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New Member

AP 1140 Interference

Hi,

We have AIR-LAP1141N-E-K9, that will be installed above false ceiling made of "perforated aluminum" with 1mm thickness with 17% open slotted surface.

What would be the level of interference and signal loss?

Many thanks,

Yazeed


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6 REPLIES

Re: AP 1140 Interference

Yaltal,

This is where a wireless survey should be done. You'll need to make a specific assessment of your ceiling material attenuation, scattering and blocking characteristics.

You can do a quick test rather inexpensively by placing an AP in the desired location and then measuring RSSI with a free tool like InSSIDer. Walk around and note signal drop off as you're moving away from the AP. This will give you a sense of the signal loss over distance.

You will also need to measure goodput, which you do with tools like speedtest.net or you can see how long it's taking to copy large files from a wireless client to a server. For this test you can compare file transfers when the AP is above the panel vs. when it's just sitting on a table (for example).

These methods are not a substitute for a professional wireless survey, but they will give you a broad brush-stroke sense of whether the aluminum panels are outright killing your signal.

Justin

Sent from Cisco Technical Support iPhone App

New Member

AP 1140 Interference

Thanks Justin


The site is still under construction and the material is not available yet. So no way to do survey now.

If anyone has experience with above quesiton please share it.

Many thanks,

Yazeed

Re: AP 1140 Interference

Yazeed,

The widespread experience among wireless engineers is pretty much what Leo is saying--metal screens and panels are a wireless killer.

Perforated aluminum ceiling panels are going to severely degrade your signal. At 17% open space in a 1mm thick sheet, you have mostly metal with a bunch of small holes or slots. Look at the door of your microwave oven. There is probably 40% to 50% open space on the door grille, and yet an insignificant amount of microwave energy escapes the oven.

Actual energy loss is a function of size and shape of the openings, the wireless frequency, panel thickness, material composition, radiator distance from the panel, etc., which is why a wireless survey of the actual environment is of critical importance when you're dealing with metal in spaces where you want to deploy WiFi.

For planning purposes, you should assume that you cannot mount your 1141 AP above the aluminum ceiling panels unless all you want to do is heat the airspace there get nothing else out of it. I recommend that you consider alternative solutions such as mounting your APs below the ceiling plane or using patch antennas mounted on the (hopfully not metal) walls and attached to 1260, 3502e or 3602e series APs.

If you are in a position where you need to mathematically justify this rationale and you want to get a rough numerical sense of what you're up against, google around for an RF shielding effectiveness online calculator. Clemson has a good one (with aluminum as a selectable material) and there are a few others.

Justin

Hall of Fame Super Gold

AP 1140 Interference

We have AIR-LAP1141N-E-K9, that will be installed above false ceiling made of "perforated aluminum"

I just read up to this point and my answer would be "how about 100% signal loss".

Wireless and metal don't mix.  Hiding your WAP above the false ceiling or putting a metal sheet between a WAP and your client will cause the metal to DEFLECT your wireless signal away from the client.

You've seen the movie Captain America?  You saw the scene where he uses his shield to deflect bullets? 

New Member

Re: AP 1140 Interference

You would think that if the ceiling tile was 17% open you would probably get 17% of your RF through but that may not be the case.  The slots would have to be big enough to pass the full wavelength which for 2.4ghz is 4.92".  Smaller and who knows what you'll get. If the slots are 1/2 the wavelength then you'll create standing waves and have a resonant tuned ceiling tile.  Well maybe, I really don't remember all this crap from my Navy Electronic Warfare days but we used to use aluminum foil to wrap our antennaes in order to block all RF while in port to do testing, calibration and maintenance.

There's got to be other locations for the APs.  Most are slick looking enough to be left in plain sight mounted on a wall somewhere and the are the ceiling recess mounted types but I doubt they'd want to break up the tin ceiling for that so I would do on the walls in plain sight or in closets or other inconspicuous locations. 

New Member

Re: AP 1140 Interference

This was posted today(?) and pretty much explains AP deployment and RF antennae principles.  Do & don'ts which you really should watch.

https://supportforums.cisco.com/videos/3356

You don't have to log in to view it so if there are architects, designers or the clients themselves that are pushing the installation above the metal tiles in the plenum rated void above the ceiling then let them watch this too. 

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