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I have a wireless router with HostAPd running on Ubuntu. Now, with all the discussions about unhealthy EMF (electro-magnetic fields), I would be very interested to know, how I could configure my WiFi router to create as little EMF as possible? (There's already at least one commercial product, which goes into that direction: JRSeco. They do that by reducing the pulse rate and stop sending anything when in stand by.)

  • What configuration switch in HostAPd could help in achieving this goal?
  • Are there any WiFi cards, which together with HostAPd, do Beam Forming?
  • There's a function that is called "tx auto", which is supposed, if I got that right, to adapt the signal strength to the signal quality. But I am not really sure, if it has any effect on my site. Are there WiFi cards, which implement this functionality correctly?
  • What about aiting for a new WiFi standard?
  • What WiFi card capabilities do help in achieving this goal? (My cards have [RXLDPC][HT40-][HT40+][SHORT-GI-20][SHORT-GI-40][TX-STBC][RX-STBC1][MAX-AMSDU-3839][DSSS_CCK-40] and [LDPC][HT40-][HT40+][SHORT-GI-20][SHORT-GI-40][TX-STBC][RX-STBC1][MAX-AMSDU-7935][DSSS_CCK-40]
  • Any other ideas, URLs,…?

Thanks

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    Well, I've been asking about configuration of those cards with HostAPd. – moetteli Mar 2 at 16:40
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    Do you have a lightbulb? How many watts is it? Well, your WiFi router only puts out 1/10 of a watt, using frequencies which are far less energetic than light. If you're still concerned, switch to wired Ethernet which keeps all the signal in the cables and does not emit anything. – K7AAY Mar 2 at 16:50
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    @mchid That description should remain on Skeptics.SE as that discussion isn't necessarily needed here. (Also was not necessarily relevant to the point of my statement that this isn't necessarily an Ubuntu question but a hardware design question) – Thomas Ward Mar 2 at 19:49
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If you are running Ubuntu, you can decrease your tx level using iwconfig.

First, run the following command to list your available devices:

iwconfig

The wireless device in the following example is wlp2s0 and your broadcast device name may be different so use the wireless device from your list.

sudo iwconfig wlp2s0 txpower 0

The command will set the txpower to 0 dBm which is equal to 1 mW. The default is usually set to 20 dBm. I have found that my devices usually perform well at less than 20 dBm. You can change the txpower value as needed. Here is the formula to calculate mW from dBm for reference:

mW = 10dBm/10

  • 20 = 100 mW
  • 10 = 10 mW
  • 5 = 3 mW
  • 0 = 1 mW

Next, if there is not much interference and you are not using devices over a large range, you can also reduce the "retry" value but this may cause a more noticeable decline in performance. I believe the default retry value is usually "short 7". Here is an example:

sudo iwconfig wlp2s0 retry short 5

Use the iwconfig command to verify your settings.

Additionally, you can use the power saving "Power Management" feature as well. Again, this feature sometimes negatively affects performance so you will need to test it out.

sudo iwconfig wlp2s0 power on

and use the power off option instead to disable power management.

These iwconfig commands are not persistent across reboots so you will need to run them again after you reboot or as a startup script or something like that. I've never used these settings with HostAPd so settings like Power Management and retry may perform differently for your setup.


Finally, there are some basic HostAPd examples for your configuration file at the Ubuntu WifiDocs WirelessAccessPoint help page. If your setup is currently working, these basic examples are not be needed.

However, an extremely detailed example config file can be found here. Of course, you will need to uncomment any lines you want to use and you can just copy and paste these lines into your /etc/hostapd/hostapd.conf configuration file. To generate a copy of the detailed example file in your home directory (for future reference), run the following command:

zcat /usr/share/doc/hostapd/examples/hostapd.conf.gz | tee ~/hostapd.conf

The detailed example file does mention beamforming (beamformer and beamformee) and there many other settings that will help you achieve your goal (Station inactivity limit" amongst many others). However, your ability to use these features will be based on the capabilities of your hardware.

See also:

hostapd Ubuntu manpage

hostapd_cli Ubuntu manpage

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