Inter-Organizational Value Chain

RADIOWAVES:-

Radio is the wireless transmission of signals through free space by electromagnetic radiation with frequency significantly below that of visible light, in the radio frequency range, from about 30 KHz to 300 GHz. These waves are called radio waves. Electromagnetic radiation travels by means of oscillating electromagnetic field that passes through the air and the vacuum of space. Transducing information such as sound into an electronic signal, this is then sent as an electromagnetic radio wave from a transmitter. A receiver intercepts the radio wave and extracts the information-bearing electronic signal, which is converted back using another transducer such as a speaker. Information, for example sound, is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude, frequency phase or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form.

Radio Propagation

Electromagnetic waves travel through space either directly, or have their path altered by Reflection, refraction or diffraction. The intensity of the waves diminishes due to geometric dispersion (the inverse-square law); some energy may also be absorbed by the intervening medium in some cases. Noise will generally alter the desired signal; this electromagnetic interference comes from natural sources, as well as from artificial sources such as other transmitters and accidental radiators. Noise is produced at every step due to the inherent properties of the devices used. If the magnitude of the noise is large enough, the desired signal will no longer be discernible; this is the fundamental limit to the range of radio communications.

Application of radio:-

Early uses of radio waves were maritime, for sending telegraphic messages using Morse code between ships and land. One of the most memorable uses of marine telegraphy was during the sinking of the Titanic in 1912.

·         Telephony

Mobiles phones transmit to a local cell site which may be transmitter or receiver that ultimately connects to the public switched telephone network (PSTN) through an optic fiber or microwave radio and other network elements. When the mobile phone nears the edge of the cell site's radio coverage area, the central computer switches the phone to a new cell. Cell phones originally used FM, but now most use various digital modulation schemes. Recent developments in Sweden (such as DROP me) allow for the instant downloading of digital material from a radio broadcast (such as a song) to a mobile phone. Satellite phones use satellites rather than cell towers to communicate.

·       Navigation:-

All satellite navigation systems use satellites with precision clocks. The satellite transmits its position, and the time of the transmission. The receiver listens to four satellites, and can figure its position as being on a line that is tangent to a spherical shell around each satellite, determined by the time-of-flight of the radio signals from the satellite. Radio direction-finding is the oldest form of radio navigation. Before 1960 navigators used movable loop antennas to find the direction. In some cases they used marine radiolocation beacons, which share a range of frequencies. A directional signal rotates like a lighthouse at a fixed rate. When the directional signal is facing north, an Omni directional signal pulses. By measuring the difference in phase of these two signals to establishing a line of position.

·       Radar:-

Radar (Radio Detection and Ranging) detects objects at a distance by bouncing radio waves off them. The direction finding is caused by the echo, which determines the distance. The direction of the beam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide area two to four times per minute. They use very short waves that reflect from earth and stone. They are common on commercial ships and long-distance commercial aircraft.General purpose radars generally use navigational radar frequencies, but modulate and polarize the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms, as well as land and vehicles.

Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. Sometimes search radars use the Doppler effect to separate moving vehicles from clutter. Targeting radars use the same principle as search radar but scan a much smaller area far more often, usually several times a second or more. Weather radars resemble search radars, but use radio waves with circular polarization and a wavelength to reflect from water droplets. Some weather radar use the Doppler Effect to measure wind speeds.

PROPAGATION

·      GROUND WAVE PROPAGATION:-

Radio waves in the very low frequency band propagate in a ground, or surface wave. The wave is confined between the surface of the earth and to the ionosphere. The ground wave can propagate a considerable distance over the earth's surface and in the low frequency and medium frequency portion of the radio spectrum. Ground wave radio propagation is used to provide relatively local radio communications coverage, especially by radio broadcast stations that require to cover a particular locality.Ground wave radio signal propagation is ideal for relatively short distance propagation on these frequencies during the daytime. Sky-wave ionospheric propagation is not possible during the day because of the attenuation of the signals on these frequencies caused by the D region in the ionosphere. In view of this, radio communications stations need to rely on the ground-wave propagation to achieve their coverage.A ground wave radio signal is made up from a number of constituents. If the antennas are in the line of sight then there will be a direct wave as well as a reflected signal. As the names suggest the direct signal is one that travels directly between the two antenna and is not affected by the locality. There will also be a reflected signal as the transmission will be reflected by a number of objects including the earth's surface and any hills, or large buildings. That may be present.

·       SKY WAVE PROPAGATION:-

In radio communication, sky wave or skip refers to the propagation of radio waves reflected or refracted back toward the Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, sky wave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is  used in the shortwave frequency bands.As a result of sky wave propagation, a signal from a distant AM broadcasting station, a shortwave station, or—during sporadic E propagation conditions principally during the summer months in both hemispheres—a low frequency television station can sometimes be received as clearly as local stations.Sky wave propagation is distinct from ground wave propagation, where radio waves travel near Earth's surface without being reflected or refracted by the atmosphere—the dominant propagation mode at lower frequencies, and line-of-sight propagation, in which radio waves travel in a straight line, the dominant mode at higher frequencies. Most long-distance shortwave (high frequency) radio communication—between 3 and 30 MHz—is a result of sky wave propagation.

·       LINE-OF-SIGHT PROPAGATION:-

Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. These transmission includes light emissions traveling in a straight line. The rays or waves may be diffracted, refracted, reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles. At low frequencies below approximately 2 MHz radio signals travel as ground waves, which follow the Earth's curvature due to diffraction with the layers of atmosphere. This enables AM radio signals in low-noise environments to be received well after the transmitting antenna has dropped below the horizon.

Additionally, frequencies between approximately 1 and 30 MHz can be reflected by the Layer, thus giving radio transmissions in this range a potentially global reach, again along multiple deflected straight lines. However, at higher frequencies and in lower levels of the atmosphere, neither of these effects are significant. Thus any obstruction between the transmitting antenna and the receiving antenna will block the signal, just like the light that the eye may sense. Therefore, since the ability to visually see a transmitting ante roughly corresponds to the ability to receive a radio signal from it, the propagation characteristic of high-frequency radio is called "line-of-sight". The farthest possible point of propagation is referred to as the "radio horizon".In practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal (a function of both the transmitter and the antenna characteristics). Broadcast FM radio, at comparatively low frequencies of around 100 MHz, is less affected by the presence of buildings and forests.