5 Replies Latest reply: Jun 18, 2011 10:03 AM by Bob Timmons
joe619 Level 1 Level 1 (0 points)

I bought a refurbished Airport Express from the apple website last week to extend my wireless network to the other side of my house from my Airport Extreme. I set it all up, and updated both airports to the latest software update, then restarted them.  Everything seemed to work fine. 


But a day or so later, I noticed weak signal on the other side of my house again.  airport express was on and had a green light, but when I checked it with the airport utility, it had no clients associated with it.  Even if I was standing right next to it, and turned my iphone on, it would associate to the weaker airport across my house and not the airport express right in front of me.  The laptop on the other side of my house has a VERY weak signal, just like before I installed the airport express.  I unplugged the airport express and plugged it back in, then my clients were able to associate to it again. 


Please correct me if I'm wrong, but when you extend your wireless network, aren't your clients are supposed to connect to the strongest signal.  So if one of my devices is less than a foot away, it should connect to that airport express, not the one all the way across the house with the much weaker signal. 


I'm just wondering if this is a known issue?  Or maybe I got a defective refurbished unit?  Either way, I bought it for the most part to extend my network.  If it's not going to be capable of that, I need to look into returning it.  I don't want to have to reboot the airport express every day or so to make it function properly. 

  • Bob Timmons Level 10 Level 10 (91,870 points)

    Do  you have the AirPort Express located at a point that is about 1/2 the distance from the AirPort Extreme and the general area that needs more wireless coverage?


    The Express can only "extend" or "repeat" what it receives and make that bandwidth go further. It does not "boost" the signal. So, if it's located too far from the AirPort Extreme, it is not receiving enough signal to extend effectively.


    Anything you can do to minimize obstructions....walls, ceilings, etc in the signal path will also help the strength and bandwidth of your wireless signal. Even a typical wall in a home of sheet rock and 2 x 4s will on average absorb 15-20% of the signal, so if you have more than a few walls in the signal path, you are losing a great deal of signal.


    If there are too many obstructions in the signal path, you may need to look at another Ethernet method to "extend" the wireless signal to provide better coverage to the remote areas.

  • joe619 Level 1 Level 1 (0 points)

    Yes, the airport express is about half way, and yes, it gets a decent signal from the main airport extreme (Signal -59, noise -84, rate 115)  Like I said, it works fine, for a bit, then all of the sudden NOTHING could associate with it. 


    Even if the airport express was too far from the main base station, devices should STILL be able to associate with it, just maybe not pass any traffic.  If I'm connected using the airport utility, and watch, NOTHING is connected to it. 

  • Bob Timmons Level 10 Level 10 (91,870 points)

    A Signal of -59 dBm minus noise of -84 dBm would yield an SNR of 25 dBm, which is right on the edge as far as a decent signal would be concerned. 30-35 would be desirable, if possible.


    If things seem to work fine...then all of sudden go south, there are several possibilities for this:


    1) The Express is picking up some form of intermittent wireless interference from another cordless phone, wireless network, or wireless camera/security system. Any of thes devices could be at the neighbors, for example like a situation that I've experienced in the past when I discovered that my neighbor...across the street....could knock out my "extending" Express if he was in his front yard talking on his cordless phone.


    2) The Express is overheating internally and this is causing a problem with an electronic component that causes a loss of connection with main base station.


    Even if the airport express was too far from the main base station, devices should STILL be able to associate with it, just maybe not pass any traffic.

    I don't think this is correct. In 3 tests here when I purposely located an Express well beyond the point where it could not pick up a signal from the main base station, devices would not associate with the Express. How could they if the Express was not "extending" a signal that the devices could pick up?

  • joe619 Level 1 Level 1 (0 points)



    As far as the numbers I gave, I would NOT say it "is right on the edge as far as a decent signal would be concerned".  In fact, I would say those numbers are fairly decent for a wifi network. 


    Here is corroboration: 


    http://www.enterprisenetworkingplanet.com/netsp/article.php/3747656/Wi-Fi-Define -Minimum-SNR-Values-for-Signal-Coverage.htm



    • > 40dB SNR = Excellent signal (5 bars); always associated; lightning fast.
    • 25dB to 40dB SNR = Very good signal (3 - 4 bars); always associated; very fast.
    • 15dB to 25dB SNR = Low signal (2 bars); always associated; usually fast.
    • 10dB - 15dB SNR = Very low signal (1 bar); mostly associated; mostly slow.
    • 5dB to 10dB SNR = No signal; not associated; no go.

    These values seem consistent with testing we've done in the past, as well as what some of the vendors publish."

    As well as the fact that as soon as I reboot the airport express, everything starts working as it should. 

    I have not tested my hypothesis with devices still being able to associate with an airport express that is too far away from the base station.  But I believe it is doing WDS with the main base station.  If that is the case, devices should STILL be able to associate with it, even when it is too far away.  That is NOT to say they will have internet access, but will at least be able to associate with the airport express.  I will try to test this later today...

  • Bob Timmons Level 10 Level 10 (91,870 points)

    I'm very familier with the SNR scale that you posted and it reinforces exactly what I said....25 dBm SNR is right on the edge.


    Are you really interpreting the entire 25-40 range to be equal signal quality?  25 is the same as 40? Not in my book.