Churchill Nano Link IP67, Техническое руководство, Страница: 20 / 42

Page 18
4. Installation
4.1 Mechanical
Data_Link 2000
outstations and base-stations are usually supplied in either steel or polycarbonate enclosures that can
be attached to a wall using conventional fixings. The smaller polycarbonate enclosures provide a high degree of
protection against water ingress, and care is needed to ensure this isn’t compromised by the method of installation.
Most enclosures include cable glands, which are supplied with blanking plugs to maintain a seal. The sealing plugs
must be removed before feeding cables through the glands, and the glands should be tightened around the cables to
maintain the seal. Blanking plugs should be left in any unused glands.
4.2 Aerials
The four types of aerial commonly used on
Data_Link 2000
are whips, end-
fed dipoles, folded dipoles and yagis. Whips and end-fed dipoles are omni-
directional (radiate equally in all directions), so their orientation is not
important. Whip aerials are usually attached directly to
Nano_Link
or
Micro_Link
, or to the top of the enclosure in which they are mounted.
ENF450 end-fed dipole aerials fit into the top of a 2” (OD) pole mounted
externally. CDF450 centre-fed dipoles are useful for mounting on the side
of a pole when the top is not available for an ENF450. Although they
radiate in all directions, the signal is slightly stronger in the direction in
which the balun is pointing (i.e. out of the page, towards the reader, in the
illustration shown).
Yagis are similar to end-fed dipoles, but with reflectors which focus the
signal in the direction in which they are pointing (i.e. to the left in the
illustration shown). This results in signal gain in one direction, at the
expense of loss in all other directions. The directivity and hence gain is
related to the number of elements. A typical yagi, the UHF8, has 8 elements and a gain of
10dB.
Note that approval regulations limit the maximum effective radiated power (ERP) that can
be emitted from a transmitter. If a yagi is used the transmitter output power should be
reduced to compensate for the aerial gain. The aerial gain, however, effectively increases
the sensitivity of the receiver, hence increasing the permissible path loss. Since
Data_Link 2000
uses two-way radio communication, there will be no operational benefit
in fitting a yagi at one end and an omni-directional aerial at the other, since this would
only improve transmission in one direction.
All aerials should be vertically polarised (i.e. the elements should
be vertical, not horizontal). Yagis and end-fed dipoles also have a
defined top and bottom. They must be installed in the orientation
marked by labels attached to them.
External aerial poles can be fixed to walls using either CS6 or SAB
brackets. CS6 brackets space the pole 6” from the wall. SAB
brackets allow the poles to be spaced further from the wall to clear
soffits and gutters, as well as providing a stronger fixing capable of
supporting longer poles.
UHF8
CDF450
SAB
CS6