Help Please : AP and Antenna



  • Hi,

    Sorry to ask again, but im not sure i phrased myself too well last time hence the lack of replies - ill be direct this time.

    Can pfSense running on a small form factor PC work as an AccessPoint with the addition of a good wireless card - or do i still need a seperate access point?
    Assuming I can just add a wireless card into my machine, can i connect an external antenna - either an internal (inside the buiding, not inside the machine ) or an external ( outside in the open)  ?  Is there a maximum cable run?

    I was thinking of using a WRAP based solution, but feel that i should offer some form of content filtering which i assume limits me to PC based?

    Any advise much appreciated - im looking to roll out circa 100 solutions free of charge and recoup my investment via the hourly / daily / weekly signups.

    thank you.



  • You don't necessarily need an external access point. pfSense can do this with a good wireless nic (like atheros based cards) installed.

    Of course you can connect an external antenna to your wireless nic.
    Depending on your needs of coverage an inhouse antenna might be preferred agains an outdoor variant. Get the antenna closest to where coverage is needed. If it's on the outside of a building go ontop of the roof but don't forget correct grounding (lighting). It might be easier to put a wrap box in an outdoor housing on your roof since you only need to run a CAT5 with PoE up there.
    There is no such thing as a maximum antenna cable run. This depends on the nic, the cable itself and the antenna - together with the needed performance. You will lose signal on the cable. If it's getting too much you can add a booster to compensate for this loss. Depending on your location you might need to take care not to exceed the maximum allowed ERP, though.

    The antenna itself can be (highly) directional or omni.
    Directional antennas like yagis usually make sense when connecting two locations. Omnis when covering a large area. Think of a donut shape for an omni with a deep notch on top and bottom of the antenna.
    The higher the gain of an omni the more donut  ;D



  • Many thanks for the answer, much appreciated.

    regards

    David



  • Antenna boosters sometimes are called "compenser" as well. They compensate for cable loss usually in both directions.

    For Atheros based NICs in AP mode have a look here:
    http://forum.pfsense.org/index.php/topic,5582.0/topicseen.html

    @candengo:

    I was thinking of using a WRAP based solution, but feel that i should offer some form of content filtering which i assume limits me to PC based?

    Right, you cannot run packages on embedded installs. Squid and Snort usually require more hardware resources than a WRAP or Soekris can offer. But both aren't available in large quantities any more and will be replaced by beefier hardware in the future. That might be another option if you can wait.



  • Thanks Chris - very helpfull.

    Can anyone recomend a UK based supplier for the Atheros based Wireless cards?



  • if you have a long antenna cable and need a booster: you could also use a card that has from itself a higher output power like this atheros based cards from compex (up to 400 mW / 26dBm)
    http://www.compex.com.sg/home/index.asp

    for a shop that sells them:
    http://pcengines.ch/order.php



  • @GruensFroeschli:

    if you have a long antenna cable and need a booster: you could also use a card that has from itself a higher output power (up to 400 mW / 26dBm)

    This is NOT the preferred way to do it!
    You always wanna put the booster closest to the antenna.

    If you only look at the transmitter side it doesn't make a big difference. If you calculate the receiving side of your AP the difference is obvious:

    • adding gain at the antenna increases signal and noise alike. Both will be damped on the cable run with the same amount resulting in a constant signal/noise ratio.
    • feeding the signal directly down the cable decreases it. Noise stays the same and results in a much decreased S/N ratio 'down there'. Boosting it gives you more signal and more noise as well and the bad S/N ratio stays the same - only at higher levels! Additionally this might lead to other unwanted effects especially if you are in somewhat noisy environments (from an HF view).

    Granted, there are scenarios where it does work flawlessly. If you need wider coverage and expect signals to arrive with low levels at the antenna, you will think about this again…

    Bottom line: do it right from the beginning



  • Actually the amped card is better then a external AMP, And the reason is simple, the amp cirquits on the board has a better SNR ratio then adding a external amp via cables that will act as a antenna and pick up even more noise. As for placing the AMP closest to the antenna, this is mostly usefull if the AMP has AGC(Automatic Gain Control), if not it's actually better to put it closest to the card. ( I'm sure we can have a long discussion about all the why's and hows etc.  ;D )

    But the best way to AMP a signal is allways by adding a suitable antenna, by suitable I mean a antenna that gives you the gain you need with the narrowest radiation pattern you can live with.

    -lsf



  • @lsf:

    But the best way to AMP a signal is allways by adding a suitable antenna, by suitable I mean a antenna that gives you the gain you need With the narrowest radiation pattern you can live with.

    I absolutely second that!

    For the rest of the post I stick to what I said and do not open Pandora's box.

    On a side note I found a receiver booster which only boosts from the antenna down the cable. Together with a raised output power from the card this can make sense as well. But I have no experience with this unit!


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