dBm wireless signal strength

dBm signal strength of my wifi connection

You usually check the signal strength of your wireless connection on your phone or laptop by looking at how many bars or waves are highlighted in the GUI. This is a good approximation to know if your signal is weak or strong. However, if you need to measure the strength of your connection, for example at different locations in your home, then you need to know the actual metric.

  • dBm (decibel-milliwatts) is the commonly used metric to measure wifi signal strength or power.

  • If you check the technical specifications of your wireless router, you should find that it transmits at less than -20dBm. Note that this a negative value. So, a value that looks bigger, like -50dBm means a weaker signal.

  • If you put your phone or laptop right beside your wireless router, you should find the strength to be between -20dBm and -30dBm. This gives you an idea of the max strength you can realistically achieve with your home setup.

  • According to this page, you will need at least -70dBm for browsing and -80dBm is the farthest signal strength thats practically usable. At -90dBm the signal is basically indistinguishable from noise.

  • To view the dBm signal strength of your wifi connection on your Android device, I highly recommend the open-source WiFiAnalyzer app. You can see the dBm signal strength of your and all other wifi connections from your phone with this app.

  • To view the dBm signal strength of your wifi connection on your Linux computer, just type iwconfig and note the Signal level field in the output:

$ iwconfig
wlp4s0    IEEE 802.11  ESSID:"my_wifi_network"  
          Mode:Managed  Frequency:2.427 GHz  Access Point: xx:xx:xx:xx:xx:xx   
          Bit Rate=65 Mb/s   Tx-Power=22 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:on
          Link Quality=42/70  Signal level=-68 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:96   Missed beacon:0

You can move around your laptop to different locations in your home and note the dBm values there. This can be useful if you want to decide on the optimal placement of your wifi router or if you are planning to get a wifi extender for your home.

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WiFi Radar

20150214_wifi_radar

WiFi Radar is a small GUI utility that can be used to scan the wireless networks in your neighborhood. It shows the available networks, their strength and the channel they are on. Using this information you can decide which channel you would like your wireless router to use. It can also be used to manage connections, though I prefer to use Ubuntu’s default tool to do that.

It can be installed easily:

$ sudo apt install wifi-radar

Tried with: WiFi Radar 2.0.s08 and Ubuntu 14.04

The strange case of the disconnecting wireless router

Problem

At 2PM today, I started noticing problems with my home wireless network. All the devices connected wirelessly to the wireless router started getting disconnected and reconnected repeatedly. Even when connected for the brief period, the Internet speed was an order of magnitude less than normal.

The wireless router is a D-Link DCM-604 cable wireless modem-router provided by Starhub. There were two Android smartphones, an Aftershock XG15 V2 notebook and a Macbook Air 2013 connected to the network which experienced these problems.

Solution

I thought that this was a problem with the wireless router. But, resetting the wireless router to factory settings did not help. I spent a lot of time going through the settings of the router, hoping that something had gone wrong with one of them. However, connecting to the router using an Ethernet cable worked fine.

On mulling over this problem and its symptoms, I had no choice but to settle on a crazy conclusion: one of the wireless devices was causing this problem. I do not know how a wireless client could be continuously messing with the wireless router, to the point that its affecting the entire wireless network. But, I decided to test this.

To do that, I started by powering off the connected devices one by one, restarting the wireless router each time and checking the status of the wireless network. And soon I hit pay dirt: the Aftershock XG15 V2!

This notebook was using a Qualcomm Atheros AR9462 wireless network adapter. I was running Ubuntu 14.04 with kernel 3.13.0.40-generic on it. I do not know whether the hardware or the driver was causing this problem and how. Turning off the wireless from Ubuntu tray icon did nothing. But on restarting the device and then restarting the wireless router, peace was restored. All the devices connected and worked fine!

Tried with: Aftershock XF15 V2 notebook, Qualcomm Atheros AR9462 wireless network adapter, Ubuntu 14.04 and D-Link DCM-604 wireless router

How to add USB wireless adapter to Raspbmc

I hate wires. So, I was happy to remove the ethernet cable from my Raspbmc setup and replace it with a USB wireless adapter. The steps are pretty easy:

  1. Get a USB wireless adapter. These are very cheap. I bought a DX Original USB wireless adapter, since I had read that it works out of the box with Raspbmc. Plug in the wifi adapter to your Raspbmc.

