Verint Nextiva S1100, Руководство пользователя

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2: System and RF Planning
16 Verint Video Intelligence Solutions
The region outlined by the signal beam width is known as the first Fresnel zone. The
Fresnel zone is always thicker at the mid-point between the two antennas. Therefore what
appears to be a perfect line-of-sight path between the base and a remote station may not
be adequate for a radio signal; this is the difference between “visual” and “RF” line of sight.
In practice, it has been determined that a radio path can be considered an RF line-of-sight
path if it has a clear opening through 60% of the first Fresnel zone (or 0.6 F1). Here are
values for 0.6 F1 for various signal path distances and frequency bands:
For distances under seven miles, the earth curvature effect is negligible. However, for
greater distances, you need to consider it in your calculations; for instance, for a 15-mile
link in the 2.4 GHz band, the two antennas must be located 82 feet higher than the highest
obstacle in the RF line of sight between them (that is, 53 feet for the Fresnel zone plus
29 feet for the earth curvature effect). For help, consult the Verint Video Intelligence
Solutions Support group.
A common problem encountered in the field and related to the 0.6 F1 clearance rule is
building obstruction. The proposed visual path may just barely clear a building but the RF
line of sight will not. In such a case, the signal will be partially absorbed and diffracted.
Increasing the height of the two antennas or the gain of the antennas are the only
alternatives to improve the link quality.
Note: At 2.4, 4.9, and 5 GHz, radio waves are highly attenuated by dense foliage. A link
established in the fall or winter season may be adversely affected in the spring and
summertime, if it is established below tree level.
Distance
(mi./km) 2.45 GHz
(feet/m) 4.9 GHz
(feet/m) 5.3 GHz
(feet/m) 5.8 GHz
(feet/m) Earth curvature effect
(feet/m)
1 / 1.6 14 / 4.2 9.8 / 3.0 9.5 / 2.9 8.9 / 2.7 0
4 / 6.5 27 / 8.4 19.5 / 5.9 18.7 / 5.7 18 / 5.5 2 / 0.6
7 / 11.3 37 / 11 25.8 / 7.9 25 / 7.6 23.6 / 7.2 6 / 1.8
15 / 24 53 / 16 37.8 / 11.5 36.4 / 11.1 35 / 10.6 29 / 8.8
Visual line of sight First Fresnel zone (F1)