Wifi connection is weak and drops off - Quallcom Atheros AR9485 on Asus S400CA

[Matematik]

Wifi connection on my Asus S400 with Quallcom Atheros AR9485 wifi card is very weak. When I try to browse the web my wifi connection often drops off. On other laptops in my house I have full-strength connection, but this laptop is only showing 2 out of 5 bars. Sometimes the wifi icon shows that I'm connected, but pings don't go through and web pages are not accessible.

This problem was happening to me on Ubuntu 12.04, 14.04, and now 15.04. It became very troublesome when I switched from an old Netgear wireless router (which died) to DLink DIR-601.

Should I change wifi card or there's a problem with my config? Should I report it as a bug on Launchpad? Any suggestions on tackling this problem are very much appreciated!

I'm attaching dmesg and /var/log/syslog logs captured around the time when problem occurred

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When I have my wireless connection dropped I'm usually trying to bring it back up with the following script:

#!/bin/bash
set -x
sudo service network-manager stop
sudo rmmod -v ath9k
sudo modprobe -v ath9k
sudo service network-manager start

Here's some more system information

$ sudo iwlist wlan0 scan
wlan0 Scan completed :
Cell 01 - Address: 00:26:5A:F7:AC:EE
Channel:6
Frequency:2.437 GHz (Channel 6)
Quality=67/70 Signal level=-43 dBm
Encryption keyn
ESSID:"Kolobok"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=00000003ec8a287c
Extra: Last beacon: 8ms ago
IE: Unknown: 00074B6F6C6F626F6B
IE: Unknown: 010882848B968C129824
IE: Unknown: 030106
IE: Unknown: 0706555349010B1B
IE: Unknown: 200100
IE: Unknown: 2A0100
IE: Unknown: 3204B048606C
IE: Unknown: DD180050F2020101830003A4000027A4000042435E0062322F 00
IE: Unknown: DD1E00904C334C101BFF000000000000000000000000000000 00000000000000
IE: Unknown: 2D1A4C101BFF00000000000000000000000000000000000000 000000
IE: Unknown: DD1A00904C3406001B00000000000000000000000000000000 000000
IE: Unknown: 3D1606001B00000000000000000000000000000000000000
IE: Unknown: DD0900037F01010000FF7F
IE: Unknown: DD0A00037F04010002004000
IE: Unknown: DD9E0050F204104A0001101044000102103B00010310470010 0000000000001000000000265AF7ACEE10210006442D4C696E 6B1023000D442D4C696E6B20526F7574657210240007444952 2D363031104200046E6F6E651054000800060050F204000110 110016442D4C696E6B2053797374656D73204449522D363031 100800020086103C000103104900140024E260020001016000 00020001600100020001
IE: Unknown: DD050050F20500

$ sudo lshw -C network
*-network
description: Wireless interface
product: AR9485 Wireless Network Adapter
vendor: Qualcomm Atheros
physical id: 0
bus info: pci@0000:02:00.0
logical name: wlan0
version: 01
serial: dc:85:de:a2:2b:d6
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list rom ethernet physical wireless
configuration: broadcast=yes driver=ath9k driverversion=3.19.0-26-generic firmware=N/A ip=192.168.0.106 latency=0 link=yes multicast=yes wireless=IEEE 802.11bgn
resources: irq:17 memory:f7d00000-f7d7ffff memory:f7d80000-f7d8ffff
*-network
description: Ethernet interface
product: AR8161 Gigabit Ethernet
vendor: Qualcomm Atheros
physical id: 0
bus info: pci@0000:03:00.0
logical name: eth0
version: 10
serial: 50:46:5d:45:94:9c
capacity: 1Gbit/s
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi msix bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=alx latency=0 link=no multicast=yes port=twisted pair
resources: irq:31 memory:f7c00000-f7c3ffff ioport:e000(size=128)