Discover What Radio Waves Are and Their Roles In Communication
Last Updated on May 24, 2020 by arkadmin
There is a clear distinction of what radio waves are in the aspect of communication,as we all know the basic building block of radio communications is a radio wave.
Like waves on a pond, a radio wave is a series of repeating peaks and valleys.
The entire pattern of a wave, before it repeats itself, is called a cycle. The wavelength is the distance a wave takes to complete one cycle.
The number of cycles, or times that a wave repeats in a second, is called frequency. Frequency is measured in the unit hertz (Hz), referring to a number of cycles per second. One thousand hertz is referred to as a kilohertz (KHz), 1 million hertz as a megahertz (MHz), and 1 billion hertz as a gigahertz (GHz). The range of the radio spectrum is considered to be 3 kilohertz up to 300 gigahertz.
What Radio Waves Are and What They Can Do
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light.
Radio waves have frequencies as high as 300 gigahertz (GHz) to as low as 30 hertz (Hz).At 300 GHz, the corresponding wavelength is 1 mm, and at 30 Hz is 10,000 km.
Like all other electromagnetic waves, radio waves travel at the speed of light in vacuum. They are generated by electric charges undergoing acceleration, such as time varying electric currents.
Naturally occurring radio waves are emitted by lightning and astronomical objects.
Radio waves are generated artificially by transmitters and received by radio receivers, using antennas.
Radio waves are very widely used in modern technology for fixed and mobile radio communication, broadcasting, radar and radio navigation systems, communications satellites, wireless computer networks and many other applications.
Different frequencies of radio waves have different propagation characteristics in the Earth’s atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.
To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union (ITU), which defines radio waves as “electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide”.
The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses.
What Can Radio Waves Do
Radio waves are more widely used for communication than other electromagnetic waves mainly because of their desirable propagation properties, stemming from their large wavelength.
Radio waves have the ability to pass through the atmosphere, foliage, and most building materials, and by diffraction can bend around obstructions, and unlike other electromagnetic waves they tend to be scattered rather than absorbed by objects larger than their wavelength.
The study of radio propagation, how radio waves move in free space and over the surface of the Earth, is vitally important in the design of practical radio systems.
Radio waves passing through different environments experience reflection, refraction, polarization, diffraction, and absorption.
Different frequencies experience different combinations of these phenomena in the Earth’s atmosphere, making certain radio bands more useful for specific purposes than others.
Practical radio systems mainly use three different techniques of radio propagation to communicate:
- Line of sight: This refers to radio waves that travel in a straight line from the transmitting antenna to the receiving antenna. It does not necessarily require a cleared sight path; at lower frequencies radio waves can pass through buildings, foliage and other obstructions. This is the only method of propagation possible at frequencies above 30 MHz. On the surface of the Earth, line of sight propagation is limited by the visual horizon to about 64 km (40 mi). This is the method used by cell phones, FM, television broadcasting and radar. By using dish antennas to transmit beams of microwaves, point-to-point microwave relay links transmit telephone and television signals over long distances up to the visual horizon. Ground stations can communicate with satellites and spacecraft billions of miles from Earth.
- Indirect propagation: Radio waves can reach points beyond the line-of-sight by diffraction and reflection.Diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall. Radio waves also partially reflect from surfaces such as walls, floors, ceilings, vehicles and the ground. These propagation methods occur in short range radio communication systems such as cell phones, cordless phones, walkie-talkies, and wireless networks. A drawback of this mode is multipath propagation, in which radio waves travel from the transmitting to the receiving antenna via multiple paths. The waves interfere, often causing fading and other reception problems.
- Ground waves: At lower frequencies below 2 MHz, in the medium wave and longwave bands, due to diffraction vertically polarized radio waves can bend over hills and mountains, and propagate beyond the horizon, traveling as surface waves which follow the contour of the Earth. This allows mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, out to hundreds of miles. As the frequency drops, the losses decrease and the achievable range increases. Military very low frequency (VLF) and extremely low frequency (ELF) communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater.
- Skywaves: At medium wave and shortwave wavelengths, radio waves reflect off conductive layers of charged particles (ions) in a part of the atmosphere called the ionosphere. So radio waves directed at an angle into the sky can return to Earth beyond the horizon; this is called “skip” or “skywave” propagation. By using multiple skips communication at intercontinental distances can be achieved. Skywave propagation is variable and dependent on atmospheric conditions; it is most reliable at night and in the winter. Widely used during the first half of the 20th century, due to its unreliability skywave communication has mostly been abandoned. Remaining uses are by military over-the-horizon (OTH) radar systems, by some automated systems, by radio amateurs, and by shortwave broadcasting stations to broadcast to other countries.
In radio communication systems, information is carried across space using radio waves.
At the sending end, the information to be sent, in the form of a time-varying electrical signal, is applied to a radio transmitter.
The information signal can be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing data from a computer.
In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency, called the carrier wave because it serves to “carry” the information through the air.
The information signal is used to modulate the carrier, altering some aspect of it, “piggybacking” the information on the carrier.
The modulated carrier is amplified and applied to an antenna.
The oscillating current pushes the electrons in the antenna back and forth, creating oscillating electric and magnetic fields, which radiate the energy away from the antenna as radio waves.
The radio waves carry the information to the receiver location.
At the receiver, the oscillating electric and magnetic fields of the incoming radio wave push the electrons in the receiving antenna back and forth, creating a tiny oscillating voltage which is a weaker replica of the current in the transmitting antenna.
This voltage is applied to the radio receiver, which extracts the information signal.
The receiver first uses a bandpass filter to separate the desired radio station’s radio signal from all the other radio signals picked up by the antenna, then amplifies the signal so it is stronger, then finally extracts the information-bearing modulation signal in a demodulator.
The recovered signal is sent to a loudspeaker or earphone to produce sound, or a television display screen to produce a visible image, or other devices.
A digital data signal is applied to a computer or microprocessor, which interacts with a human user.
The radio waves from many transmitters pass through the air simultaneously without interfering with each other.
They can be separated in the receiver because each transmitter’s radio waves oscillate at a different rate, in other words each transmitter has a different frequency, measured in kilohertz (kHz), megahertz (MHz) or gigahertz (GHz).
The bandpass filter in the receiver consists of a tuned circuit which acts like a resonator, similarly to a tuning fork.It has a natural resonant frequency at which it oscillates.
The resonant frequency is set equal to the frequency of the desired radio station.
The oscillating radio signal from the desired station causes the tuned circuit to oscillate in sympathy, and it passes the signal on to the rest of the receiver.
Radio signals at other frequencies are blocked by the tuned circuit and not passed on.
- Radio waves are a type of electromagnetic radiation best known for their use in communication technologies such as television, mobile phones, and radios. These devices receive radio waves and convert them into mechanical vibrations in the dynamics to create sound waves.
- The radio frequency spectrum is a relatively small part of the electromagnetic (EM) spectrum. The em spectrum is usually divided into seven regions in descending order of wavelength and increasing energy and frequency
- Radio waves have the longest wavelengths in the EM spectrum, according to NASA, ranging from about 0.04 inches (1 millimeter) to more than 62 miles (100 kilometers). They also have the lowest frequencies, from about 3,000 cycles per second, or 3 kilohertz, up to about 300 billion hertz, or 300 gigahertz.