Kasa Radio

"Kasa" means umbrella in Japanese. The kasa radio is a crystal radio made from everyday items (e.g. umbrella, tape, paper clip, etc.) found in the home.

The Kasa Radio (A Radio Made from Everday Items) Necessary Materials

Everyday Items

• Umbrella
• Paper or Board Clip
• Tape
• Polyethylene Bag (6cm×25cm)
• Aluminum Foil (25cm×25cm)
• Insulated Electrical Wire 25m

Electronic Parts (Available at Ocean State Electronics (US) )

• Germanium Diode (1N60, 1N34A)
• Crystal Earpiece (piezo-electric earphone)

Summary of Making the Kasa Radio

1. Wind the insulated electrical wire around the outside of the umbrella.
2. Wrap the polyethylene bag around the inside shaft of the umbrella.
3. Wrap the aluminum foil around the polyethylene.
4. Connect the wires from each section.
5. Secure the wires with the board clip and umbrella catch.
6. Completed !

How to Use the Kasa Radio

The broadcasting frequencies of the radio stations will correspond to the aluminum foil being tightened (e.g. a station with a lower frequency) or loosened (a station with a higher frequency).

Some Interesting Experiments

Replace the Germanium Diode with an LED

It is known that if you forward-bias an LED, it can be used as the rectifier in place of the germanium diode.

However, if you expose an ultra bright LED, such as OptoSupply OSHR3131P, to sunlight, it can be used as the rectifier without a battery.

The exposed LED generates an electric current by a photovoltaic effect.

LED is self-biased by the current and capacitance of a piezo-earphone.

Here is an improved circuit of sunlight exposed LED radio.

Heated silicon diode rectifier

Also, a heated Si diode (e.g. 1N4148, 1S2076A, etc.) can be used as the rectifier.

The V-I (voltage-current) curve for the diode is shifted to the left by an increase in temperature.

At a high temperature, the curves for the Si diodes are approximate to those of room temperature Ge diodes.