System Planning
2476_en_I
PHOENIX CONTACT
2-3
2
System Planning
2.1
Accessing the site
To achieve the best radio performance possible, the installation sites have to be given
careful consideration. The primary requirements for a reliable installation include:
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Antenna placement that allows for line-of-sight or adequate signal strength
–
Primary power source that provides required current
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Protection of radio equipment from exposure to weather or temperature extremes
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Suitable entrances for antenna, lightning arrestor, interface or other required cables - if
using remote antennas.
These requirements can be quickly assessed in most applications. A possible exception is
the first item, verifying that a clear line-of-sight exists. A non-obstructed path is ideal;
however, minor obstructions in the signal path will not always block communication. In
general, the need for a clear path becomes greater as the transmission distance increases.
2.2
Path Quality Analysis
With the exception of short-range applications, a path loss study is generally recommended
for new installations. The exceptions include distances of less than 305 m (1000 ft.) where
no test is required in 90% of applications, and where a test is done with a functional Phoenix
Contact radio set to the desired wireless mode, transmit data rate and transmit power
setting. A path loss study predicts the signal strength reliability and estimates the fade
margin of a proposed radio link. While terrain, elevation and distance are the major factors
in this process, a path loss study also considers antenna gain, coaxial cable loss,
transmitter power and receiver sensitivity to arrive at a final prediction.
Path loss studies are normally performed by a communications consultant, wireless
hardware vendor or a system integrator who uses topographic maps or a software path
analysis to evaluate a proposed path.
Although path studies provide valuable assistance in system planning, they are not perfect
in their predictions. It is difficult, for example, to consider the effects of man-made
obstructions or foliage growth without performing an actual on-air test. Such tests can be
done using temporarily installed equipment.
2.3
Signal Strength
The strength of radio signals in a well-designed radio network must exceed the minimum
level needed to establish basic communication. The excess signal is known as the fade
margin, and it compensates for variations in signal level which may occur from time to time
due to foliage growth, minor antenna misalignment or changing atmospheric losses.
While the required amount of fade margin differs from one system to another, experience
has shown that a level of 20 dB above the receiver sensitivity threshold is sufficient in most
systems. RAD-ISM-900-EN-BD… modules provide a means for direct measurement of
received signal strength using a DC voltmeter. Consult Section 6.2, “RSSI (Received Signal
Strength Indicator)” for more information.
RSPSupply - 1-888-532-2706 - www.RSPSupply.com
http://www.RSPSupply.com/p-12970-Phoenix-Contact-2900016-Radio-900-MHz-Ethernet-Radio.aspx
