Page 64
J-Series Data Radio – User Manual
Issue 09-10
ANTENNA INSTALLATION
The selection of antennas and their placement is one of the most
important factors when installing a radio based network.
Antennas are generally mounted to a vertical pole with either
vertical or horizontal polarization as per the license requirement.
Antennas should be mounted as high as practical and away from
metal surfaces which can cause reflections.
Determining the type of antenna is very important and as a typical
generic example, Point to Multipoint (PTMP) systems generally
employ high gain (3, 6, or 9dB gain) omni directional antennas
at the Access Point sites and either omni directional whips (unity
gain) or preferably high gain directional yagi antennas (9 or 14dB
gain) at the remote sites.
YAGI ANTENNAS
Yagi antennas not only provide signal gain and directivity, but also
provides protection from interfering signals which are outside the
beam width of the antenna. Yagi antennas are essential when
communicating over very long distances.
Yagi antennas are polarised and must be mounted either vertically
(elements pointing from the ground to the sky) or horizontally
(elements in parallel with the horizon).
When mounting yagi antennas with vertical polarization, it should
be noted that some antennas have a drain hole in the dipole (loop
section of antenna). The small drain hole on one end of the dipole
must be pointed towards the ground so that water will drain out of
the antenna.
OMNI DIRECTIONAL ANTENNAS
Omni directional antennas provide a radiation pattern of equal
strength through 360
0
in the horizontal plane. This makes them
ideal for Access Point antennas in point to multipoint systems
because they can reach a large populous of remote sites.
Omni directional antennas are also used at remote sites (although
yagi antennas are preferred) and are typically ground independent
whip type antennas. The main reason for using whips at remote
sites is for aesthetics as they are far less obtrusive than a yagi.
Regardless of the type, antennas need to be mounted properly and
in a suitable location as covered below.
ANTENNA PLACEMENT
Antenna placement is of paramount importance and plays a big
part of the antennas and in turn systems performance.
When choosing antenna locations the aim is to find the largest path
of unobstructed space and locate the antennas within that space.
It is important to locate antennas as high as possible and definitely
clear of any moving obstructions.
Where possible it is important to avoid mounting antennas:
1. Against or adjacent to steel structures.
2. In an area which will have constant intermittent obstructions
- people walking past, vehicles driving past etc. That is, mount
antennas well above such moving obstructions.
3. Near any electrical equipment.
4. Near metal beams, structures etc.
5. Inside any metal enclosures, tin sheds / warehouses etc. - Note
meshed wire fences act like a “brick wall” to RF transmissions.
6. Away from guard rails or support beams.
7. Above any pipe work or corrugated iron roofs.
Note: Sometimes installations in such environments are
unavoidable and where this is the case, certain care can be taken
to still ensure a reliable installation.
If tests indicate poor signal strength then the antennas at one
or both ends of the link should be raised, and/or moved clear
of obstructing objects, or if directional antennas are employed
they should be checked for correct directional orientation and
polarization (horizontal or vertical signal orientation).
LED Indicators
LED indicators are documented in Part F - Quick Reference Guide
of this User Manual. However, during the installation process it is
important to check that the LED indicators are operating correctly.
DC POWER
If all the LEDs are off, no DC power is reaching the radio modem or
the fuse is open. Successful power-up is indicated by the “Pwr/Tx”
LED showing a continuous GREEN state for REMOTES or an
alternating Red/Green for Access Points.
When the transmitter is active the “Pwr/Tx” LED turns RED.
Sync/No RX LED Indicator
The
“Sync/NoRx” LED is used to indicate the state of the receiver.
A regular flashing GREEN LED shows that the modem is
synchronised to its Access Point. The GREEN LED also flashes
when the modem is receiving data.
A regular flashing RED indicates the REMOTE not synchronised to
an Access Point or BRIDGE. Check the antenna, RF signal levels
and ensure the SubNet names are correct.
LAN LED Indicator
The Green Link and Amber Activity LEDs indicate Ethernet status
on the two LAN ports. These LEDs will show solid Green when
an Ethernet Link is established and will flash Amber to indicate
Ethernet data transmission is occurring.
Part H – Installation & Commissioning
Содержание JR240
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