3
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L A B E L I T A L Y S R L
- V i a S . A l l e n d e , 5 9 – 4 1 1 2 2 M O D E N A
T E L : 0 5 9 / 3 6 2 9 9 3 F A X : 0 5 9 / 3 7 6 0 5 6
P . I V A 0 2 5 7 8 7 5 0 3 6 2 C a p i t a l e S o c i a l e 3 2 . 5 0 0 E u r o
w e b - w w w . l a b e l i t a l y . c o m e - m a i l - i n f o @ l a b e l i t a l y . c o m
The most important and preferred criteria that must
be followed for the protection of the radio electrical
stations are normally the following:
1) Creation of a valid grounding system for the
whole site, this system must have a low resistance
value of discharge dispersion.
2) Shielding of all the electrical and radio electrical
circuits after the supply transformation.
3) Superposition of opportune voltage limiters in the
connection points between the screened and non-
screened circuits including the isolation of such
circuits.
The antenna tower, the equipment room, but also
the transformation box must be connected to the
same grounding system.
Such system must be designed and built in such way that it guarantees the major and uniform
equipotentiality between the different parts. Moreover, the resistance value of discharge dispersion
must be low enough. As far as material is concerned, one can use both copper or zinc-plated steel
under the form of cords or plaits but copper is more resistant to corrosion. In order to avoid more
risk, one can install some isolation transformers in the supply network. One must pay particular
attention to the dispersor, which is directly connected to the antenna tower which is encharged of
dispersing almost all the lightning current to the ground. The dispersor can be either vertical
(pickets) or horizontal (rings or nets), depending on the resistivity of the terrain.
Finally, it will be necessary to link the metallic
fence to the general grounding system, while the
distance between such fence and the dispersors of
the system shall not exceed 5 meters. One should
remember that in order to have a more efficient
shielding, the screens of the cables and the metallic
sheaths must be grounded at both ends. All the
grounding connections must have a short and
rectilinear path and have multiple interconnections.
To conclude, the lightning stroke generally touches
the antenna tower that carries the radiating
antennas.
In order to avoid serious damages it is necessary that the antennas are situated with large margin,
within the protection cone of the tower. Otherwise it is indispensable to install metallic rods that
pick-up the discharges to the top of the tower connected to it with a good electrical contact.
POLARISATION
The Polarisation is an important factor for RF antennas and radio communications in general. Both
RF antennas and electromagnetic waves are said to have a polarization. For the electromagnetic
wave the polarization is effectively the plane in which the electric wave vibrates. This is important
when looking at antennas because they are sensitive to polarisation and generally only receive or
transmit a signal with a particular polarization. For most antennas it is very easy to determine the
polarization. It is simply in the same plane as the elements of the antenna. So a vertical antenna
(i.e. one with vertical elements) will receive vertically polarised signals best and similarly a
horizontal antenna will receive horizontally polarised signals.
