the wonder of a crystal radio set - schedschd.ws/hosted_files/2015albuquerquedukecityhamfest/fe/dchf...
TRANSCRIPT
The Wonder of aCrystal Radio Set
Bill Ripley, KY5Q2015 Duke City Hamfest
Albuquerque, [email protected]
www.stemtrajectory.com
What is a Crystal Radio
• Crystal Radio Receiver
– AKA “Crystal Set”, “Cat’s Whisker Receiver”, “Foxhole Radio”
– Very simple radio receiver, popular in the early days of radio
– Requires no power source other than energy received from the radio signal captured by its antenna
– It gets its name from its most important component, known as a crystal detector, originally made from a piece of crystalline mineral usually Galena, a natural form of Lead Sulfide
– This component is now called a “diode”.
The Simplest Receiver
• Can be made with a few inexpensive parts
– Wire for an antenna
– Coil of copper wire for adjustment (tuning)
– Capacitor
– Crystal detector
– Earphones
Why is a Crystal Set Different ?
• A Crystal set is a passive receiver
– Other radios use a separate source of electric power such as a battery or the mains power to amplify the weak radio signal so as to make it louder.
• Crystal sets produce a rather weak sound and must be listened to with sensitive earphones
• Can only receive stations within close range
Essential Components
• Antenna to capture radio waves
• Tuned Circuit to select particular frequency
– Inductor (coil of wire) & Capacitor
– Resonates at the radio station’s frequency
• Detector
– Extracts audio signal from radio wave
– Rectifies AC radio wave to Pulsing DC current that varies with audio signal
• Earphone
How Do I Get a Crystal Radio ?
• Procure a kit from multiple sources
• Procure the parts and build one yourself
– Use readily available modern components
– Use improvised components like the radio pioneers
• Build a modern variant and substitute many kinds of primitive or home-made components
Commercial Kits
Build Your Own
Crystal Radio Society Kit
Capacitor Crystal Diode
Earphone
Inductor (Coil)
Fahnstock Clips
Cat’s Whisker Detector
Step back in time with a galena
detector kit and experience the
soft detection that comes from
minerals.
Delight in the first broadcast
reception using the galena as a
replacement for those 1N34
diodes
Wood base, mounted galena,
phosphor-bronze cat whisker, 3-
inch brass rod, compression
spring, and brass parts.
Galena Crystal
Galena Crystal Positioning Arm
Foxhole Radio Pictorial Schematic
Foxhole Radio #2Graphite
Contact to
Razor Blade
Razor Blade
Diode
DetectorCoil
Inductor
Variable
Capacitor
For Tuning
Foxhole Radio #3
Lead Pencil
Contact to
Razor Blade
Razor Blade
Diode
Detector
Foxhole Radio #4 Wiper Arm for
Variable Inductor
Toilet Paper
Tube Coil
(Inductor)
Razor Blade
“Detector”
(Diode)
Thank Youwww.STEMtrajectory.com
Bill Ripley, KY5Q2015 Duke City Hamfest
Albuquerque, [email protected]
www.stemtrajectory.com