User's Manual

Chapter Two Installation
Man_455U-D Rev 3.01 Page 23
lengths of cable ( and hence more cable loss) can be tolerated. If more than 20 metres of cable
is required for a marginal path
installation, then a low loss cable such
as 10D-FB, or a higher gain antenna
should be used. Collinear antennas
should be mounted vertically, at least 1
metre away from a wall or mast.
2.2.2 Yagi antennas.
A Yagi antenna provides high gain in
the forward direction, but lower gain in
other directions. This may be used to
compensate for coaxial cable loss for
installations with marginal radio path.
The Yagi gain also acts on the receiver,
so adding Yagi antennas at both ends
of a link provides a double
improvement.
Yagi antennas are directional. That is,
they have positive gain to the front of
the antenna, but negative gain in other
directions. Hence Yagi antennas
should be installed with the central
beam horizontal and must be pointed exactly in the direction of transmission to benefit from
the gain of the antenna. The Yagi antennas may be installed with the elements in a vertical
plane (vertically polarized) or in a horizontal plane (horizontally polarized). For a two station
installation, with both modules using Yagi antennas, horizontal polarization is recommended.
If there are more than two stations transmitting to a common station, then the Yagi antennas
should have vertical polarization, and the common (or “central” station should have a
collinear (non-directional) antenna.
Also note that Yagi antennas normally have a drain hole on the folded element - the drain hole
should be located on the bottom of the installed antenna.
2.3 Power Supply
The 455U-D has a 15-28VDC “normal” supply and a 12 - 15VDC alternate supply. The
supply requires a minimum capacity of 24 Watt for the high power radio version (0.5-5W) or
6W for the low radio power version (10 – 500mW).
If the normal 24V supply is used, the 455U will provide battery charging for a 12V sealed
lead-acid backup battery connected to the 12V terminals. The internal battery charger will
provide a float charge voltage of 13.8VDC with current limit set to 1.6A (minimum supply
voltage 15V).
455U-D
Antenna installed
with drain holes
down
Coax feed looped
at connection
90
o