AiroNet AP 1200 / SNR Flapping / Small Coverage

Unanswered Question
Mar 22nd, 2007

After Implementing an autonomous AP 1200 series and making the basic

configuration, I ran Aironet Desktop Utility from my laptop to see the

signal strength,

I noticed that SNR (Signal To Noise Ratio) was decreasing suddenly

from 50 db to 12 db then after 10 sec it increased to 30 db then

decreasing to 8 db and so on..

I was standing in my place , I didn't move my laptop , and the AP was

fixed in the wall with 2 diversity small Dipole antennas, I tried to

change the AP many times with another Aironet 1200 but the problem was

still exist !!!!!

Finally I replaced my Cisco AP with D-link one and every think was OK

There wasn't SNR flapping, and the coverage area was much better,

Because I'm sure that Cisco product is better than D-link I need

your help to solve this problem.



I have this problem too.
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bstremp Wed, 03/28/2007 - 11:40

One possible reason that I can think of is radio frequency interference. There could be some other wireless device in the same frequency range that is intefering with your RF signal. The reason that the other AP works is that it may be using a different frequency range.

d-mercado Sun, 04/01/2007 - 05:07

Hi Bstremp,

Actually what i did is I configured the AP to use the least congested channel so it can't be an interference problem.

Thank you,


scottmac Sun, 04/01/2007 - 08:44

It can ALWAYS be an interference problem. Interference (and multipath) is #1 for "Why doesn't my AP work well."

While "auto" functions occasionally / frequently work well, your best practice to make sure you're getting optimal performance is to set it up manually.

Download and run NetStumbler ( - it's free) and see what the interference and channel usage is for your coverage zone.

Choose a channel from 1, 6, or 11 (assuming you're using 802.11g) that shows the least activity (with your AP powered off) and interference.

There is *no way*, given proper setup, that a consumer-grade AP will outperform the Cisco APs (any of them) ... none, zero, zip, nada... the specs on the Cisco radios are among the best in the industry, and certainly well-ahead of SOHO units.

You should also verify that "Diversity" was enabled on the Cisco AP, it's very important, especially in "hard" environments with a lot of multipath.

At the frequencies that these APs are operating, it only takes movement of a couple cm to go from a really crappy signal to a really good one (signal quality is more important than signal strength).

What versions of hardware, firmware, and client software were you using?

Let us know ...

Good Luck



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