Quickly I came across a well hidden Apple gem called Wireless Diagnostics Tool or Diagnose für drahtlose Umgebungen on my German OS X Mavericks.
Where to Find the Application
The application should be installed on every current Mac out there and you just have to use it. It is well hidden from normal users and the easiest way I found to start it, is to type “diag” into Spotlight (⌘-Space) and you should see an application with the above icon.
The path to the Wireless Diagnostics Tool is
on my System (OS X Mavericks, 10.9.1).
How to Verify Signal Quality in Wi-Fi Networks
First you should have a look at all available Wi-Fi networks in your neighborhood and check out if you see any conflicting or crowded channels. If this is the case it might be a good idea to force your Wi-Fi router to another channel. Unfortunately I can not provide instructions on how to do this since this is different on each kind of router model out there.
After you got an overview over the used channels in your neighborhood, click on the Performance button to see how your network performs at the moment.
The Signal-to-Noise Ratio (SNR) directly shows the quality of the Wi-Fi signal. For this graph I found the following guidline quite useful, which probably applies to the three or four bars on the mobile phones to represent Wi-Fi signal quality.
SNR Guideline 40+dB = Excellent signal 25dB to 40dB = Very good signal 15dB to 25dB = Low signal 10dB to 15dB = Very low signal 5dB to 10dB = Little or no signal Source: Optimal Base Station Placement by Tesserax
In the signal graph, you get the two base values of your Wi-Fi connection, the Received Signal Strength Indication (RSSI) and noise. The SNR is simply the difference between RSSI and noise.
When working with those values you have to keep in mind that signal quality and noise are both negative values and the SNR is a positive value, which originates from the calulation
-20 - -85 = +65
. So in general, the bigger further apart RSSI and noise are, the better is your signal quality.