AvaLAN Wireless AW900R4 - Manual (Page 3)

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User’s Manual AW900R4
Operational summary
The AW900R4 Outdoor Wireless RS-485 Radio is designed for indoor or outdoor use,
packaged in a weatherproof die-cast aluminum enclosure with gasketed cover and
connectors that meets the IP66 Standard for water and dust resistance. It may be
used with all of AvaLAN’s 900 MHz antennas and other accessories such as lightning
arrestors and pole-mount brackets.
RS-485 is a point-to-multipoint serial data bus that requires just three wires: two
differential data lines and a common. Because there is no handshake involved, all
devices on the bus must be configured for the same data protocol and timing or
communication will not occur. Also, it is possible to lose data if a receiving device
cannot keep up with a sending device. The AW900R4 supports data rates from 9600
Baud to 115,200 Baud and has a 4 KB data buffer. A set of AW900R4 modules behave
just like an RS-485 bus but without the length constraint and without a physical
wire. They can be used to wirelessly interconnect individual RS-485 devices and can
also link multiple separate busses.
Configuring a wireless link with the AW900R4 requires the establishment of six
elements:
• One radio must be configured as the Access Point (AP) and all others must be
configured as Subscriber Units (SU). Up to 16 SUs can be linked to one AP.
• All radios must share a common Network Name, a 32-bit identifier.
• All radios must share a common 128-bit encryption key.
• The AP and SUs must agree on which radio frequency channel they are using.
This can be manually set or allowed to change automatically.
• The serial port settings: Baud rate, number of data and stop bits and sense
of Parity bit, must match between each radio and the RS-485 bus wired to it,
although the radio link may have different settings at each end.
• The AP and SUs must share a common set of tuning parameters: Next Byte
Delay, Minimum Packet Size and Maximum Packet Size.
AW900R4 radios are configured with a utility program from AvaLAN by removing the
cover and connecting to a USB port on the module inside. The LED display on the
module is also a very useful indicator of the condition of the wireless connection.
The access point (AP) automatically scans for the best of the 12 available radio fre-
quency channels, encrypts RS-485 data received, and broadcasts it wirelessly to all
linked subscriber units (SUs). The AP is constantly monitoring the radio link and can
automatically change the channel if performance is degraded due to interference.
If two AP units are very close to one another, they may interfere if operating on
adjacent frequency channels. Place them at least 10 feet apart or manually select
non-adjacent channels for their operation. Also, each SU should be placed at least
10 feet from the AP to avoid overloading the radio’s receiver.