Radio waves. Propagation

Radio transmission system.

A radio transmitter consists of several elements that work together to generate radio waves that contain useful information such as audio, video, or digital data.

- Power supply: provides the necessary electrical power to operate the

transmitter.

- Oscillator: creates alternating current at the frequency on which the

transmitter will transmit. The oscillator usually generates a sine wave, which is referred to as a carrier wave.

- Modulator: adds useful information to the carrier wave. There are two main

ways to add this information. The first, called amplitude modulation or AM, makes slight increases or decreases to the intensity of the carrier wave. The second, called frequency modulation or FM, makes slight increases or decreases to the frequency of the carrier wave.

- Amplifier: amplifies the modulated carrier wave to increase its power. The

more powerful the amplifier, the more powerful the broadcast.

- Antenna: converts the amplified signal to radio waves.

Radio receiver system.

A radio receiver is the opposite of a radio transmitter. It uses an antenna to capture radio waves, processes those waves to extract only those waves that are vibrating at the desired frequency, extracts the audio signals that were added to those waves, amplifies the audio signals, and finally plays them on a speaker.

Antenna: Captures the radio waves. Typically, the antenna is simply a length of wire.

RF amplifier: A sensitive amplifier that amplifies the very weak radio frequency (RF) signal from the antenna so that the signal can be processed by the tuner.

Tuner: A circuit that can extract signals of a particular frequency from a mix of signals of different frequencies.

Detector: Responsible for separating the audio information from the carrier wave.

Of course, there are many variations on this basic radio receiver design. But, these basic elements are found in most receiver circuits.

Radio waves. Propagation.

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths ranging from 1 millimeter to 100 kilometers. Like all other electromagnetic waves, they travel at the speed of light. Naturally, occurring radio waves are made by lightning, or by astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communication satellites, computer networks and innumerable other applications.

The etymology of "radio" or "radiotelegraphy" reveals that it was called "wireless telegraphy", which was shortened to "wireless" in Britain. The prefix radio- in the sense of wireless transmission was first recorded in the word radio conductor, a description provided by the French physicist Edouard Branly in 1897. It is based on the verb to radiate (in Latin "radius" means "spoke of a wheel, beam of light, ray").

Today, the term "radio" specifies the actual type of transceiver device or chip, whereas "wireless" refers to the lack of physical connections; one talks about radio transceivers, but other talks about wireless devices and wireless sensor networks.

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