Senin, 04 Juli 2011

Radio Signal

The radio signal is a form of electromagnetic waves, and because they are the way in which radio signals travel, they have a great influence on it's own RF antenna and RF antenna design.

Electromagnetic waves are the same type as the radiation beam of red light, ultra-violet and infra, differ from those in the wavelength and frequency. Electromagnetic waves have both electric and magnetic components that can not be separated. The plane of this field is at right angles to one another and the direction of wave motion.

The results of the electric field of voltage changes occur in the antenna emits RF signals, and magnetic changes result from the flow. It also found that the electric field lines of force in walking along the same axis as the RF antenna, but spread out as they move away from it. This electric field is measured in terms of potential changes over a certain distance, such as volts per meter, and this is known as the field strength. Similarly, when an RF antenna receives signals cause changes in the magnetic currents, and changing electric field causes changes in voltage on the antenna.

There are a number of properties of the wave. The first is the wavelength. This is the distance between a point on one wave to the identical point on the next. One of the most obvious point to choose is at the top as this can easily be identified even if accepted at any point.

The wavelength of electromagnetic waves

The second property of electromagnetic wave frequency. This is the number of times a particular point on the wave moves up and down within a certain time (usually one second). Unit of frequency is Hertz and is equal to one cycle per second. The unit is named after a German scientist who discovered radio waves. Frequencies used in radio are usually very high. In accordance with the prefixes kilo, Mega and Giga are often seen. 1 kHz is 1000 Hz, 1 MHz is a million Hertz, and 1 GHz is a thousand million Hertz is 1000 MHz. Initially the unit was not given a name and frequency of cycles per second (c / s) used. Some older books may show these units together with their prefixes: kc / s; Mc / s, etc. for higher frequencies.

The third key property is the wave velocity. Radio waves travel at the same speed as light. For most practical purposes the speed is considered to be 300 million meters per second although a more precise value is 299,792,500 meters per second.

Conversion of frequency to wavelength

Although the wavelength is used as a measure for the signal, the frequency used exclusively today. It is very easy to connect the frequency and wavelength as it is linked by the speed of light as shown:

lambda = c / f


where lambda = wavelength in meters
f = frequency in Hertz
c = speed of radio waves (light) is taken as 300 million meters per second for all practical purposes.

Field measurements

It is also interesting to note that in order to close the RF antenna there is also the same as the inductive field in the transformer. This is not part of the electromagnetic waves, but can interfere with measurements close to the antenna. It can also mean that the transmission antenna is more likely to cause a nuisance when they are close to other antennas or cables that may have induced signal into it. To receive antennas they are more vulnerable to disruption if they are close to the house wiring and the like. Fortunately this field inductive falls away pretty quickly and is virtually undetectable at distances beyond about two or three wavelengths of the RF antenna.

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