WiFi Antenna Broken

Installing and Using OpenWrt Network and Wireless Configuration
1

Hello,

I broke a coaxial connector (CH0 2.4GHz) on the Xiaomi Mi Router 3G board...
There are still 3 functionnal antennas :
CH1 for 2.4GHz
CH0 and CH1 for 5GHz
I have no problem with 5GHz but the 2.4GHz is not good at all.
Is it possible to disable CH0 for 2.4GHz to have better performance ?

Thanks

EDIT :
I tried to modify, is it ok ?

config wifi-device 'radio0'
        option type 'mac80211'
        option hwmode '11g'
        option path 'pci0000:00/0000:00:00.0/0000:01:00.0'
        option htmode 'HT20'
        option legacy_rates '1'
        option channel '11'
        option country 'FR'
        option distance '15'
        option diversity '0'
        option rxantenna '2'
        option txantenna '2'
1 Like
2

That looks like a reasonable approach. If you’ve got connectivity and iw is reporting 1x1 connection, you’ve probably done it.

3

Can you give me the iw command please ?

4

I don't know your device names, they are probably wlan1-1 or the like, but on one of my devices

jeff@office:~$ iw dev ap2_bbb station dump
Station 7c:d1:c3:aa:aa:aa (on ap2_bbb)
	inactive time:	52740 ms
	rx bytes:	7514703
	rx packets:	38731
	tx bytes:	7737485
	tx packets:	30081
	tx retries:	110
	tx failed:	555
	rx drop misc:	34
	signal:  	-71 [-71, -88, -95, -95] dBm
	signal avg:	-70 [-70, -85, -95, -95] dBm
	tx bitrate:	65.0 MBit/s MCS 7
	rx bitrate:	39.0 MBit/s MCS 4
	rx duration:	7655972 us
	last ack signal:-69 dBm
	authorized:	yes
	authenticated:	yes
	associated:	yes
	preamble:	short
	WMM/WME:	yes
	MFP:		no
	TDLS peer:	no
	DTIM period:	2
	beacon interval:100
	short preamble:	yes
	short slot time:yes
	connected time:	586927 seconds
Station 18:b4:30:bb:bb:bb (on ap2_bbb)
	inactive time:	400 ms
	rx bytes:	13933451
[...]

Looking at

	signal:  	-71 [-71, -88, -95, -95] dBm
	signal avg:	-70 [-70, -85, -95, -95] dBm
	tx bitrate:	65.0 MBit/s MCS 7
	rx bitrate:	39.0 MBit/s MCS 4

I see two antennas receiving signal.

At least for 802.11n and "HT" modes, MCS 0-7 are single-stream modulations. It doesn't look like VHT is as easy to tell the difference between single- and multi-stream modulation from the MCS index alone.

See also https://en.wikipedia.org/wiki/IEEE_802.11n-2009

5

Here is the result :

Station 28:6c:07:89:24:4e (on wlan0)
        inactive time:  2890 ms
        rx bytes:       174752
        rx packets:     1030
        tx bytes:       54007
        tx packets:     517
        tx retries:     279
        tx failed:      4
        rx drop misc:   0
        signal:         -43 [-84, -43] dBm
        signal avg:     -42 [-83, -42] dBm
        tx bitrate:     13.0 MBit/s MCS 1
        rx bitrate:     19.5 MBit/s MCS 2
        expected throughput:    8.879Mbps
        authorized:     yes
        authenticated:  yes
        associated:     yes
        preamble:       short
        WMM/WME:        yes
        MFP:            no
        TDLS peer:      no
        DTIM period:    2
        beacon interval:100
        short preamble: yes
        short slot time:yes
        connected time: 3550 seconds

Is it ok for you ?

6

I would have expected to see a "zero" for the first antenna there ("-95" or some other consistent number). I haven't looked into to the bitmaps for antennas in a while. You might want to look into https://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf and what is generated on your machine in /tmp/run/

You also might try "poking at it" with iw -- from the help it provides

	phy <phyname> set antenna <bitmap> | all | <tx bitmap> <rx bitmap>
		Set a bitmap of allowed antennas to use for TX and RX.
		The driver may reject antenna configurations it cannot support.

Also, the values could be listed with something like

iw phy phy1 info | head -n20
Wiphy phy1
	max # scan SSIDs: 16
	max scan IEs length: 195 bytes
	max # sched scan SSIDs: 0
	max # match sets: 0
	max # scan plans: 1
	max scan plan interval: -1
	max scan plan iterations: 0
	Retry short limit: 7
	Retry long limit: 4
	Coverage class: 0 (up to 0m)
	Device supports AP-side u-APSD.
	Available Antennas: TX 0x3 RX 0x3
	Configured Antennas: TX 0x3 RX 0x3
	Supported interface modes:
		 * IBSS
		 * managed
		 * AP
		 * monitor
		 * mesh point

When I try to set the antenna on my device, it fails -- you might want to check your logs.

jeff@office:~$ sudo iw phy phy1 set antenna 0x2
command failed: Not supported (-95)
1 Like
7

You broke the connector of the cable or on the main board?
How good are you at soldering? Or is this no reasonable approach for you?

Edit: Now i read board :smiley:
So are the soldering pads on the board ok?

8

70793923_2375479012564916_1789274725449465856_o
70793923_2375479012564916_1789274725449465856_o.jpg884×1010 126 KB

Even scratching I can not find the track...

EDIT : I have a USB Wifi key TP-LINK TL-WN823N V2, can I use it ?
If not, someone can advise me for an USB key ? Thanks

1 Like
9

The copper live trace is right there below where the pad ripped off. Taking the board out of the frame will show it better. That's very fixable by someone with experience at such things.

WN823N uses a Realtek chip which tends to be not well supported. Any USB adapter is limited by the bus bandwidth and latency so it won't work as well as a chip with an internal or PCI connection.

1 Like
10

you should patch driver to force it to 1x1 mode as userspace tools generally won't support it. since you damaged main chain that might be a bit tricky. or you can keep scratching until you break something else