The structure of a radio station is simple: all you need is a microphone, soundboard, transmitter, antenna, receiver and a bit of physics knowledge to make everything work. It is in physics that lies the answer to how to make a sound propagate through electromagnetic waves through the air. Many people pursued this idea at the end of the 19th century: whoever could find a way to replace the telegraphs and cables used to send messages would become rich. The Italian Guglielmo Marconi managed to make the sound be transmitted to a receiver without the aid of wires and is considered the inventor of the radio, although others have achieved a similar result, such as the Brazilian Roberto Landell de Moura. Today the technology is not only used to transmit music on more than 7,000 official stations in Brazil, but it is also the basis for the operation of various devices, from cell phones to remote controls.
When leaving the station, sound propagates as a wave until it reaches the radio.
1. The studio of a radio station is acoustically insulated, usually with foam, which blocks the entrance of external noise. There, the announcer speaks into the microphone, which is a “transducer”: it receives the vibration of the voice into mechanical waves and converts them into an electric current.
2. The microphone is connected to a soundboard, as well as the CD or MP3 player and the computer where commercials, sound effects and, of course, music are stored. The function of the soundboard is to unite these sounds to others, such as the listeners’ phone calls, and to sift what is on air.
3. The signal in the form of electrical impulses that comes out of the table is weak, so it passes through an amplifier, which increases the intensity of electric current through an electronic circuit. This amplification can be hundreds or thousands of times, depending on the area affected.
4. At the top of the station is the antenna – there, it is easier to prevent the signal from being interrupted by buildings or geographic accidents. It receives electrical signals and transforms them into electromagnetic waves. Each antenna emits two types of signal together: the carrier wave, which carries the radio frequency, and the amplified current, which contains the sound.
5. These signals reach the receiver, the radio set. When we move the dial, an internal circuit causes the device’s antenna to oscillate according to each station. The loudspeakers then convert the electrical waves into mechanical vibrations, which are the sound itself.
System uses satellites instead of transmitting antennas
In the US, since 2002, fully digital radios have operated. The signal does not come from a transmitting antenna, but from satellites. The radio station XM has two of them: Rock and Roll, 35 thousand kilometers from Earth. The receiving radio has to be prepared to decode the information and show data such as the album and the artist’s style on the screen. But you have to pay a subscription, as with cable TV
What do the numbers on the dial mean
In Brazil, the frequency of FM radio stations starts at 88.1 MHz and goes up to the band of 108 MHz. Each station is separated from the other by at least 200 kHz. On AMs, the dial goes from 520 to 1610 kHz, with 10 kHz steps. Thus, there is a limited number of “spots” for broadcasters. Pirate radios, which do not have government concessions, act by “invading” the frequency of other stations. They manage to do this because, even using bad antennas, they transmit at great power, which makes someone passing close to the transmitter pick up the signal by accident.