Radio waves transmit sound, video and other types of information through the air. If you have a radio with an antenna, you can receive this information and listen to music, sports or talk. The radio has several components that help translate the incoming signal and produce recognizable output. Radios come in many forms other than the typical models used for music. For example, a handheld garage door opener remote control may contain a small transmitter that broadcasts a signal to a radio inside the unit mounted in the garage.
The antenna allows a radio to pick up signals being broadcast into the air around it. The radio's range depends on the size and construction of the antenna. A basic wire antenna will not be able to pick up the same signals as a massive tower antenna. The antenna creates an alternating electrical current and sends it to the radio's diode to begin the conversion process from electricity to audio. The antenna may be contained inside the radio case or externally mounted. External antennas typically consist of a series of overlapping aluminum tubes. You can extend the tubes to increase the radio's reception range. Internal antennas use insulated copper wire and a ferrite core to receive the radio signal.
The diode acts as a switch to block part of the electrical current. The current may only flow in one direction through the diode. The resulting current only includes half of the original signal. Lead crystals or vacuum tubes were used as diodes in early radios. Modern radio diodes are typically made from silicon or selenium.
When you tune the radio to a particular frequency, you are adjusting the coil. A radio is constantly being bombarded with signals from various frequencies. Adjusting the coil blocks out all of the frequencies except the one you want to receive. Older radios used a tuning knob to control the frequency while newer models typically have digital tuners. Remote controls and other radios intended for a single use are permanently fixed on the same frequency and do not include a tuning control.
Amplifiers and Speakers
Once the radio signal is ready for playback, it must be amplified and sent through a speaker to become audible. An amplifier boosts the strength of the signal. The speaker receives the electrical current and converts it to sound waves. These sound waves mimic the pattern of the original signal from the radio station. Radio waves travel so fast that you can hear the output from the speaker at nearly the same moment as the station broadcasts them.
Some radios transmit a signal instead of receiving. Transmission begins with an oscillator that generates an alternating current on a specified frequency. The output from the oscillator is known as a carrier wave or sine wave. A modulator adds more information to the carrier wave through one of two methods. Amplitude modulation increases or decreases the wave's intensity. Frequency modulation changes the wave's frequency to modify the information it contains. The signal is also passed through an amplifier to boost its strength before being transmitted from the radio's antenna.