  2. Connect a wired or wireless mouse or remote to the Raspbmc. Use it for the configuration steps.

  3. Reboot the Raspbmc. This is needed sometimes for the mouse to be detected.

  4. Go to Programs > Raspbmc settings. In the Network Configuration tab change the Network Mode to Wireless.

  5. Configure the rest of the settings. The default is DHCP. If you want to use a static IP address, provide the necessary details.

  6. The scan for wireless networks did not work, it showed up empty. So, I manually entered the Wifi SSID (name of your wireless network), Wifi Security mode and the Wifi Key (wireless password). Click Update Now and OK.

  7. Your wireless adapter should be able to connect to your home network now. If not, reboot the Raspbmc.

  8. Unplug the Ethernet cable and enjoy your Raspbmc πŸ™‚

How to create wireless hotspot on Windows 8

There are some situations where you may have to create a wireless hotspot from your Windows 8 notebook. For example, you have only a wired LAN connection to the Internet, but have wireless-only devices like smartphones or tablets. In these situations, your Windows 8 notebook can be configured to act as a wireless router offering wireless access to internet to your other gadgets.

This can be done on Windows 8 in a few steps:

  • Open a command prompt with Administrator privileges. Use this command prompt for all the commands given below.

  • Check if the wireless adapter has support for Hosted Network. This is needed to make it work as a wireless hotspot. This can be checked by using this command:

netsh show wlan drivers

This prints out all the properties of the wireless adapters on your notebook. Look for the property named Hosted network supported and it should be say Yes. If it says No, you are out of luck 😦

  • Create a hosted network with a name and a key. Lets assume the network is named foobarwifi and key is foobarkey. The command to create such a network is:
netsh wlan set hostednetwork mode=allow ssid=foobarwifi key=foobarkey
  • Start this hosted network using this command:
netsh wlan start hostednetwork
  • Next, we need to link the network connection that has internet access to this wireless hosted network. To do this, open the Network and Sharing Center and go to Change adapter settings. You should be able to see the connection that has internet access. You will also see a Local Area Connection with the name foobarwifi. It will have a * (asterisk) in its name.

  • Right-click on the connection with internet access and choose Properties. Switch to the Sharing tab and enable the option: Allow other network users to connect through this computers internet connection. In the dropdown, pick the Local Area Connection that is foobarwifi.

  • That is it! Your Windows 8 notebook is now available as a wireless hotspot named foobarwifi to which other devices can connect wirelessly using the key foobarkey.

  • This wireless hotspot is temporary and is removed when Windows is rebooted. If you need this hotspot frequently, then create a .bat file on the desktop with the above two command lines in it. Shift + right click on the file and choose Run as Administrator whenever you want the wifi hotspot to be created.

Tried with: Windows 8 x64

How to remove wireless network profile in Windows 8

Windows 8 just does not provide the GUI to perform certain operations. For example, you cannot remove the network profile for a wireless network. This cannot be done with the Charms Bar nor using the Network and Sharing Center.

This is an important operation because it is all too easy to click and join many networks. And over time you may want to change the settings or just remove some of those wireless network profiles. Thankfully, you can still do this from the command prompt.

To list all the wireless network profiles:

C:\> netsh wlan show profiles

To remove a wireless network profile named foobar:

C:\> netsh wlan delete profile name="foobar"

Tried with: Windows 8 x64

How to SSH wirelessly to your Nook Color running CyanogenMod 10

SSH to Nook Color running CyanogenMod 10
SSH to Nook Color running CyanogenMod 10

The Nook Color can be easily made to run CyanogenMod 10. If such a Nook Color is connected to the same home (wireless) network as your computer, then it is pretty easy to SSH to it wirelessly.

