Campbell Scientific NL240 Wireless Network Link Interface - Manual (Page 22)

NL240 Wireless Network Link Interface
RSSI in the NL240 is measured in a scale between –100 dBm and 0 dBm. The
higher the number (i.e. –12 dBm as compared to –72 dBm), the better the
connection between Wi-Fi devices. A reliable connection will be maintained if
the RSSI reading in the NL240 stays between –85 dBm and –15 dBm. A
weak, and thus intermittent, connection will have readings between –85 dBm
and –95 dBm. For every 3 dBm increase, the NL240 is receiving twice as
much signal (radiated power). For every 3 dBm lost, the NL240 is receiving
50% less signal.
To improve your RSSI readings, shorten antenna cable lengths and use
frequency matched antennas with higher gain. An NL240 with a 0 db gain
antenna can achieve ranges of up to 32 meters (120 feet) indoors and 95 meters
(300 feet) outdoors. Ranges can be improved by installing higher gain
antennas on both the NL240 and/or the wireless access point. Remember that
RSSI can also be affected by weather, vegetation, terrain, interference, and
antenna cable length and type.
6.4 Antennas
Antenna selection and placement can greatly affect the strength of the signal
you transmit and receive and therefore can impact the quality of
communications with your device. The NL240 should be paired with an
antenna designed for Wi-Fi communications at 2.4 GHz (2.401 to 2.483 GHz).
Ideally the antenna will be connected directly to the NL240 or positioned in
such a way as to minimize coaxial cable length. Note that coaxial cables
attenuate signals more as frequency increases; care should be taken when
selecting the type and length of coaxial cable used with the NL240. The
NL240 antenna connector is RPSMA male. When connecting directly to the
NL240, select a coaxial cable or antenna with a mating RPSMA female
connector.
6.5 Power
One advantage of using the NL240 in your application is its low power
consumption capabilities. With careful planning, you can reduce your station’s
power needs while still meeting your critical communication needs. See
Section 5, Specifications (Power Consumption), and Appendix C.2, Wi-Fi Tab,
for more details.
6.6 LEDs
There are two LEDs on the NL240 that serve as indicators as described below.
Normal Operation
After power-up, the red LED stays solid while the NL240 is searching for and
trying to join a Wi-Fi network (or while creating an ad hoc network).
After joining the network (or failing to join the network) the red LED will
indicate the power mode of the NL240. A double strobe indicates that the
NL240 is in low-power mode. If the red LED stays solid, low-power mode is
not enabled. If the NL240 is in Bridge Mode and the datalogger executes the
IPNetPower instruction, the NL240 will power down and the red LED will
single strobe approximately every four seconds.
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