Solectek skyway series, User Manual

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Antennas
Antennas come in different configurations to serve different needs. To span large dis-
tances, you must narrow the signal into a focused beam. The more focused is the sig-
nal, the greater is the gain. Since narrowing the signal increases the gain, you are
allowed to exceed six dB only if you reduce the power to less than 1 watt under FCC
rule Part 15.247. On the other hand, a 360
o
omnidirectional antenna has only a four-
fold gain, so it can use the maximum allowable one watt of power.
Antenna Types
Directional. A directional antenna focuses the signal into a narrow beam. For 2.4
GHz systems, dish antennas achieve the highest gain and span the greatest distances.
Solectek’s dish antenna has 21 dBi of gain, and when using a transmit power of 15 dBm
(a small fraction of one watt) the EIRP is 36 dBm (the FCC maximum allowable). In the
902-928 MHz range, yagi antennas achieve the highest gain and span the greatest dis-
tances.
In addition to concentrating signal strength, directional antennas also:
• Reduce the strength of second Fresnel zone reflections, thus reducing the
potential for interference.
• Reduce interference from other RF devices within the same frequency range
at distances closer than the target antenna.
Multidirectional. Multidirectional antennas are used for connections where several
interfacing antennas are located in the same general direction. To achieve directionality
with a 2.4 GHz system, Solectek uses an antenna with a sectoral. Because multidirec-
tional antennas have a more focused beam than omnidirectional antennas, they
achieve higher gain and have greater spanning distances.
Omnidirectional. Omnidirectional antennas are used for connections where the
interfacing antennas are located in opposing directions. Because the focus of an omni-
directional antenna is 360 degrees, it has less gain and spans a smaller distance than
other types of antennas.
Antenna Alignment
Antenna Polarization. To improve the isolation between adjacent antenna installa-
tions, in addition to using different channels, you can change polarization. Consult your
Solectek systems engineer for specific details.
Fresnel Zones. Waves can be deflected by objects in their paths. If a wave from an
outer band of the cone (see Radio Signals) is deflected back through the center lobe, it
can either strengthen that signal or reduce its strength, depending on how the waves