Mac OS X Wireless Signal Strength in Snow Leopard

The AirPort item in the menu bar now includes signal strength for all available wireless networks, so you can see which access point has the best signal before selecting it. Four signal bars appear in the AirPort status icon in the menu bar. The more bars that are black, the higher the signal quality. The bars do not indicate the connection rate, as this will vary according to your environment. [source]

While I like the simplicity of the four levels of signal strength above I sometimes need signal strength in dBm. dBm is a more granular way of describing the wireless signal strength.

dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. Compare dBW, which is referenced to one watt (1000 mW). In the more granular information about the signal strength. [wikipedia]

Wireless Signal Strength Using the Snow Leopard Menu Bar

Clicking the option key and the signal strength menu icon will display detailed information about the currently connected wireless network.

PHY Mode – is the type of 802.11 WiFi network (802.11 a/b/g/n)
BSSID – is the MAC address of the access point
Channel – current 802.11 channel
Security – authentication and encryption type
RSSI – received signal strength indicator, aka the signal signal strength in dBm. The closer the number to 0 the stronger the signal.
Transmit Rate – the data rate of the current connection

Airport Signal Strength in dBm Using “About This Mac”

Wireless signal strength is also available using the About This Mac menu bar option and navigating to Network > Airport section.

RSSI Signal Strength Airport Command Line Utility

The airport utility is located at location below.

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

Will provide information about the current wireless connection.

$ airport -I
     agrCtlRSSI: -64
     agrExtRSSI: 0
    agrCtlNoise: -91
    agrExtNoise: 0
          state: running
        op mode: station
     lastTxRate: 48
        maxRate: 54
lastAssocStatus: 0
    802.11 auth: open
      link auth: wpa-psk
          BSSID: 0:b:55:6:6f:2f
           SSID: SSID
            MCS: -1
        channel: 1

Wireless Signal Strength Using Graphical Tools

WiFi Scanner is a free 802.11 wireless scanner and connection manager for Mac OS X 10.6 Snow Leopard or later. It leverages the the newest CoreWLAN API in Snow Leopard. This will detect access points and clients in ad-hoc mode if the SSID is being broadcasted. It can be used for wireless site surveys, wireless discovery, and to connect to wifi networks. The tool reports signal strength in dBm and shows access point BSSID/MAC addresses.

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Filed under: WLAN Design, WLAN Site Survey, WLAN Tools