat's whisker also the Computer History Museum, https://www.computerhistory.org/siliconengine/semiconductor-point-contact-rectifier-effect-is-discovered/ (the fine metallic probe on the crystal surface). Licence: own work

The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work

How it works

A crystal radio has no battery and no plug. Tap any ring to see what the part is called, or press Quiz me. The second view shows the same set as a circuit diagram.

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Follow the signal

The antenna, a long wire strung up high, collects a little power from passing radio waves. Its wire comes down to a tap on the tuning coil, which is wire wound round a tube. Picking a tap, or turning the variable capacitor, tunes the set to one station. The detector picks the sound signal out of the radio wave, and the earphones turn it into sound. The ground wire joins the other end of the coil to the earth.

The crystal and the cat's whisker

The detector in the drawing is a diode. The dotted circle shows what it replaced: a crystal of a mineral such as galena and a fine wire called a cat's whisker resting on it.

The quiz also accepts aerial for antenna, headphones for earphones and inductor for coil.

Questions and answers

What are the main parts of a crystal radio?

An antenna, a ground wire, a tuning coil, a detector and earphones. Many sets add a variable capacitor for tuning. Old sets used a crystal and a cat's whisker as the detector; newer ones use a diode.

Why does a crystal radio need no battery?

It runs on the power of the radio wave the antenna receives and has no amplifier. That is why the sound is faint and is heard through sensitive earphones.

Why is it called a crystal radio?

It is named for its crystal detector, which was first made from a bit of crystalline mineral such as galena. That part is now called a diode.

What does the cat's whisker do?

It is the fine wire that touches the crystal. The two together make the detector. The listener moved the wire over the crystal until it rested on a sensitive spot.