How Do Radios Work?
By: Layne W.

2012



Introduction
Radios were invented in the late 1890’s. An Italian scientist named Guglielmo Marconi got much credit for inventing the radio. In 1987 he developed a company that developed several uses for the radio. Radios are used to listen to music, and for talk shows. The first radio station to broadcast was located in Pittsburgh, Pennsylvania in 1920. Radios are located in cars, houses and at some workplaces.



The Overall Idea of How Radios Work
Radio Picture.jpg
Figure 1. This is a radio. The tall part at the top is the antenna, and the knob on the top is the tuner. The black circle is the speaker. The bottom left button tunes the radio from AM to FM. The plus and minus buttons control the volume. The on off button turns the radio on and off.

The process of sending and receiving radio signals involves two machines, the transmitter and the receiver. The transmitter sends out the radio waves and the receiver receives the waves from the transmitter. First, the transmitter turns the sound, picture, or music into an electric signal, the transmitter combines the signals with radio waves of a certain frequency. Next the waves spread out from the transmitter’s antenna in many different directions. The receiver now picks up the waves with its antenna. The receiver separates the electric signal from the radio wave. The receiver now turns the electric signal back into its original picture or sound. The receiver now picks up the sound (it will only pick up picture if it is a television receiver). It sends the sound to a speaker so it can be heard. Finally, people can listen to the radio.





Transmitting the Signal
A battery and a wire is a basic idea of how radios transmit signals. The battery sends electricity (a stream of electrons) through a wire if you connect the wire between two terminals of the battery. The moving electrons create a magnetic field that surrounds the wire. That field is strong enough to affect a compass. Inside radio antennas the same basic process converts a sine wave from the transmitter into varying electromagnetic waves that a receiver picks up.

Radio Waves.gif
Figure 2. These are different types of radio waves.




Modulation
A sine wave and a transmitter transmitting the sine wave into space with an antenna is a radio station. For sound there must be certain information in the sine wave. You have to modulate the waves in certain ways to encode it with certain information. The four most common ways of modulation are Pulse Modulation (PM), Amplitude Modulation (AM), Frequency Modulation (FM), and XM Satellite radio. In Pulse Modulation you simply turn the sine wave on and off, it is a very easy way to send Morse code. PM is generally not used as much as AM and FM. One PM transmitter can send signals all throughout the U.S.A. AM radio stations use amplitude modulation, which is also what the picture of analog television uses. When using AM the amplitude of the sine wave changes. An example of that would be that the sine wave is produced by a person’s voice is overlaid onto the transmitter’s sine wave to vary its amplitude. Numerous radio stations and other various devices use FM. In FM the transmitter’s sine wave frequency slightly changes based on the information signal. XM radio is a satellite radio service. Satellite radio has been in use in America since 2001. In most cases the information is created and then sent out to two overhead satellites. XM uses two satellites so the information can easily be broadcasted. To receive XM radio you must have a special antenna because these types of antennas pick up specific digital signals, sent out by XM transmitters.



Receiving Signals
If you tune your car’s AM radio station, for example 780,000 AM, the transmitter’s sine wave is transmitting at 780,000 Hz (or cycles per second, where the sine wave repeats 780,000 cycles per second). The radio station’s DJ’s voice is modulated onto a carrier wave by varying the amplitude of the transmitter’s sine wave. An amplifier amplifies the signal to something like 50,000 watts to a large AM station. The antenna sends out the wave into space.

These Are the Steps of Receiving a Signal:

1) To receive, the radio must have an antenna, unless you are sitting right next to the transmitter. The antenna’s job is to pick up the correct waves that the transmitter has sent out.
2) The radio receiver also needs a tuner. As the antenna receives thousands of sine waves the tuner separates the waves from the waves you want to listen to and the ones you don’t want to listen to. In this case the tuner is set to receive the 780,000 Hz signal. Tuners work by using a principal called resonance. The tuners resonate and amplify one frequency, and ignore all the rest.

Research the Topic Diagram.jpg
Figure3. This is a diagram of how radios send and recieve signals.




3) The tuner causes the radio to receive only one sine wave. The radio has to extract the DJ’s voice from the sine wave. The part of the radio that does this is called the detector. In AM radio the detector is made with a diode, this allows the current to flow in one direction only, in other words it clips off one side of the wave.
4) Next, the radio amplifies the signal it has clipped. It sends it to the speakers or headphones. The amplifier is made of one or more transistors, the more transistors means more amplification, and that means more power to the speakers.



Glossary
  • Electromagnetic- Is the interaction of electric and magnetic fields. A radio wave is a type of electromagnetic wave.
  • Electron- The molecules in the electric signal the transmitter sends.
  • Oscillates-To move up and down.
  • Sine Wave- Is the type of wave that several radios use.

Citations
Ardley, Neil. How Things Work. New York, Pleasantville: Reader's Digest, 1995. Print.
Brain, Marshall. More How Stuff Works. New York: Wiley Pub, 2003. Print.
"Radio." Britannica Elementary Encyclopedia. Encyclopædia Britannica Online School Edition.
Encyclopædia Britannica, Inc., 2012. Web. 24 Sept. 2012.
Tech-FAQ. "How XM Radio Works." 2012. Web. 24 Sept. 2012.