Nice link Don.
From the article
"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."
Surely with the three pennies, some lemon juice, and a bit of engineuity(!) we could make the battery too!
Many (many) years ago, my friend and I built mini radios using crystals and the smallest 1.5v battery we could get into 'tic-tac' mint boxes. They used deaf aid earphones for the low resistance and tinny sound...
I've just orderd some free samples from Texas Instruments for a new power generation project I'm working on. If all goes to plan, we'll be able to power the radio, and some speakers, with wood, and recharge the cellphone at the same time. :-)