Westermo RM-455U-D - Manual (Page 23)

455U-D Radio Modem User Manual
Page 24 © May 2010
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).
Alternately the 455U can be supplied through the “12V” terminals using a 12-15V supply.
For DC supplies, the negative side of the supply is connected to earth (“Earth” terminal). The
supply negative is connected to the module case internally. The positive side of the supply
must not be connected to earth. The DC supply may be a floating supply or negatively
earthed.
The power requirements of the 455U-D units at 12VDC is 110mA (quiescent) and 2A when
transmitting (5 Watt), or 450mA for 500mW.