A crystal radio is nice because it needs no power, and the materials can all be home-made or at least found around the house. But the crystal radio needs a big antenna, and a good ground, and so is not very portable.
To get away with using a much smaller, portable antenna, we will need to amplify the tiny signal it receives. This requires a portable power supply, such as a battery.
Our next toy is a portable radio. It can be powered from a tiny 1.5 volt battery, or from a battery made from copper wire and aluminum foil sitting in a glass of lemonade, a soft drink, or a beer, or by a few small commercial solar cells.
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