SOMERSET AMATEUR

RADIO CLUB PRESENTS

A HISTORY OF EARLY

RADIO

BEFORE CELL PHONES..

BEFORE TELEPHONES...

THERE WAS CRYSTAL RADIO

A CRYSTAL RADIO IS NAMED FOR IT’S MOST IMPORTANT COMPONENT - A CRYSTAL DETECTOR, USUALLY MADE FROM

A CRYSTALLINE MINERAL, SUCH AS GALENA. THIS COMPONENT IS NOW CALLED A DIODE.

A CRYSTAL RADIO HAS NO POWER SOURCE - LIKE BATTERIES. IT USES ONLY THE POWER OF THE

RECEIVED SIGNAL TO WORK.

A CRYSTAL RADIOS HAVE MANY DIFFERENT DESIGNS.

CRYSTAL RADIOS BECAME POPULAR DURING THE GREAT DEPRESSION, WHEN MONEY WAS SCARCE.

IN WORLD WAR II, SOLDIERS BUILT “FOXHOLE RADIOS.” THEY WERE MADE OUT OF A RAZOR AND

A PENCIL POINT.

CRYSTAL RADIOS WERE ALSO BUILT BY PRISONERS OF WAR IN VIETNAM.

CRYSTAL RADIO KITS ARE STILL MADE TODAY.THERE ARE EVEN CRYSTAL RADIO CLUBS!

HOW DOES A CRYSTAL RADIO WORK?

? ?

AN ANTENNA GATHERS RADIO SIGNALS.

THE INDUCTOR AND CAPACITOR FORM A RESONANT CIRCUIT THAT TUNES THE RADIO TO A STATION.

RADIO SIGNALS POWER THE CRYSTAL DIODE.

THE CRYSTAL DIODE DEMODULATES THE SIGNAL.

(detector)

DEMODULATES MEANS TO TAKE THEORIGINAL INFORMATION (AUDIO) FROM

THE SIGNAL.

THE SIGNAL IS SENT TO THE EARPHONES.

How the parts connect

● Antenna

● Capacitor

● Inductor – coil

● Diode 1N34 –

“the cat whisker”

● Earpiece

● Ground

Does it work? We start with the capacitor

What is a Capacitor?● A capacitor is made of two conductive surfaces

● Separated by a non-conductive material

● Non-conductive materials can be air, plastic, paper and many others

● The value of the capacitance is determined by the surface area of the conductive material AND the

quality of the non-conductive material and the distance between the conductive surfaces

● In a direct current circuit the capacitor “stores” or blocks the current flow

● In an alternating current circuit the current is passed through the capacitor

Building a Capacitor

● Step 1

● Assemble

the parts

Building a Capacitor● Step 2

Building a Capacitor● Step 3

Building a Capacitor● Step 4

Building a Capacitor● Step 5

The Inductor● About 130 turns of enameled copper wire

● Enamel is a high quality insulator

● It looks like bare wire

The “cat whisker” 1N34 diode● See B in the chart

● Current flow from Anode to Cathode

● Anode Cathode

No cats will be injured

No batteries will be needed

Ready to put it together?