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By Liudmila Dolzhenkova

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are made by lightning, or by astronomical objects.

Radio waves travel at the speed of light in a vacuum. When passing through an object, they are slowed according to that object's permeability and permittivity.

Part 1. My personal interpretation

Firstly i would like to answer this question by my own,without using Google and other resources.

Every material consists of atoms. Radio waves are much bigger that those atoms, so in that case they can go through walls, windows and etc, when at the same time light cannot travel through the wall, just because its atoms are smaller.

But that ‘rule’ works not every time. As we know, the main characterizing parameters of radio waves are: frequency, wavelength and shape. Radio waves can pass freely through the air or vacuum (also in space), but at the same time not through conductive materials, for example antenna or metal wire. The radio wave cannot pass through that material but by it creates a portion of energy conductor, the electrical current therein appears (it is working for wireless transmission of various kinds of information at the distance).

As you could understand this is a really wide subject for discussion, I have just written down my personal view.

Part 2. Questions for this subject

2. how the earth affect the data travelling (radio waves)?

1.  Radio waves are a part of the electromagnetic spectrum. They do not require a "medium" to travel through. A radio wave is composed of an electrical wave, and a magnetic wave. The 2 waves travel together, creating each other as the wave travels through what ever medium it is in, be that air, wire, or what we call "space".

Actually, radio waves travel very quickly through space. Radio waves are a kind of electromagnetic radiation, and thus they move at the speed of light. The speed of light is a little less than 300,000 km per second. At that speed, a beam of light could go around the Earth at the equator more than 7 times in a second.

The reason that it takes so long for radio messages to travel in space is that space is mind-bogglingly big. The distances to be traveled are so great that even light or radio waves take a while getting there. It takes around eight minutes for radio waves to travel from the Earth to the Sun, and four years to get from here to the nearest star.

A radio wave can be viewed as its own transport vehicle ("self-sufficient"). Space has no atmosphere (and thus no molecules), so, for example, sound cannot travel. However radio waves aren't dependent on their environment in that way, so they are able to travel in space.

2.  Any signaling system consists of three main parts:

• transmitter

• intermediate - connecting lines.

For radio intermediary is an environment - a space in which radio waves propagate.

For propagation in the natural trails, in an environment where the medium is the earth's surface, the atmosphere, outer space, the environment is the link radio system, which is virtually impossible to control.

For propagation in the environment occur:

• change in the amplitude of the wave field (usually due to a decrease in the scattering and absorption)

• and changing the direction of propagation speed,

• rotation of the plane of polarization (Faraday effect)

• time delay and distortion of the transmitted signals.

In the atmosphere surrounding the Earth, there are three areas that affect the propagation of radio waves:

• troposphere,

• stratosphere

• ionosphere

The boundaries between these regions are not expressed strongly and depend on the season and geographical location.

Troposphere is called the surface layer of the atmosphere, extending up to the tropopause (the transition layer between the troposphere and the stratosphere) lying above the equator at an altitude of 16-18 km in temperate latitudes - 10-12 km in the polar regions - 7-12 km. The height of the tropopause varies depending on the time of year. The troposphere is heterogeneous in both the vertical direction and along the surface. Its electrical parameters change when meteorological conditions.

The stratosphere extends from the tropopause up to altitudes of 50-60 km. Stratosphere differs from the troposphere significantly lower density of air and the law of the temperature distribution in height. Radio Waves stratosphere has the same impact as the troposphere, but it is less pronounced because of the low air density.

The ionosphere is the region of the atmosphere at an altitude of 60-10000 km above the earth's surface. At these altitudes, air density is very low and the air is ionized, t. E. A large number of free electrons (electrons of about 103-106 in 1 cm3 of air). The presence of free electrons greatly affects the electrical properties of the ionosphere, and as a result, the conditions of transmission of EM waves.

In the propagation of electromagnetic wave through the medium dielectric constant or refractive index which varies along the propagation path (and the Earth's atmosphere is just such an environment), changing the direction of propagation (curvature of the trajectory), and decreases the speed of wave propagation. This leads to a range estimation errors when the calculated distance from the radar to the pixel does not correspond to actual electromagnetic wave traveled path. The error range is directly converted into phase estimation error by the wavelength of the carrier signal.

Part 4. Last words...

Strong influence on the propagation of radio waves have obstacles. As a general rule, obstacles have reflective properties. As obstacles can be different objects, both natural and artificial origin. As described earlier, the radio waves reflected from the Earth's surface. It is worth noting that if the soil is strongly dry (eg in the desert), the reflection of radio waves is much worse than when the earth crude from the rain. Thus, the communication distance at the same communications equipment at sea by 50 - 70 percent more than on land. Reflect radio waves trees and clouds. These natural obstacles are good reflectors because their composition is water. To the artificial barriers that reflect radio waves include various metal constructions, including reinforcement of buildings and structures.

## What signal does GPS use

There are currently between 27 and 32 global positions system (GPS) satellites in orbit around the earth. Of these, three act as backups. Each satellite transmits a regular GPS signal that is carried by radio waves in the microwave part of the electromagnetic spectrum.

Each GPS satellite continuously broadcasts a navigation message at 50 bits per second on the microwave carrier frequency of approx 1600 MHz .FM radio, for comparison, is broadcast at between 87.5 and 108.0 MHz and Wi-Fi networks operate at around 5000 MHz and 2400 MHz More precisely, all satellites broadcast at 1575.42 MHz (this is the L1 signal) and 1227.6 MHz (the L2 signal).

The GPS signal gives the precise "time-of-week" according to the satellite's onboard atomic clock, the GPS week number and a health report for the satellite so that it can be discounted if faulty.Each transmission lasts 30 seconds and carries 1500 bits of encrypted data. This small amount of data is encoded with a high-rate pseudo-random (PRN) sequence that is different for each satellite. GPS receivers know the PRN codes for each satellite and so can not only decode the signal but distinguish between different satellites.

References:

http://www.fnal.gov/pub/science/inquiring/questions/mikep.html

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