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Wireless LAN Antennas FAQ'S - Point to Point Wireless

 
What wireless antennas should I use for Point to Point wireless data transmission?

Directional antennas should be used for point-to-point wireless transmission. The type of directional antenna depends upon the power output, cable type and length, height, distance, data rate and terrain. We recommend the use of a range table to estimate the wireless antenna types. Whichever wireless antenna you choose, make sure that it is FCC certified with your radio!


Is the Customer or Client (CPE) system considered Point to Multi-Point or Point to Point wireless?

If the CPE system (or Subscriber Unit - SU) only talks with the POP/AP and is at a fixed location, then it is considered to be Point to Point wireless and can use power and antenna gain associated with Point to Point wireless systems, as shown below. (This has been verified by FCC Certified systems using a 26 dBm radio and a 17 dBi antenna) If a CPE system is part of a mesh network, then it is considered Point to Multi-Point.


Is it safe to work or stand near an active Point to Point wireless LAN antenna?

RF safety is always a concern when working around microwave radiation. The FCC has set safety standards that are meant to guard against potentially harmful RF fields. In a "controlled" environment (where the people near the antenna know of the hazards), the FCC limit is 5.0 mw/cm^2. In an "uncontrolled" environment (where the people near the antenna are unaware), the FCC limit is 1.0 mw/cm^2. These limits are directly related to the EIRP of the antenna system along the main beam. Other frequencies and powers may be calculated at this site: RF safety Here are some other excellent links: ARRL - RF Exposure, ARRL - RF Safety, FDA, WLANA - Health

At 2450 MHz

EIRP of antenna system
(dBm)

Min. Safe Distance in a Controlled Environment
(feet)

Min. Safe Distance in an Uncontrolled Environment
(feet)

36
0.31
0.63
40
0.46
0.98
42
0.57
1.22
44
0.71
1.52
46
0.88
1.90
48
1.09
2.37

 

How do I perform a Point to Point wireless site survey?

Initially, create a path profile using one of the various mapping programs. If LOS and Fresnel zone clearance seems good, check for trees and other unusual obstacles to LOS. A good way to check this is to place a person at each end of the path with a high-powered flashlight and a cell-phone. While talking with each other, flash the light so that the other person can see it. UHF hand-held radios (FRS or commercial frequencies) also work well to determine LOS. Use 1 watt radios for up to 4 miles and 5 watt radios for up to 15 miles. If results look promising, place an AP at one end and a CPE at the other and try connecting using 19-24 dBi grid or panel antennas. (Do not swing both directional antennas at the same time!) Look for interference at each end by using a spectrum analyzer and both vertical and horizontal polarized antennas. If you have Teletronics radios, here is a neat site-survey tool. There are also professional consultants (e.g. Cyber-Doctors) that can perform wireless site surveys for a fee. Wireless site survey tools are available on the AeroNet wireless broadband site.


What is the Maximum Distance for a Point to Point wireless link?

The maximum distance for a standard 802.11b Point to Point (or Point to Multi-Point) path is approximately 12 miles. This is primarily due to timing issues in the 802.11b firmware. Other operating systems, such as KarlNet TurboCell, Orinoco COR or StarOS can overcome this limit and produce links up to 70 miles, depending upon terrain.