Making Things Talk

184 MAKING THINGS TALK

How Radio Works

Radio relies on the electrical property called induction. Any

time you vary the electrical current in a wire, you generate

a corresponding magnetic field that emanates from the

wire. This changing magnetic field induces an electrical

current in any other wires in the field. The frequency of the

magnetic field is the same as the frequency of the current

in the original wire. This means that if you want to send a

signal without a wire, you can generate a changing current

in one wire at a given frequency and attach a circuit to the

second wire to detect current changes at that frequency.

That’s how radio works.

The distance that you can transmit a radio signal depends

on the signal strength, the sensitivity of the receiver, the

nature of the antennas, and any obstacles that block the

signal. The stronger the original current and the more

sensitive the receiver, the farther apart the sender and

receiver can be. The two wires act as antennas. Any

conductor can be an antenna, but some work better than

others. The length and shape of the antenna and the

frequency of the signal all affect transmission. Antenna

design is a whole field of study on its own, so I can’t do it

justice here, but a rough rule of thumb for a straight wire

antenna is as follows:

Antenna length

5,616 in. / frequency in MHz

Antenna length

14,266.06 cm. / frequency MHz

For more information, ...