Thank you for your informative reply (and for taking the time to link that kext...).
Unfortunately, I couldnt get this to work. Here is what I did:
Downloaded Kext Beast to desktop and put the AirPortAtheros40.kext on the desktop with it.
Ran Kext Beast into /Library/Extensions
Launched Kext Utility to repair permissions
The only niggle that may have affected all of this is that restart does not seem to function correctly. I hit restart and the machine looks like its powering off for a reboot but screen stays black and nothing happens.
I therefore suspect it could be config.plist related?
I'm currently using Rehabmans custom config.plist for this generation of laptop (HP Probook 450 G1 with HD4600) as it was the only one that could get graphics working beyond 1024x768. I did however have to make a few tweaks to it to get it to play nice.
Could the restart not working be causing this? If so, how do I upload my config.plist for you to take a quick peek?
If you want me to have a look I will be happy to, right click on the config.plist file, select Compress.... and a zipped copy of the plist will be created, so you can attach it to a post here.
Laptops are notorious for creating issues, though the HP Probooks are the ones that people have got closest to working like an Apple MBP or MBA. There is a whole raft of information on hacking the HP Probook's over at Tonymacx86 and InsanelyMac. Rehabman has a lot of patches and fixes specific for the HP Probook family of laptops.
The first link is to a guide for HP Probook's installing El Capitan, oldish but definitely worth a read as it covers a lot of the basic issues that you will encounter.
Atheros WiFi Fix for Mojave. Atheros WiFi has been dropped from Mojave but there is a fix using the High Sierra Atheros40kext, attached below, and adding it to either Library/Extensions folder, or if that doesnʼt work then adding it to System/Library/Extensions folder.
Use KextBeast to install the kext, place the kext on your desktop for KextBeast to find it. KextBeast can be downloaded from Tonymacx86.
This fix may not work for all Atheros WiFi modules, you may need to check that the Vendor/Dev ID for your WiFi card is present in the kext. However, it has worked for common natively compatible Atheros modules that worked in previous macOS software versions.