CRS 40 V2
Installation, operation and service manual
M2019/02a
4. S
PREADING
OF
RADIO
WAVES
Central reading system 40 CRS works with wireless data transmission using radio waves. For proper
installation and operation of the system it is helpful to learn at least the basics of radio wave spreading.
4.1. P
ROPAGATION
OF
ELECTROMAGNETIC
FIELDS
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves of the electromagnetic field,
propagating (radiating) through space The speed of these waves in the air is close the speed of light.
Characteristic quantity is wavelength, which is approx. 35 cm at 868 MHz frequency.
Wave can band around obstacles in its way only when its wavelength is much bigger that the size of the
obstacle. Reflection and refraction happens Reflection and refraction of waves occurs at the interface
between two dielectric permittivity different environments. Part of the waves reflects, part breaks. The angle
of reflection equals to the angle of incidence. The reflection occurs even on perfectly conductive surface
(metal) because the electromagnetic radiation does not propagates in it.
In the structure of the apartment house there is a large quantity of various obstacles that have negative effect
on propagation of electromagnetic waves. It is especially any metals (arming, elevator shafts, railings, metal
foils etc.) through which the electromagnetic waves do not pass, only reflects. Also, the construction of
buldings (walls, ceilings) significantly dampens the electromagnetic waves. Therefore the propagation of the
electromagnetic walls in such buildings is rather complicated and is individual for each building.
4.2. P
OSSIBLE
OBSTACLES
TO
PROPAGATION
OF
THE
ELECTROMAGNETIC
WAVES
IN
THE
APARTMENT
BUILDING
The number and placement of the repeater units must be adjusted individually for each object. Most common
obstacles are the following:
•
Wired elevator shafts
•
Metal sheets
•
Metallic layer on windows
•
Aluminum blinds
•
Metal furnishing
•
Large parts of furniture
•
Shielding caused by electrical appliances (TV, audio, washing machine, dishwasher …)
•
Equipment working permanently in 868 MHz range (baby monitor, weather station)
•
Radio hobbyist
11 / 57