Tips on Site Surveys and Installation of 802.11 Wireless LAN Access Points and Accessories
By Joe Mehaffey

Well,  I wish deciding where to put AP in buildings was an exact science and I could tell you exactly how to proceed.  But.. It is not that easy.  Unfortunately every building is different and while we can PLAN how things might work inside a structure,  a site survey after the building is built is the only way to INSURE that all necessary areas are covered completely by Wireless LAN signals..  

Here are some things to consider:
1) Call backs are EXPENSIVE and my experience with cheap APs is that there seems to always be "something"  wrong with them and just a few callbacks and you have spent your profits.  In your own home installation where you can "mess with equipment" if it does not operate properly, the cheap units are good buys and serve knowledgable users well and cost effectively.  With reference only to wireless 802.11 gear,  I have had good results with Cisco, SMC, and Senao  while Dlink and LinkSys brands have been less reliable.
2) The average PCMCIA card has an output of about +17dbm (50mw) and so it does you no good to have a 500mw transmitter on one end (the access point) and a 50mw transmitter on the client end (laptop).  Transmit power should be balanced. Since there are some good 100 and 200mw client cards out there, a good design goal for your AP is around 200 to 300mw output BUT ONLY if you are using 200mw cards in your laptops.  Gain antennas are GOOD and a 6db higher gain antenna on just ONE end of a circuit (say on the AP end) will double the range of the system since it receives AND transmits with equal gain.
3) Stay away from the current WRT54g Linksys AP as it periodically "locks up" on short power glitches.  It was worse until the midsummer firmware update and that helped it a lot.  However I have had one additional lockup on the new firmware.  The symptoms are that you can communicate with the unit on the wired side just fine, but there is no RF output.  A power down/reset is necessary to get it going again.  Linksys does not seem to consider this a serious problem, but I do.  The WPC54g card works fine but not if you want to do automatic drive mapping during boot time as mentioned in my article.
4) The QUALITY equipment is Cisco but I don't know if they have 54g equipment out yet.  They sometimes have problems but then FIX them!
5) I have tried out the SMC 2804WBR and the PCMCIA card SMC2835W.  Both work very well and are easy to setup.  In temperature testing with the SMC-2804WBR,  I found it shuts down (and does not self recover) if the temperature exceeds 120F.  No other unit I have tested has failed to operate over its specified temperature range.  SMC techs said I was free to send it in for exchange, but they doubted I would see any improvement.  So I put this particular unit to work in a client's basement where I am sure it will live happily.
6) I like the Dlink 54g card but it seems to have problems on any DELL brand computer unless it is running XP and then it works fine.  Works OK on Toshiba but other brands I do not know about.
7) Senao has a 2511CD PLUS card that has 200mw output (802.11b).  If you use (say) a Cisco 240 AP (50mw) with a 10db amplifier from, you about double to triple the range of the 50mw cards/AP combo.  Senao is said to be  "soon" going to have a 200mw 54g card and these folks seem to do a nice job.  EnGenius 200mw is a rebrand of the Senao product.
8) When you do a site survey think about the fact that 802.11 signals are very low power and do not readily penetrate many building materials.  Consider the following when designing a large 802.11 wireless LAN installation:
    a) brick, metal siding, metal screens in windows/doors, metal doors, some concrete siding, some wood siding and cellulose insulation in walls all severely attenuate signals at 2500mhz.  Frame houses will generally have more penetration of signals than brick houses but you won't know for sure until you check. Frame "looking" houses might be aluminum siding and aluminum foil backed  insulation can sometimes be found inside walls where you would never expect it.
     b) 2500mhz 50mw signals will pass thru about TWO normal sheet rock walls before being excessively attenuated.  After two walls,  you will find that the system will work some places and not others and I can't predict without an actual site survey which will be good/bad.
    c) Generally, try and put the AP and its antenna inside the living space protruding from a ceiling.  Dropped ceilings are good.  If you cannot find a ceiling spot,  you can put the AP in a closet or attic  but remember you are already signing up for attenuation thru the attic floor.  Also remember that when you look "sideways" at a shallow angle (say 45 degrees) from an attic, in one direction perpendicular to the ceiling joists, you are looking through a LOT of wood.
    d) concrete floors in multistory buildings are essentially not penetrated by 2500mhz signals.  At least,  do not COUNT on it working on the other side of a concrete wall, floor or ceiling.
    e) If you use Cisco 350 series bridges (or other repeater/bridge techniques) you do not have to string wires as these devices can  "repeat" signals.  BUT.. If you do this, at each REPEAT, you only have HALF  the thruput left.  IE.. A user operating directly on the main AP gets 11mbps.  Then out of the first repeater he can get only 5.5mbps.  If  there is a second repeater and our user operates through it to the first repeater and then back to the AP,  he will be down to about 2.75mbps maximum theoretical throughput.
9)  If you do use gain antennas you have to consider the antenna PATTERN.   For instance,  if you use a high gain omni directional antenna on a tower or high structure,  the antenna may have very little signal at ground level around the tower unless your "looking up at the tower" elevation angle is less than maybe 20 to 30 degrees.  If you buy a high gain antenna, ask for a specification sheet and look carefully at the antenna pattern specs and see if it meets your needs.
I suggest you not try and install RJ45 male connectors in the field but rather use jacks in the wall/on the wall and premade patch cables to connect to devices like routers and APs.  The reason is that I find that field installed RJ45 plugs are prone to go open and cause service calls.   (If someone knows product and technique for field installing RJ45 plugs in a reliable manner, PLEASE let me in on it!)
I suggest you run multiple cat5 cables to everywhere you MIGHT want to have an access point in new construction.  Wire goes in EASY while the walls and ceilings are open and HARD and time consuming later.

Have fun!  Wireless is fun,  but it can be frustrating..

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