I am using HP 15-ac173TU with a wireless chipcard from Realtek, rtl8723be. I was using Ubuntu 16.04 before and also encountered this problem and solved it using this answer.
Now when I have cleaned installed 18.04(due to some problems, I couldn't update from 16.04), it is blocking me when I try to run this command:
sudo add-apt-repository ppa:hanipouspilot/rtlwifi
which gives me the output as:
Err:8 http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu bionic Release 404 Not Found [IP: 126.96.36.199 80] Reading package lists... Done E: The repository 'http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu bionic Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.
I am guessing that Pilot6 hasn't issued any release for bionic of this driver, and so I am getting this 404 error. I have also tried using this command:
echo "options rtl8723be ant_sel=2" | sudo tee /etc/modprobe.d/rtl8723be.conf
and making a .conf file in the directory but still, it isn't helping me as the signal is very low.
I have installed Ubuntu in dual boot with Windows, although, when I am using Windows there isn't any problem as in Windows it chooses the antenna by itself.
I just want to know that is there any other way that I can rectify this problem and use my wireless without doing this. I have also seen this GitHub repository, but he clearly states that as I am using Ubuntu my APIs are modified. Hence, I couldn't use it.
I have researched and got this answer also, but it didn't make any sense doing it as I don't have any driver as mentioned in the answer.
I have done practically everything but still am getting this problem. Hope anyone in the community is kind to help me with this.