Make Electronics

What Next? 263

Experiment 31: One Radio, No Solder, No Power

wire. Use your two thumb nails to pull the insulation apart, revealing about a
half-inch of bare wire, as shown in Figure 5-61. Bend it at the center point and
twist it into a loop, as shown in Figure 5-62.

You just made a “tap,” meaning a point where you will be able to tap into the
coil after you wind it. You’ll need another 11 of these taps, all of them spaced
50 inches apart. (If the diameter of the bottle that you’ll be using as the core
of your coil is not 3 inches, multiply its diameter by 16 to get the approximate
desired spacing of taps.)

After you have made 12 taps, cut the wire and strip 6 inches off that end. Now
bend the end into a U shape about a half-inch in diameter, so that you can
hook it through the pair of holes that you drilled at one end of the bottle. Pull
the wire through, then loop it around again to make a secure anchor point.

Now wind the rest of the wire around the bottle, pulling it tightly so that
the coils stay close together. When you get to the end of the wire, thread it
through the remaining pair of holes to anchor it as shown in Figure 5-63. The
completed coil is shown in Figure 5-64.

Figure 5-62. Each exposed section of wire
is twisted into a loop using sharp-nosed
pliers.

Figure 5-63. The stripped end of the wire

is secured through the holes drilled in the

bottle.

Figure 5-64. The completed coil, wrapped

tightly around the bottle.

Your next step is to set up an antenna. If you live in a house with a yard outside,
this is easy: just open a window, toss out a reel of 16-gauge wire while holding
the free end, then go outside and string up your antenna by using polypro-
pylene rope (“poly rope”) or nylon rope, available from any hardware store,
to hang the wire from any available trees, gutters, or poles. The total length
of the wire should be about 100 feet. Where it comes in through the window,
suspend it on another length of poly rope. The idea is to keep your antenna
wire as far away from the ground or from any grounded objects as possible.

If you live in an apartment where you don’t have access to a yard outside, you
can try stringing your antenna around the room, hanging the wire from more
pieces of poly rope. The antenna should still be about 100 feet long, but obvi-
ously it won’t be in a straight line.

Hook the free end of your antenna to one end of your coil. At this point, you also
need to add a germanium diode, which functions like a silicon-based diode but
is better suited to the tiny voltages and currents that we’ll be dealing with. The
other end of the diode attaches to one of the wires leading to a high-impedance

Figure 5-61. Wire strippers expose the solid

conductor at intervals along a 22-gauge

wire.

High Voltage!

The world around us is full of electric-

ity. Normally we’re unaware of it, but

a thunderstorm is a sudden reminder

that there’s a huge electrical poten-

tial between the ground below and

the clouds above.

If you put up an outdoor antenna,

never use it if there is any chance of a

lightning strike. This can be extreme-

ly dangerous. Disconnect the indoor

end of your antenna, drag it outside,

and push the end of the wire into the

ground to make it safe.