How Things Work: Radio

Radio uses only a portion of the electromagnetic spectrum, but it allows people to communicate with one another, experience visual and audio entertainment, and even explore outer space.

A radio wave consists of two perpendicular sine waves that are formed by electric and magnetic fields. One of the waves is a changing electric field, while the other wave is a changing magnetic field.

Radio signals are made unique by the frequency of their sine waves, or the number of cycles that oscillate per unit of time. Frequency is often measured in hertz, or cycles per second.

In comparison to the rest of the electromagnetic spectrum, radio waves have low frequencies, usually between one million and one billion hertz. Visible light, on the other hand, has a frequency of one quadrillion hertz.

Within the radio spectrum, different frequencies of radio waves are used for different purposes. FM radio, for instance, detects radio waves with frequencies between 88 and 108 megahertz, while cell phones use radio waves with frequencies between 824 and 849 megahertz.

A radio is a device that transmits and receives electromagnetic waves that fall within the radio spectrum. To send and receive signals, a radio uses a transmitter and receiver, respectively.

The transmitter sends the electromagnetic wave into the air by moving electrical current up and down an antenna. When current fluctuates in an antenna, it creates changing electric and magnetic fields that travel together as a radio wave.

The signal is first sent into the air. Then the transmitter imparts information to a radio wave by modifying various properties of the wave. The process of imparting data to a radio signal is called modulation.

There are three types of modulation: pulse, amplitude, and frequency. Pulse modulation (PM) occurs when a radio signal is turned on and off. This kind of modulation is used to transmit information to radio-controlled clocks in the U.S.

Amplitude modulation (AM), on the other hand, varies the amplitude (maxima and minima) of the sine wave. This type of modulation can be used to transmit a radio host’s voice.

Lastly, frequency modulation (FM) alters the frequency of the sine wave. This type of modulation is often used to transmit music because it delivers minimal static.

The electromagnetic wave is transmitted through the air at the speed of light. When it reaches the receiver’s antenna, the fluctuating electric field moves charges up and down in the receiver’s antenna, and the radio picks up the signal.

After the transmitter sends the modulated sine wave, the receiver picks up the radio signal using an antenna. The tuner picks out the particular signal based on frequency, and it amplifies this frequency for the speakers to output.

While radio waves are commonly associated with car radios and boom boxes, they are also used by televisions, cell phones, and satellites.

Television uses radio waves to transmit visual information. On older televisions, antennas receive radio signals from television stations and then display the image on the screen.

In the case of cable television, however, cable companies receive the radio signals from the television stations and transmit this information via a cable to people’s personal televisions.

Cell phones are also radios. They have built-in antennas that allow people to transmit and receive information when they talk with one another.

In particular, when a person speaks into the phone, that information is transmitted to a cell phone tower as radio waves. The information then travels to the other person through a cell phone network.

In astronomy, radio telescopes are used to detect radio waves that are emitted from objects in space. Planets, for instance, give off radio waves through thermal radiation, as do gases around stars through molecular changes. Radio telescopes help astronomers form images of objects in space based on the radio signals that they emit.
Creating radio signals on Earth, on the other hand, simply requires a battery and conductor.

To create your own radio waves, make sporadic contact between a coin and the terminals of a nine-volt battery. This procedure creates a fluctuating current through the coin and battery.

Depending on the rate of fluctuation, this current may produce changing electric and magnetic fields that constitute radio waves. If you’re close to a radio, you can listen for static through the speakers.