Wireless-g cards on same machine & channel: interference or negotiation?



  • If I use two wireless-g cards in the same pfsense machine, both set to the same channel and odfm=cts/rts, will they negotiate non-interfering transmissions?  The purpose of this is to obtain more antenna ports (at full power; I want to avoid splitters) because I need additional tightly focused directional antennas.  Or, will the extreme closeness of the two wireless-g cards cause so much trouble that I'm better off using antenna port signal splitters?  Thanks, -pc



  • Two cards like this will most likely cause interference, and so will clients associated to either card. The solution you want is a antenna splitter.
    And if you are on 2.4Ghz you will most likely also like to add passive filters if you run multiple cards on multiple freq.

    The way i solve this is to use up to 3 cards and 3120deg panels, or 2 boxes and 23 cards and 6*60deg. panels, both units using the same channels, then add passive band/channel filters.

    Setup with 6*60deg. antennas and reuse of channels looks like this:

    ch1
                _
    ch11  /      \ ch6
              AP1 with horisontal polarisation mounted about 10 meters (30 ft) lower/higher then AP2
    –--------------------------
              AP2  with vertical polarisation
    ch6    \  _  / ch11
               ch1

    _
    each /     and \ represent the antenna direction.

    In this config i lock the AP to fixed channels and let the clients have a auto setting on channel. I also lock the clients speed (to prevent one client to drag down the speed of the entire AP, I'd rather have a few clients with packet loss then the AP having a max BW of 1mbit or whatever the worst client locks it's speed at). Each channel has the same SSID. and in G mode CTS/RTS is on.

    Hope this info is useful for you.



  • Thank you.  This will be useful for some locations.  Within the city, however, we want to be good neighbors with other wireless providers and the city tech dept.  So, we're attempting to stick with a single channel whenever possible, and we don't necessarily need maximum speed.  At the current rooftop location, we're installing 3 (or 4 slightly overlaping?) 120deg sector antennas; one tightly focused 25deg for backhaul to our primary site, and a second tightly focused 25deg for long distance to another site, all using the same channel if at all possible.  Messy; and, I need to clean it up as much as possible.  I'll use your idea of placing some at different heights.  I read many places that wireless-g cards set to the same channel that can see each other will automatically negotiate taking turns transmitting?



  • It's true that cards/radios that can see eachother will "take turns" but lots of the clients will most likely not see all of them, so your clients will most likely generate "noise" to the other panels/sectors. I'd go with multiple channels or antenna splitters, and for backhaul I'd use 5.X GHz.


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