RF Neulink NL900S - Manual (Page 5)

NL900S USER MANUAL 5
1.0 Introduction
The NL900S series transceivers provide highly reliable wireless connectivity for either point-to-
point or point-to-multipoint applications. Frequency hopping spread spectrum (FHSS)
technology ensures maximum resistance to multipath fading and robustness in the presence of
interfering signals, while operation in the 900 MHz ISM band allows license-free use in the US
and Canada. The NL900S supports all standard serial data rates for host communications from
1.2 to 115.2 kb/s. On-board data buffering and an error-correcting air protocol provide smooth
data flow and simplify the task of integration with existing applications. Key NL900S features
include:
• Multipath fading resistant frequency hop- ping
technology with up to 50 frequency channels
(902 to 928 MHz).
• Support for point-to-point or point-to-
multipoint applications.
• FCC 15.247 certified for license-free
operation.
• 20 mile plus range with omni-directional antennas
(antenna height dependent).
• Transparent ARQ protocol with data
buffering ensures data integrity
• Selectable 1, 10, 100, 250, 500 or 1000 mW
transmit power with a firmware interlock of
85 mW maximum for 500 kb/s operation.
• Optional AES encryption provides
protection to eavesdropping
• Nonvolatile memory stores NL900S
configuration when powered off
• Simple serial interface handles data up to 115.2
kb/s
1.1 Why Spread Spectrum?
A radio channel can be very hostile, corrupted by noise, path loss and interfering transmissions
from other radios. Even in an interference-free environment, radio performance faces serious
degradation through a phenomenon known as multipath fading. Multipath fading results when two
or more reflected rays of the transmitted signal arrive at the receiving antenna with opposing phases,
thereby partially or completely canceling the signal. This problem is particularly prevalent in indoor
installations. In the frequency domain, a multipath fade can be described as a frequency-selective
notch that shifts in location and intensity over time as reflections change due to motion of the radio
or objects within its range. At any given time, multipath fades will typically occupy 1% - 2% of the
band. From a probabilistic viewpoint, a conventional radio system faces a 1% - 2% chance of signal
impairment at any given time due to multi- path fading.
Spread spectrum reduces the vulnerability of a radio system to interference from both multipath
fading and jammers by distributing the transmitted signal over a larger region of the frequency
band than would otherwise be necessary to send the information. This allows the signal to be
reconstructed even though part of it may be lost or corrupted in transmission.