Bottle Radio

Step #1: Winding the coil.

• Unsurprisingly, the first thing we'll need is a bottle. I'm using a brown glass bottle. Remove the label and rinse it clean.
• Next, we need one of our three spools of magnet wire. Here we'll be using the red 30-gauge wire.
• When winding a coil, it's intuitive to wind "hand over bottle," but this introduces a twist in the wire, something we don't want. A better way to wind a twist-less coil is to put the spool of wire on some kind of spindle and rotate the bottle slowly. Start by sticking down the free end with tape (start at the bottom of the bottle, leaving around 6" of lead wire for connecting later).
• Be careful of the wire. You don't want it to "cross over" itself while winding. Try to keep a constant tension and apply tape as needed to save your position as you wind. You want to make the coils as smooth and closely packed as possible.
• Once complete (using the whole spool) you should have something that looks like image 2 (leave about 8-10" of lead wire at the top, for connecting later). Next we will sandpaper the wire, but before that, apply fast drying sprayable lacquer or shellac (if available) to hold the wire in position. If you don't, you risk loosening the wire when you sandpaper the wire. The lacquer will hold it all together. Also, don't use too much, otherwise you risk waiting over an hour for it to dry.
• The last step is to take a small piece of 150 grit sandpaper, and carefully sand off the red coating in a vertical line (image 3), then gently sand the ends of the wire to expose the copper.