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TECHNOLOGY INFORMATION
What about line of Site?
The technology and frequencies used by Rapid WiFi's wireless antennas
requires a clear path between antennas. This is called Radio Line of Sight,
or LOS.
Line of sight is the direct free-space path that exists between two points. Using binoculars on a clear day, it is easy to determine if visual line of sight exists between two points that are miles apart. To have a clear line of sight there must be no obstructions between the two locations. Often this means that the observation points must be high enough to allow the viewer to see over any ground-based obstructions.

The following obstructions might obscure a visual link:
  • Topographic features, such as hills or mountains
  • The curvature of the Earth
  • Buildings and other man-made objects
  • Trees and other vegitation

  • If any of these obstructions rise high enough to block the view from end to end, there is no visual line of sight.
    Line of Site Blocked
    Obstructions that can interfere with visual line of sight can also interfere with radio line of sight. But one must also consider the Fresnel effect. If an object, such as a building, hill or tree, is too close to the signal path, it can damage the radio signal or reduce its strength. This happens even though the obstacle does not obscure the direct, visual line of sight.

    The Fresnel zone for a radio beam is an elliptical area immediately surrounding the visual path. It varies in thickness depending on the length of the signal path and the frequency of the signal. The necessary clearance for the Fresnel zone can be calculated, and it must be taken into account when designing wireless links.
    Line of Sight Blocked
    As shown in the picture above, when an object protrudes into the signal path within the Fresnel zone, knife-edge diffraction can deflect part of the signal and cause it to reach the receiving antenna slightly later than the direct signal. Since these deflected signals are out of phase with the direct signal, they can reduce its power or cancel it out altogether. If trees or other 'soft' objects protrude into the Fresnel zone, they can attenuate (reduced the strength of) a passing signal. In short, the fact that you can see a location does not mean that you can establish a quality radio link to that location.

    For short links of two miles or less, you can determine radio line of sight by climbing to the proposed antenna mounting point and looking for the other site with the aid of binoculars. If you can see the destination point, you can calculate the Fresnel zone allowance by consulting a reference table, or using the calculator below. If any obstacles (buildings, trees, etc.) in the Fresnel zone between the two points could interfere with the signal, the calculation for the antenna height must take these obstructions into account.

    Rapid WiFi uses computerized maps provided by the US Geological Service to make a preliminary assessment concerning the feasibility of a radio link between two points. Where the preliminary finding leaves any doubt, it is the customer's responsibility to engage the proper resources to certify that radio line of sight for the desired frequency is possible and what the antenna heights must be. You may also request a free site survey to determine if a radio link is possible.

    There are several options to establish or improve the line of sight:
  • Raise the antenna mounting point on the existing structure
  • Erect a radio tower tall enough to mount the antenna
  • Increase the height of an existing tower
  • Change the mounting point for the antenna, i.e. building or tower
  • Cut down or top problem trees

    For more information and pricing on this innovative and exciting new service, please feel free to contact us.
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