Radio propagation Information - basic radio wave propagation

Radio propagation

Radio propagation is a term used to explain radio propagation software how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another.

In free space, all electromagnetic waves (radio, X-rays, visual, etc) obey the inverse-square law which states that an electromagnetic wave's strength is proportional to 1/(x²), where x is the distance from the source. Doubling the distance from a transmitter means the strength is reduced to a quarter, and so on.

Radio propagation on Earth is not only affected by the inverse-square model, but by a number of other factors determined by its path from point to point. This path can be a direct line of sight path or an over-the-horizon (see also radio horizon) path aided by reflection from the ionosphere. A variety of phenomena make radio propagation more complex.

Since radio propagation is somewhat unpredictable, such services as emergency locator transmitters, in-flight communication with ocean-crossing aircraft, and some television broadcasting have been moved to satellite transmitters. A satellite link, though expensive, can offer highly predictable and stable coverage of a given area.

Propagation modes

Radio waves at different frequencies propagate in different ways.

**Radio Frequencies and their Primary mode of Propagation**
Radio Band		Frequency	Propagation Via
VLF	Very Low Frequency	3 - 30 kHz	- Guided between the earth and the ionosphere
LF	Low Frequency	30 - 300 kHz	- Guided between the earth and the ionosphere - Ground Waves
MF	Medium Frequency.	300 - 3000 kHz	- Ground wave during the day - E layer ionospheric reflection at night
HF	High Frequency (Short Wave)	3 - 30 MHz	- E layer ionospheric reflection - F layer ionospheric reflection
VHF	Very High Frequency	30 - 300 MHz	- Line-of-sight - Es layer ionospheric radio wave propagation explained reflection
UHF	Ultra High Frequency	300 - 3000 MHz	- Line-of-sight

The Antenna

The beginning and end of a communication vhf radio wave propagation circuit is the antenna. The antenna will provide gain and directivity on both transmit and receive. The take off angle of the antenna is based on the learn radio propagation type of antenna, the height of the antenna above ground, radio propagation space loss and the type of ground below and in front of the radio wave theory propagation antenna. The take off angle will determine the angle of attack on the ionosphere, which will effect if and where the signal will be reflected by mobile radio propagation lecture the ionosphere.

Ground wave Propagation

Ground Waves are radio waves that follow the curvature of the earth. Ground radio propagation forcast waves progress along the surface of the earth and must be vertically propagation of radio waves polarized to prevent anderson radio propagation model short circuiting the radio signal propagation electric field through the conductivity microwave radio propagation and system gain of the ground. Since the ground is not a perfect electrical conductor, ground waves are attenuated radio propagation as they follow the earth’s surface. At low frequencies, ground losses are low and become lower with decreasing the frequency. The VLF LF frequencies are mostly used for military communications, especially with ships and submarines.

Early commercial and professional radio services radio wave propagation indoor relied exclusively on long wave, low frequencies and ground-wave propagation. To prevent interference with these services, amateur and experimental transmitters were restricted to the higher frequencies, felt to be useless since their ground-wave range was limited. On discovery of the other propagation modes possible at medium wave and short wave frequencies, these became much more useful for commercial and military purposes, and amateur experimentation what effects radio wave propagation was then confined only to authorized frequencies in the range.

Line-of-Sight Propagation

Ground plane reflection effects are an important factor in VHF line of sight propagation. The interference between the direct beam line-of-sight and the ground reflected beam often leads to an effective inverse-fourth-power law for ground-plane limited radiation.

Sky-Wave Propagation

Sky-wave propagation is any of the radio wave propagation modes that rely on reflection of radio waves from anderson 2d radio propagation model the ionosphere, which is made up of one or more ionized layers in the upper atmosphere. These layers are directly affected by the sun, and its varying activity (sunspot cycle) determines the utility of these modes. Forecasting of sky-wave modes is of considerable interest to amateur radio operators and commercial marine radio does gravity effect radio wave propagation propagation planning and aircraft communications, and also to short-wave broadcasters.

Tropospheric Scattering

At VHF and higher frequencies, the atmosphere at a height of around 6 miles (10 kilometres) can scatter radio frequency propagation some of the normally line-of-sight beam of radio frequency energy back toward the ground, allowing over-the-horizon communication between basic radio radio propagation control engineering wave fundamental radio propagation theory propagation stations as what is the radio wave propagation theory far as 500 miles (800 km) apart.

A special form of tropo scattering what is radio propagation relies on reflecting radio waves off the intensely ionized regions generated by meteors. While this mode is very short-duration, lesson in microwave radio propagation and system gain often only a couple of seconds per event, it allows remote stations to communicate to a base that may be hundreds of miles (km) away, without the expense and power input required for a satellite link.

Diffraction

Diffraction phenomena by small obstacles are also important at high frequencies. Signals for urban cellular telephony tend to be dominated by ground-plane effects as they travel over the rooftops of the urban environment. They radio signal propagation versus signal frequency then diffract over roof edges into the street, where multipath propagation, absorption and diffraction phenomena dominate.

Absorption

Low frequency radio waves travel easily through brick and stone. As the frequency rises, absorption effects become more important.

In addition, at microwave or higher frequencies, absorption by molecular resonance in the atmosphere is a major factor in radio propagation. For example, in the 58 - 60 GHz band, there is a major absorption peak which makes this band useless for long-distance what is radio wave propagation use. Beyond around 400 GHz, the Earth's atmosphere is effectively opaque to radio waves.

Heavy rain and snow also present major challenges to radio propagation study microwave reception.

References

Larry D. Wolfgang et. al, (ed), The ARRL Handbook for Radio Amateurs, Sixty-Eighth Edition , (1991), ARRL, Newington CT USA ISBN 0872591689