Question: I recently changed from Windows 10 to Ubuntu 18.04. I'm now facing a strange problem that I dont know how to deal with.

Downloading works perfectly until I start listening to some song on Spotify using Bluetooth headphones. When I click play, instantly my download rate goes to zero (or near it).

Here is the output of `lspci -knn | grep Net -A3; lsusb`:

```
03:00.0 Network controller [0280]: Qualcomm Atheros QCA9565 / AR9565 Wireless Network Adapter [168c:0036] (rev 01)
    Subsystem: Lite-On Communications Inc QCA9565 / AR9565 Wireless Network Adapter [11ad:0803]
    Kernel driver in use: ath9k
    Kernel modules: ath9k
04:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTL8411B PCI Express Card Reader [10ec:5287] (rev 01)
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 005: ID 04f2:b573 Chicony Electronics Co., Ltd 
Bus 001 Device 009: ID 04ca:3014 Lite-On Technology Corp. 
Bus 001 Device 003: ID 279e:024e  
Bus 001 Device 007: ID 04e8:6860 Samsung Electronics Co., Ltd Galaxy (MTP)
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

```

How to solve this slow connection issue?

Answer: 
The problem is with bluetooth and Wi-Fi working on the same radio frequency.

The coexistence technology is disabled by default for Atheros adapters, probably because long ago it could cause some problems for some old devices.

You can turn it on by running

```
sudo tee /etc/modprobe.d/ath9k.conf <<< "options ath9k btcoex_enable=1"

```

The setting will be applied after a reboot.

Just in case the setting can be reverted by

```
sudo rm /etc/modprobe.d/ath9k.conf

```
I'm running Ubuntu 18.04 on a Dell XPS.

My Wi-Fi was slow when using Bluetooth. I've added the following to `/etc/modprobe.d/iwlwifi.conf` and rebooted:

```
options iwlwifi bt_coex_active=0 power_save=0

```

Make sure you restart your computer afterwards.
It's been working fine for me since then.