  1. Make sure your Nook Color running CM 10 is powered on and connected to the home network.
  2. Note down the IP address assigned to your Nook Color. Since the IP address given by DHCP varies, it is convenient to assign a static IP address to your Nook Color.
  3. Install a SSH server on the Nook Color. I installed DropBear Server II from the Google Play Store.
  4. Start the DropBear Server II app. Choose Install. You will be asked to provide it superuser privileges.
  5. Start the SSH server by choosing Start in DropBear Server II.
  6. The password for root user can be found in the Settings section of DropBear Server II. Change it to anything you want.
  7. On your computer, ping the IP address of the Nook Color to make sure it is reachable over wireless. If you cannot ping it, you have some networking problem.
  8. If you can ping your Nook Color and its SSH server is running, then SSH to it using PuTTY. Provide the IP address of Nook Color and use root as user and password set in DropBear Server II as the password.

Happy hacking! πŸ™‚

Tried with: Nook Color 8 GB, CyanogenModΒ 10-20121228-NIGHTLY-encore and DropBear Server II 1.5.4

Wireless card not working on Dell Vostro 3300

Problem

I installed Ubuntu on a Dell Vostro 3300 notebook. (Note that I faced the exact same problem with a Dell Inspiron 1320 and solution is same as below.) After installation, I find that wireless is not working. Even the wireless notification light above the keyboard is not turned on.

I used lspci to check if the wireless card is detected:

$ sudo lspci -v

12:00.0 Network controller: Broadcom Corporation BCM4312 802.11b/g LP-PHY (rev 01)
    Subsystem: Dell Wireless 1397 WLAN Mini-Card
    Flags: bus master, fast devsel, latency 0, IRQ 17
    Memory at fbb00000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: [40] Power Management version 3
    Capabilities: [58] Vendor Specific Information: Len=78 <?>
    Capabilities: [e8] MSI: Enable- Count=1/1 Maskable- 64bit+
    Capabilities: [d0] Express Endpoint, MSI 00
    Capabilities: [100] Advanced Error Reporting
    Capabilities: [13c] Virtual Channel
    Capabilities: [160] Device Serial Number xx-xx-xx-xx-xx-xx-xx-xx
    Capabilities: [16c] Power Budgeting <?>
    Kernel driver in use: b43-pci-bridge

I find that Broadcom BCM4312 chip in the Dell Wireless 1397 wireless card is detected and a b43-pci-bridge driver has been installed. This is not a WLAN driver.

Solution

Broadcom chips need the driver provided by Broadcom. This needs to be installed for the card to work.

Ubuntu 14.04

  • Connect to the internet using a LAN cable.

  • Install the Broadcom driver:

$ sudo apt-get update
$ sudo apt-get --reinstall install bcmwl-kernel-source
  • Restart Ubuntu.

My wireless card worked after this. The wireless notification light above the keyboard too was lit up.

I checked lspci again and found the correct driver now installed:

$ sudo lspci -v

12:00.0 Network controller: Broadcom Corporation BCM4312 802.11b/g LP-PHY (rev 01)
    Subsystem: Dell Wireless 1397 WLAN Mini-Card
    Flags: bus master, fast devsel, latency 0, IRQ 17
    Memory at fbb00000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: [40] Power Management version 3
    Capabilities: [58] Vendor Specific Information: Len=78 <?>
    Capabilities: [e8] MSI: Enable- Count=1/1 Maskable- 64bit+
    Capabilities: [d0] Express Endpoint, MSI 00
    Capabilities: [100] Advanced Error Reporting
    Capabilities: [13c] Virtual Channel
    Capabilities: [160] Device Serial Number xx-xx-xx-xx-xx-xx-xx-xx
    Capabilities: [16c] Power Budgeting <?>
    Kernel driver in use: wl

Ubuntu 10.04

To enable wireless, choose System β†’ Administration β†’ Hardware Drivers. The system will now search for required proprietary drivers. In the list it presents, choose the Broadcom STA Wireless Driver. After it is installed, reboot and your wireless card should now work.

Connectify: Windows 7 and Ubuntu Laptops

Connectify is a useful application that turns a Windows 7 laptop into a wireless hotspot. Other laptops can then connect to it wirelessly and access the Internet through it. Instead of buying a wireless router, I have connected a Windows 7 laptop to the Internet and run Connectify on it. The other Ubuntu laptop at home accesses the Internet by connecting wirelessly to the network that Connectify creates. It all works like a charm with minimum tweaking!

The only problem I faced was that DNS was very flaky on the Ubuntu laptop. So, I configured it to use OpenDNS (instructions here) and everything works fine now! πŸ™‚