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WiFi Antennas


									WiFi Antennas

        Reid Palmeira
WiFi Specification
   IEEE 802.11b
         Uses 2.4 GHz frequency band
         Up to 11 Mbps
         Has fallback data rates to 5.5, 2 and 1 Mbps
         Uses only Direct Sequence Spread Spectrum
         Approx. 200 ft. clear line of sight range
         14 total channels, 11 channels (in US)
   Pringles can
       Effective directional antenna
   Cantenna
       More effective
   Parabolic dish
       Much more effective
       Significantly improved SNR
       Limits the useful range of WiFi
Legality Disclaimer
   Illegal by FCC regulations
       You can only attach an FCC approval
        antenna to a WiFi card or base station
       Only commercial antennas are approved
       Enforcement provisions are minimal
Design Considerations
   Effectiveness
       SNR improvement
       Signal range improvement
   Size
       Portability
       Storage
   Cost and Build Time
       Realistic use
       Accessibility
   Legality
       If the FCC comes knocking, be French: run away!
   N-Connector and pigtail from the reflector
    (the can) to the AP or to the WiFi card
   Mount the injector to the side of the reflector
   Parts must be checked to make sure
    matching errors don’t occur – for example
    standard coax cable from something like a TV
    will absorb the entire signal very quickly.
   The longer the reflector (the can) the more
    directional and less omni-directional the
    antenna becomes
Benefits of can type booster antenna

   Improved SNR and performance
   Increase in effective range of WiFi
   Cost is much less than commercial
    antenna with similar performance
   Build and testing times are small
Parabolic Antenna
Design of Parabolic
   Shaped wire mesh bent over a parabolic
    frame to form a miniature grid antenna
   Mesh material should be such that
   Attached to the AP
   Focal length varies proportionally with
    the size of the mesh dish - scalability
Benefits of parabolic design
   Increased security, since signal degrades
    behind the parabola
   Minimal parts and build time
   Significant reduction of interference
   Less parts and no N-connectors, pigtails or
    cables means no matching problems or
    transmission line worries
   No modification of any WiFi cards or
    modification to parts of the AP
Testing with Network Stumbler

                  Green is signal
                  Red is noise

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