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free space loss
(FSL)
The radio signal loss occurring as the signal radiates through free space. Free Space Loss = 20 Log
(4(3.1416)d/λ ) where d is in meters. Remembering that λf = c = 300 x 10
6
m/s, the equations reduce
down to:
For the 900 MHz radio band: FSL = 31.5 + 20 Log d (where d is in meters).
For the 2.4 GHz radio band: FSL = 40 + 20 Log d (where d is in meters.)
Frequency
Hopping Spread
Spectrum
(FHSS)
Frequency Hopping Spread Spectrum (FHSS) is a method for generating spread spectrum
transmissions where the signal is switched between different frequency channels in a pseudo-random
sequence known by both the transmitter and the receiver. FHSS is useful for sending small packets of
data in a high interference environment.
902 MHz
928 MHz
1
2
3
25 26 27
. . . . . . . . . . . . . . . . . . . .
Frequency
Power
Fresnel zone
Fresnel zones are the three-dimensional elliptical zones of radio signals between the transmitter and
receiver. Because the signal strength is strongest in the first zone and decreases in each successive
zone, obstacles within the first Fresnel zone cause the greatest amount of destructive interference.
1st Fresnel Zone
2nd Fresnel Zone
3rd Fresnel Zone
Tx
Rx
gain
Gain represents how well the antenna focuses the signal power. A 3 dB gain increase doubles the
effective transmitting power while every 6 dB increase doubles the distance the signal travels.
Increasing the gain sacrifices the vertical height of the signal for horizontal distance increases. The
signal is ‘squashed’ down to concentrate the signal strength along the horizontal plane.
gateway
A gateway is a general network device that connects two different networks.
Gateway
A Sure Cross
®
Gateway is the wireless sensor network master device used to control network timing
and schedule communication traffic. Similar to how a gateway device on a wired network acts as a
"portal" between networks, the Sure Cross Gateway acts as the portal between the wireless network
and the central control process. Every wireless I/O sensor network requires one Gateway device. Every
Sure Cross device is a transceiver, meaning it can transmit and receive data.
GatewayPro
The GatewayPro combines the standard Gateway and the DX83 Ethernet Bridge into one device.
ground loop
Ground loops are grounds within a system that are not at the same potential. Ground loops can damage
electrical systems.
ground plane
A ground plane is an electrically conductive plate that acts as a ‘mirror’ for the antenna, effectively
doubling the length of the antenna. When using a 1/4 wave antenna, the ground plane acts to ‘double’
the antenna length to a 1/2 wave antenna.
heartbeat mode
In heartbeat mode, the Nodes send "heartbeat" messages to the Gateway at specific intervals to
indicate the radio link is active. The heartbeat is always initiated by the Node and is used only to verify
radio communications. Using the Nodes to notify the Gateway that the radio link is active instead of
having the Gateway "poll" the Nodes saves energy and increases battery life.
I am here
Sure Cross
®
DXM100-Sx Wireless Modbus Slave
www.bannerengineering.com - Tel: + 1 888 373 6767
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