How to Test Your Wifi Signal Strength
There are easy ways to test your wifi signal strength on your wifi enabled devices. Virtually all devices provide some means to see the wireless signal strength your device is receiving. On smart phones and tablets you can download free Apps that show you signal strength by graphical and or numeric means. A good FREE choice for Android phones or tablets is Wifi Analyzer from the Play Store which shows a graphical and numeric view of signal strength. The App displays all nearby networks, signal strength and the wireless channels they are using. On a Windows PC, laptop or tablet try NetStumbler (netstumbler.com) or Vistumbler (vistumbler.net) for Windows machines which both show the same nearby network information.
Apple does not allow the use of Wi-Fi scanning Apps on iOS devices but there is a version of WiFI Analyzer available on jailbroken iPhones and iPads for a few pence. On iphones you can also use the hidden Field Test Mode App by entering a code *3001#12345#* in the phone App. Search (youtube.com) for videos on how to do this. The effect is to convert the normal signal bars display to a numeric value. The smaller the number the better the signal. Try it first by testing the signal one meter away from the router to see the signal level numbers.
Mac OSX computers like Mac Books have a system report panel where you can select your current Wifi settings and signal readings directly received from your wireless router. To find the system report click the apple icon on the top bar -> about this mac -> more info -> system report and select Wi Fi from the menu. This shows the current connected device, signal strength, selected channel and possible connection speed. An even quicker way is to click the Wifi Icon in the top bar while holding the “alt/option” key. The signal strength is shown as an “RSSI” number but it looks like this number is the same value expressed in dBm.
Often signal strength is measured in dBm which is a logarithmic scale where the numbers are expressed like -85 dBm or -48 dBm (decibels with respect to 1 milliwatt). The numbers you will encounter will always be negative and a signal between -30 dBm and -70 dBm would be considered good. The smaller the number the better. A signal strength of -47 dBm is twice as strong as a signal of -50 dBm for example and a signal of -53 dBm would be one quarter as strong as a signal of -47 dBm. Every 3 dBm change in signal level doubles the signal strength if the number gets smaller or half’s it if the number gets bigger ignoring the sign of the number.
Even if the measured signal is low like anything from -70 dBm to -90 dBm it may still be possible to use the wifi signal. Your Wifi system speed is designed to get slower as the signal level gets smaller. This is to compensate for the expected error rate when signal levels are close to the radio noise and interference levels present in the wireless channel being used. For very noisy channels don’t expect to have any practical wifi use when your measured signal is -90 dBm. The greater the difference between your measured signal and the noise floor level the faster your wireless connection will be.
Remember also that the maximum wireless speeds quoted for your wireless network is not a real world useable speed. Expect that your maximum real useable speed will be around half this value due to signal encoding, protocol overhead, noise, contention and channel sharing factors.
So if you have a Wireless G network with a theoretical maximum speed of 54 Mb/s expect a useable data speed of 25 Mb/s. If your network speed is basic Wireless N with a maximum 150 Mb/s expect 72 Mb/s useable data rates in practice. But it all depends on the measured signal level in relation to the noise level.