Electromagnetic waves
The radio waves used in Moeller radio systems are also electromagnetic waves. Other types of electromagnetic waves include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. The difference between these different waves lies in their frequency and their wavelength. Radio waves are waves with a frequency of between 10 kHz (kilohertz) and 300 GHz (gigahertz). They are followed by the higher frequencies of heat or infrared radiation, visible light and X-rays. From a physics perspective, electromagnetic waves are oscillations of the electromagnetic field which disperse in a spherical pattern.
The following equation defines the relationship between frequency (f) and wavelength (?): c = frequency (f) x wavelength (?) or inversely: f ? = c whereby c is the constant speed of light, approx. 300,000 km per second.
The wavelength of the frequency of 868.3 MHz used by Moeller radio systems is therefore 34.5 cm. One advantage of higher frequencies is that signals can be transmitted over longer distances and with less energy. However, it is also a fact that the energy of the waves decreases significantly the further they are from the transmitter – just as the sound of a car's engine fades as it drives away from you. This reduction in energy is inversely proportional to the square of the distance. This means that at just a very short distance from the transmitter, only a fraction of the transmitted energy is received. This in turn means that the receiver has to be very sensitive in order to pick up this weak signal. There are other reasons why it is not easy for radio waves to spread. They can be weakened, deflected, turned around or extinguished. But sometimes they are also amplified. The scientific expressions for these phenomena are absorption, reflexion, polarisation and interference.
Absorption
occurs as radio waves pass through objects. While some waves (light, ultraviolet and infrared radiation) are unable to penetrate solid matter such as walls, furniture and other objects, radio waves can. However, they lose some of their energy as a result of absorption in the process. How much of their energy is lost depends on the thickness, the consistency and the density of the object. High moisture levels in the material also lead to a higher energy fall-off.
Reflexion
is triggered when radio waves hit metallic objects and surfaces (construction steel, door frames and metal doors, metal foil in heat insulation, vapour-deposited metal layers in heat-absorbing glass or metal cabinets). The waves are reflected - like light hitting a mirror. Behind these objects, there is a radio pocket; in front of them the 12 Studybook intensity of the waves can be amplified. However, equipment located in the radio pocket will often still be operational, as it receives reflected radio signals.
Sometimes it can be desirable to keep an area completely free of radio waves. This is done by erecting shielding surrounding the area (Faraday cage, usually made of metal). It is then impossible to trigger devices inside the cage from the outside via a radio system.
Polarisation
is the oscillation on one plane. The transmitter antenna transmits the radio waves with a specific oscillation plane. The receiver antenna also has a preferred oscillation plane. If the two are roughly equal, there is ideal sensitivity for receiving signals.
However, (metallic) surfaces do not only reflect radio waves; they also change their oscillation plane. In a worst-case scenario – if the oscillation plane is turned 90° – the antenna will no longer receive a signal.
Interference occurs when reflected and direct waves overlap. When this happens, there may be areas where the radio waves cancel each other out
Interference
occurs when reflected and direct waves overlap. When this happens, there may be areas where the radio waves cancel each other out.
Modulation
makes it possible to transmit information in the first place. Even if the radio waves reach the receiver successfully, you haven't really achieved much yet. Just as our 50 Hz AC current produces Moeller Building Automation 13 a steady buzzing sound, the radio waves would only generate a steady high tone – if our ears were sensitive enough to hear it, that is. To achieve anything productive, we first have to transmit the information on the radio waves just as music is transferred on sound waves in the form of different notes or rhythms.
Modulation means that either the frequency of the radio signal (frequency modulation) or its amplitude (amplitude modulation) is altered in the rhythm of the data to be transmitted.
There are several variants of each of these two methods for specific applications. The simplest variant is simply to switch the radio signal on and off in a certain rhythm in amplitude modulation.
The radio receiver now has to fulfil several criteria. It has to be able to process received signals of greatly varying strengths: The stronger signal close to the transmitter must not be allowed to cause overmodulation and distortion. At a greater distance from the transmitter, the sensitivity must be high enough to allow evaluation of the very weak signal. The transmitted information must then be read out of the signal received.
