I’ve been reading this ´old´ thread and still have some important remarks to make that seems not to have been discussed:
What is the channel separation between the radio cards in one box? I see two cards mentioned to work in 5,4Ghz and one as AP in either 2,4 or 5,4Ghz.
The ´normal´ 5Ghz band is 200Mhz wide (5500 to 5700Mhz) and if you use 20Mhz channel you can create 11 channels each 20Mhz apart. If channels inside one box are choosen smart you can keep at least 20, but better 40 or even better 60Mhz distance between radio’s.
If the 3rd card is also in same 5Ghz band than you have to spread the 3 radio to the best over the band.
If you only using 5,4ghz (which band is that? In europe it is forbidden for wlan) than you have only one freq. channel to spare. Using it for more than one radio is asking for problems.
But, another factor that is not discussed: When using ´n´ with upper or lower channel the actuall radio frequency bandwith the radio uses is increased to 40Mhz! You can understand that now suddenly the 5ghz band only has room for 6 free channels! In the 2,4Ghz you use the whole band spectrum!
To keep these away with sufficiant spectrum inbetween from other radios becomes a task now if many AP’s are used in same spectrum. Let alone if other ´boxes´ in the area are to use their own radio channels while they still can ´see´ eachother…
Now, on top of all, if also TDMA is used (nv2) things even become worse. Out of experiance I found that adjacent channels best would be kept 40Mhz away from eachother even on distant but reachable AP’s.
(It seems that stations leaving an AP in one working channel trigger other AP’s in adjacent channels to shut down some units as well at times. Although it now looks ros5.1 is doing much better in that respect.)
If the same nv2 would now have to be applied to 40Mhz wide ´n´ links it becomes almost inevitable to have interference problems.
I live in a valley where basically all 30 AP’s (AP’s plus backhaul links, mine and others) using the 5Ghz band. They all tend to interfere with eachother. Only one year ago I was sort of the only with half the amount of radio units in this band and all 802.11a. In these days I hardly had problems…
Since others started to use Airmax (UBNT, tdma + ´n´!) and I nv2 and some ´n´ backhauls things became a bit hectic.
Random disconnects all over the place up to complete crashing units that have been running for months or even 2 years! (After 3 months of struggling I sort of found that UBNT tdma protocol interferes more with legacy ubnt units (I have them in my network) while MT’s nv2 is more problamatic for other ROS running devices.
To battle all this I am now removing all ubnt devices because it seems I can’t bring them under control (since I have no control over ´other’s´ networks) and for AP’s I am now putting cards in separate metal (or spray painted plastic) box and started to use 10Mhz channels on my AP’s.
I am in the process of converting all my AP’s into nv2 running as well and ´harden´ all links by setting the frequency in the stations ´scan´ list, make sure both mac address and SSID are mentioned of the AP in the stations ´connect to´ list (separate rules), use very limited data and basic connection rates and setup security on the nv2 links or the man. protection on the 802.11a links.
This brougt my network back into stability.(I must state here that also the use of ros5.1 brought lots of improvement to my network. Obviously the drivers must have been improved to better withstand interference issues.)
If you use ´n´ protocol link with nv2 on 2,4ghz you basically consume the whole band for that unit only. If you use it on AP’s use only channel 1 and 11 (or 12, 13 or 14 depending on your region) and shield everything in your transmission/recieve line as good as possible from other radio signals. Like said, use good materials, sector antenna instead of omni, one card-one box etc.
Regarding the isolation of each radio card with metal paper wrapping I have to mention the possible risk that comes with it:
- Shortcuts! Be very carefull with the placing. It should not contact any conductive parts of both the board or the radio cards! (Don’t even think of fitting it while board is powered up!)
- Heat dissolvement. Wrapping radio’s in prevents the heat to dissipate. This is also a very good argument not to use too many cards in one box anyway. If you have one or two HP cards running in a box that is in the full sunlight all day and you don’t have sufficiant ventilation expect the radios to drop in the heat of the day and it shortens the live time anyway considerably. Let alone if you now give the radio’s an extra warm ´coat´!
So, the magic word is “separation”!
Separation of radio signals. (good earthed and shielde coax. Also the little pigtails that connect to the card!)
Separation of radio cards
Separation of complete units
Separation of antenna’s
Separation of working channels.
Somewhere on this forum a guy did some test on two cards in one box and you’ll be amazed how much interference and how far it carries (in the band) you’ll find! !0Mhz for the AP already reduces the ´footprint´ of that radio, even IN the box!
