Arch Linux

XJDHDR

Member

Registered: 2015-06-14

Posts: 6

[SOLVED] Hostapd: Reduce signal strength?

Greetings

I recently got an Odroid which I installed Arch Linux onto. One of the things I wanted to do with it was to create a WiFi access point.

When I got it working, I noticed that the strength of the signal being put out is pretty high, to the point where the Odroid is currently putting out a stronger signal than my router which the Odroid will soon replace.

Is there an option in Hostapd's configuration file or elsewhere that would allow me to tone down the WiFi output? I tried searching the Arch Linux wiki, this forum and the internet but didn't see anything that helps me. Help will be greatly appreciated.

Kind regards

Last edited by XJDHDR (2015-08-26 14:42:01)

DarkCerberus

Banned

From: Holsworthy, Devon

Registered: 2011-12-31

Posts: 252

Re: [SOLVED] Hostapd: Reduce signal strength?

I've came across this while google searching http://www.datv-express.com/uploads/Use … raft04.pdf  - is this any helpful?

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XJDHDR

Member

Registered: 2015-06-14

Posts: 6

Re: [SOLVED] Hostapd: Reduce signal strength?

Thank you for the assistance but unfortunately, that guide doesn't appear to have helped. It looks like a guide for an expansion board for an Odroid U3 that adds cable TV capabilities.

My situation is that I have the Odroid XU3 Lite which I have plugged a USB WiFi adapter to - the EDUP EP-MS1532 (link).

In case anyone is confused or anything, I am not asking for instructions to get a WiFi hotspot setup or troubleshooting tips for this WiFi adapter; I have already created the WiFI hotspot using Hostapd and have had my BlackBerry Z30 connected to it the whole day. It works exactly the way a hotspot should behave.

What I want to do is reduce the WiFi signal strength to something less than it currently is and I haven't managed to find any instructions on how to do this with Hostapd.

Last edited by XJDHDR (2015-06-15 21:58:25)

Tarqi

Member

From: Ixtlan

Registered: 2012-11-27

Posts: 179

Website

Re: [SOLVED] Hostapd: Reduce signal strength?

1) Setup crda if not already done. Don't forget to set the correspondig country in hostapd.conf.
2) Check the module for possible options.

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qinohe

Member

From: Netherlands

Registered: 2012-06-20

Posts: 1,498

Re: [SOLVED] Hostapd: Reduce signal strength?

or elsewhere that would allow me to tone down the WiFi output?

If I understand you correct, use something like:

#iwconfig wlan0 txpower 2

see man iwconfig

progandy

Member

Registered: 2012-05-17

Posts: 5,280

Re: [SOLVED] Hostapd: Reduce signal strength?

AFAIK, iwconfig is deperacted just like ipconfig and we should use iw now.

$ iw
[...]
	dev <devname> set txpower <auto|fixed|limit> [<tx power in mBm>]
		Specify transmit power level and setting type.

	phy <phyname> set txpower <auto|fixed|limit> [<tx power in mBm>]
		Specify transmit power level and setting type.
[...]

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qinohe

Member

From: Netherlands

Registered: 2012-06-20

Posts: 1,498

Re: [SOLVED] Hostapd: Reduce signal strength?

AFAIK, iwconfig is deperacted just like ipconfig and we should use iw now.
......

Thanks progandy, for making it up to date

XJDHDR

Member

Registered: 2015-06-14

Posts: 6

Re: [SOLVED] Hostapd: Reduce signal strength?

Thanks for the help everyone.

@Tarqi
I tried but couldn't find any concrete information about crda and how to use it. The best I managed was this. I have set up crda to use the correct regulatory domain (South Africa, in my case) but I'm not sure what else I need to do.

@Progandy
Your advice seems to be working (working meaning didn't crash and burn with errors). I used this command:

$ sudo iw dev wlan-ap set txpower limit 100

which I'm guessing limits the transmission power to 100 mBm. This is the lowest I can go before I start getting "Operation not supported" errors.

One more question: How would I make this change permanent? I thought of putting the above command in a "ExecUpPost=" inside a Netctl profile but the problem with that is that Hostapd is what is starting the WiFi adapter, rather than Netctl.

Tarqi

Member

From: Ixtlan

Registered: 2012-11-27

Posts: 179

Website

Re: [SOLVED] Hostapd: Reduce signal strength?

I have set up crda to use the correct regulatory domain (South Africa, in my case) but I'm not sure what else I need to do.

Set the country code in hostapd.conf to the same as in /etc/conf.d/wireless-regdom, so that the localized settings may limit the transmit power of the device.

One more question: How would I make this change permanent? I thought of putting the above command in a "ExecUpPost=" inside a Netctl profile but the problem with that is that Hostapd is what is starting the WiFi adapter, rather than Netctl.

Copy /usr/lib/systemd/system/hostapd.service to /etc/systemd/system/hostapd.service and add

ExecStartPost=-/usr/bin/iw dev wlan-ap set txpower limit 100

to the service section. Note the - , this is intended and prevents the service to fail if the command fails. See man systemd.service.

Edit: Formatting & Grammar

Last edited by Tarqi (2015-06-17 22:45:16)

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Knowing others is wisdom, knowing yourself is enlightenment. ~Lao Tse

XJDHDR

Member

Registered: 2015-06-14

Posts: 6

Re: [SOLVED] Hostapd: Reduce signal strength?

Set the country code in hostapd.conf to the same as in /etc/conf.d/wireless-regdom, so that the localized settings may limit the transmit power of the device.

I see now. So I had to perform Progandy's instructions in addition to yours.

I would say that my question has been fully answered now. Thank you to everyone who helped out. Much appreciated.