In Radio Communications, How Are Signals Transmitted and Received?
To conduct radio communication, first of all, radio waves are emitted. In a radio wave transmitter, there is an important component called an oscillator, which can generate a high-frequency alternating current. When the high-frequency alternating current flows through the antenna, a high-frequency electromagnetic field is generated in space. Because this electromagnetic field is changing periodically, a new electromagnetic field is generated around... So, radio waves are emitted.
Radio broadcasting conveys sound, and television broadcasting conveys not only sound but also images. The high frequency alternating current generated by the oscillator is used to carry information such as sound and images, also known as the carrier wave. The information to be transmitted is added to the carrier and transmitted, and the information can be transmitted to a distant place. Adding information to the carrier wave changes the carrier wave with the signal, a technique called modulation.
There are many radio stations and TV stations in the world, and they are emitting electromagnetic waves all the time. Therefore, there are many electromagnetic waves around us. When receiving radio broadcasts, you must first select the one you need from the numerous electromagnetic waves. When we turn the knob of the radio to select the station, we are actually selecting the electromagnetic waves we need. This is technically called tuning.
After tuning, the receiver gets a specific high-frequency signal current with information. This high-frequency signal current is not yet the required information itself. To get the required sound and image information, they must be "taken" out of the high-frequency signal current. This process is called demodulation. The signal obtained by demodulation is usually amplified. If the sound information is transmitted, the speaker can be made to emit sound; if the image information is transmitted, the display can be made to display the image.
