signal-to-noise
ratio (SNR)
The signal-to-noise ratio is the ratio of the signal to any background noise or noise generated by the
medium. In radio terms, it a ratio of the transmitted radio signal to the noise generated by any
electromagnetic equipment, in particular the radio receiver. The weaker the radio signal, the more of an
influence noise has on radio performance. Like gain, the signal-to-noise ratio is measured in decibels.
The equations for calculating SNR are:
SNR = 20 × log (Vs/Vn) where Vs is the signal voltage and Vn is the noise voltage;
SNR = 20 × log (As/An) where As is the signal amplitude and An is the noise amplitude; or
SNR = 10 × log (Ps/Pn) where Ps is the signal power and Pn is the noise power.
single-point
ground
All grounds within a system are made to a single ground to avoid creating ground loops.
site survey
Conducting a site survey, also known as a radio signal strength indication (RSSI), analyzes the radio
communications link between the Gateway (or master radio) and any Node (or slave radio) within the
network by analyzing the radio signal strength of received data packets and reporting the number of
missed packets that required a retry.
slave ID
The slave ID is an identifying number used for devices within a Modbus system. When using more than
one Modbus slave, assign each slave a unique ID number.
By default, Gateways are set to Modbus Slave ID 1.
sleep mode
During normal operation, the Sure Cross radio devices enter
sleep mode
after 15 minutes of operation.
The radio continues to function, but the LCD goes blank. To wake the device, press any button.
slow scan mode
(All internal battery models)In slow scan mode, the device enters a deeper sleep mode to conserve
battery power after the device loses its communication link with its parent or master radio. The device
wakes up periodically to search for its parent radio. If a parent or master radio is not found, the device
goes back to sleep for another sleep cycle. If the parent or master radio is detected, the device exits
slow scan mode. To manually exit slow scan mode, press the binding button.
SMA connector
An SMA connector (SubMiniature version A) is a 50 ohm impedance connector used for coaxial RF
connections and developed in the 1960s. An SMA connector is typically used between the radio and the
antenna.
spread
spectrum
Spread spectrum is a technique in which the transmitter sends (or spreads) a signal over a wide range
of frequencies. The receiver then concentrates the frequencies to recover the information. The Sure
Cross radio devices use a version of spread spectrum technology called Frequency Hop Spread
Spectrum.
star networks
A star topology network is a point to multipoint network that places the network master radio in a center
or hub position. Slave radios only transmit messages to the master radio, not to each other. These
network layouts can be very flexible and typically operate relatively quickly. Slave radios acknowledge
receipt of messages transmitted from the master radio.
For more information on Banner's star network products, refer to the Sure Cross Performance DX80
Wireless I/O Network Instruction Manual (p/n
)
switch power
Efficient power management technology enables some
Flex
Power devices to include an internal power
output supply, called switch power (SP), that briefly steps up to power sensors (ideally, 4 to 20 mA loop-
powered sensors). The warmup time denotes how long the sensor must be powered before a reliable
reading can be taken. After the warmup time has passed, the input reads the sensor, then the switched
power shuts off to prolong battery life.
Sure Cross
®
DXM150 and 1500-Bx Wireless Controllers
104
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