Communication and Media Technology – Radio Technology
Wired connections are not always convenient for the transmission of news or other information. Instead, electromagnetic waves are used, traversing the world with an unseen plethora of radio transmissions.
Electromagnetic waves consist of modulating electrical and magnetic fields, sent and received using various kinds of transducers, commonly known as antennas. The frequency of an electromagnetic wave is its number of vibration cycles per second. The unit of frequency is hertz (Hz). Another characteristic of the wave is its wavelength, or the distance between two successive wave peaks.
Waves in the range of millions of hertz (megahertz or MHz), are used for radio broadcasts, among other applications. They may have wavelengths of several yards. Microwaves, in contrast, have frequencies in the billions of hertz (gigahertz or GHz), and wavelengths of only a fraction of an inch. The size and shape of an antenna depends on the wavelength range for which it is de- signed.
Thin metal rods are used to receive typical radio frequencies. For microwaves, on the other hand, parabolic antennas are used. The “bowl” of the antenna concentrates the waves at the parabola’s focal point. There they are picked up by a detector and sent to the receiving device.
Broadcast methods
The use of electromagnetic waves to transmit relies on a principle called modulation: the signal is “imprinted” in some way on a carrier wave. The type of carrier wave used depends on the application; for instance, a VHF (very high frequency) radio station uses a carrier wave in the VHF band. Several types of modulation are used for various radio technologies.
In the simplest case, the strength of the carrier wave varies according to the pattern of the sound signal (amplitude modulation or AM). The receiving device must be tuned to the desired carrier frequency. The waves received are then amplified, and a demodulator separates the variations from the carrier wave, reproducing the voice signal. Another modulation method (frequency modulation or FM) alters the frequency of the carrier wave according to the pattern of the transmitted signal.
Digitization
As with many other fields of electronics and telecommunications, radio technology is increasingly moving toward digitization. Voice and video signals are transformed into data that can be manipulated using computers. These data files are easier to process and manage; for instance, data errors caused by electro-magnetic disturbances can be corrected even after many transformations and transmission over long distances, creating a much clearer signal.
Digitization also allows various types of data and routing information to be combined. Therefore, in digital radio systems, supplemental text information can be transmitted along with the audio signal.
PROPAGATION OF RADIO WAVES
In space, waves spread out in straight lines. On Earth, their movement depends on the wavelength. Longer waves act as “ground waves,” spreading with the help of the Earth’s electrically conductive surface.
Shorter waves expand in all directions; however, they are directed back to the Earth’s surface by the ionized upper atmosphere. Through a zig-zagging process of reflection, they travel around the entire planet.
BASICS
THE ELECTROMAGNETIC spectrum is split into frequency ranges, or bands, which are used for different technological applications.
Various bands are allocated for radio, aircraft communications, satellite tele-vision, and two-way radio links.