Garrett Bryant
Level 1 (79 points)
Mac OS X

Q: Help me with an interference issue?

Here is my network:

Motorola modem -> Airport Extreme (with external HD) -> 2 MacBooks, 2 iPhones, AppleTV, Sony Bluray.

 

I live in a suburban neighborhood with few homes near-by, with only three other wifi networks showing up besides my own. My modem and Extreme are in the den in the back of my house. Everything is fine when in the den or back of the house, however when I get upstairs or on my front porch my internet dies. I still have ALL the bars on my Macbook's wifi display so signal strength and interference is not the issue.

 

I have run Apple's (deeply hidden) Wi-Fi Diagnostics app (found via: http://goo.gl/THkZU) and found the signal-to-noise ratio changes dramatically moving from den to front room to front porch. Here is a screen cap of the readout:

 

wifi.jpg

 

Far-right is in the back den, then kitchen, then front living room, then finally front porch is on the far-left.

 

How can I find out more information and remedy this problem?

MacBook, Mac OS X (10.7.2)

Posted on Mar 8, 2012 11:24 AM

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Garrett Bryant

Q: Help me with an interference issue?

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  • by Tesserax,

    Tesserax Tesserax Mar 8, 2012 12:17 PM in response to Garrett Bryant
    Level 9 (54,906 points)
    Wireless
    Mar 8, 2012 12:17 PM in response to Garrett Bryant

    Yes, that hidden tool is a good one to use. What you basically have is the means to calculate the Signal-to-Noise Ratio (SNR) which is a good indicator of signal quality.

     

    SNR (in dB) = Signal (in dBm) - Noise (in dBm)

     

    In addition to the Wi-Fi Diagnostics app, you can also find the Signal and Noises values using System Profiler on your Mac laptop.

     

    ref: Click on the Apple icon on the menu bar > About This Mac > More Info... > Contents > Network > AirPort > Interfaces > en1 > Current Network Information > Find your wireless network > Signal / Noise. In addition, you can find the Transmit Rate here as well.

     

    These values should be negative numbers. For example, mine currently read: -67 dBm / -95 dBm, with a transmit rate of 27 (Mbps). Plugging in these numbers yield: SNR = -67 - (-95) = 28. My Mac Mini is about four rooms away from my AEBS with about five walls between them. As you can see, the signal is still quite useable ... but the bandwidth is minimal, especially for streaming.

     

    The following is a guidline for SNR values:

     

    SNR Guideline

    • 40dB+ SNR = Excellent signal
    • 25dB to 40dB SNR = Very good signal
    • 15dB to 25dB SNR = Low signal
    • 10dB to 15dB SNR = Very low signal
    • 5dB to 10dB SNR = No signal

     

    What you will want to do (and have pretty much have already done) is to gather the Signal and Noise values at each point in the house where you would want to access the wireless network ... and then, calculate the SNR resultant. Anywhere where the SNR is 25+dB, you can expect decent wireless performance.

     

    To improve SNR at any particular location may require reconfiguring your wireless network into either an extended or roaming network and would require additional base stations to do so.