Do I need antenna for my minipci wireless CM9?



  • Hi.

    I got a mini-pci atheros CM9 in my alix board, this is the first time I work with a mini-pci wireless card, I setup the card and everything looks good and working, but the I lost the signal at 5 meters, is a rule that I need a antenna?

    I have change different parameters but the same behavior.

    Pfsense 2.0, thanks.



  • try to listen radio without antenna.. same thing -> you really need antenna



  • Hi.

    Thanks Metu69salemi, I ask this because u normally purchase a radio and u receive everything, now u go and got a firewall with a mini-pci wireless but the seller doesn't offer u the antenna, them I purchase the whole package and I was curios about this, but I wanted to find it my self, it cross this question in my mind, after testing I see this small issue and just wanted to get a strong answer from people with more experience in this field.

    Now u clarify my doubt, next time I got to get the whole package with antenna, thanks again  :)



  • You welcome. I think that they didn't offer you an antenna, because how they should know what you need. there is lot of different kind of antennaes, variations comes from: radiation patterns and signal strength as an example



  • Now I will go deep in this field, I have to read and learn about antennas, thanks again!!!



  • you might want to read this http://forum.pfsense.org/index.php/topic,43501.0.html (especially the last few lines).



  • Let me try to give the condensed, simplified version:

    1. Figure out your country's wireless channel rules (perhaps start at http://en.wikipedia.org/wiki/List_of_WLAN_channels)

    2. Figure out which band you want to use - 802.11a in the 5.1 to 5.2Ghz area (channels 36,40,44,48 or so), 802.11a in the 5.7 to 5.8Ghz area (channels 149,153,157,161,165 or so), or 802.11b/g (2.4Ghz), or if you're going to try both.  Almost everyone in the U.S. uses 2.4Ghz, which has only 3 channels that don't overlap (1, 6, and 11).  The two 5Ghz bands are mostly free, and none of their channels overlap with each other… but it doesn't go through walls and trees as well.  Antennas are made for one, two, or all three bands; if you can stick with single band antennas, it's simpler and easier to find them.

    3. Figure out the shape of the area you need to serve.

    3a) Omnidirectional verticals: These look like a stick or a "rubber duck" antenna, and are what you commonly see, and provide a 360 degree circle of coverage... in the horizontal plane.  In general, a "low gain" (small number, like 3 or 5, in front of the dBi) antenna provides a larger "wedge" of coverage in the vertical plane, while a "high gain" (large number, like 9 or 12, in front of the dBi) antenna provides a smaller "wedge" of coverage in the vertical plane.  For instance, a low gain antenna on a rooftop might not reach to the edges of the yard, while a high gain antenna would... but people sitting down in the middle of the yard might not get signal, because the "wedge" of "strong enough" signal would be above them.  These are all "vertically polarized" (see 3b).

    3b) Directional or sector antennas: These look like a flat panel, or a satellite dish, or 1/4 of a cylinder, or a sort of like a very small old-style rooftop TV antenna, or sort of like two very small bent TV antennas put together, or a Pringles can, or...  These have a greater capability in "front" of them, or within the "sector" of coverage, and a much lesser capability outside of that area of coverage.  The higher the dBi, the narrower the area of coverage.  This can be a good thing; for instance, if you put this type of antenna up on your sourthern border, facing north, it's going to be much less likely to pick up someone else's wireless traffic on the other (even more southerly) side of the street.  There are quite a few 90 degree or 120 degree "sector" designs that may do well if you put your access point in the corner of the house.

    3bi) Polarization: For directional antennas, most can be oriented for vertical or horizontal polarization (and a few use circular); match your entire setup to one or the other, because crossing polarization costs you a lot of signal.  Vertical is the most common, so if you can use horizontal, you'll help reduce interference; both others interfering with you, and you interfering with them.

    1. Antenna cable: This is a source of loss, so keep your cables short (inches, not yards).  Chances are, you'll want a U.FL to RP-SMA bulkhead connector pigtail, plus either an RP-SMA cable to go to your antenna, or an antenna with an RP-SMA connection which you'll screw directly onto the bulkhead connector (just like the consumer wireless devices).

    2. Power.  Use as little as you actually need to meet your needs, both at the access point and your devices - pfSense lets you turn it down, and it can be quite impressive to see basement to corner of the yard connections at a power level of only 66 (and much lower just inside the house).  External USB cards with external antennas can be very helpful, too.  If you think you need more power or a high gain antenna, look up your local jurisdiction, but there are rules about high gain antennas on high power WiFi devices, and they say: Thou Shalt Do The Math.  Don't put a 12dBi Omni on a "High Power 1000mw" card at maximum power!

    5a) Antenna >> Power.  A better antenna lets you send better, and receive better.  More power only lets you send better.



  • Great list. I would add:

    1. Consider both access points and clients. For example, a directional antenna on a client might be a good way of reducing interference from a close neighbour.

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