MacBook Yosemite WiFI drops when other devices possibly interfere I am having serious WiFi issues on my MacBook Pro (retina Mid 2012 with Yosemite) where the connection continuously drops making Internet impossible to use. 

I have already tried all of the options described on various blog posts, including Fix Wi-Fi Problems in OS X Yosemite.

The problem is only happening on my MacBook Pro. While everything works fine on my MacBook Air, PC Win8 and two Android phones.

The router (UPC Ubee EVW3226) is set to:

2.4 GHz
802.11 bgn
WPA2/AES
Bandwidth 20 Mhz
Channel Auto
Beacon interval 100
DTIM int. 1
Fragment Threshold 2347


…and all other settings as recommended by Apple in Recommended settings for Wi-Fi routers and access points.

These are the devices I have:

MacBook Pro                  (WiFi drops all the time when laptop PC is on)
MacBook Air                  (works perfectly)
Lenovo Laptop with Windows 8 (works perfectly)
Android Phone 1              (works perfectly)
Android Phone 2              (works perfectly)


The problem actually only seems to happen when the Laptop PC is on, which makes me lead to believe it might be an issue with interference (though it's strange that it doesn't affect the MacBook Air (which is in the same room of the MacBook Pro).

I am getting really frustrated with all this and not sure what to try anymore.
Does anyone know if there is a solution apart from switching to Ethernet?
Analyse your wireless environment

A wireless interference problem is a lighting problem. It highly depends on the position of the different sources of radiofrequencies.
The core problem with this lighting problem is that we don't see within the multi-GHz bandwidth (hopefully).

Here is still today the best tool to analyze any wireless interference problem:

iStumbler

You should install it on a portable computer without any trouble to start with. From your environmnent description, I would install it on your MacBook Air.

Use it for many hours to get used to it and to your real wireless environment. Move with it within your work space. Use it at different hours: when all your equipments are running (don't forget the remote controls and the Blutooth equipments).

Control your wireless environment

Next, you show that your router is selecting the wireless channel on an
automatic way. This feature conceived to help beginners is one of the most harmfull function I ever saw in wireless environment.
This would have been a magic function within a fixed wireless environment. But this environmnet doesn't exist in real world.

Let me give you a practical example. Your neighbours are at work.
You start your WLAN router and finding the interfering neigbouring empty, this one choose (as most of this routers) the famous channel one.
Your neighbour come back from work, and their router was already automatically tuned on channel one. When they connect to their router this channel start to interfere with yours. Unfortunatelly, your router
isn't in the phase where it will change its preferred channel.

You stay on an everyday interfering wireless network.

Your neighbour(s) too :(.

Hence choose an empty channel and fix it. I advise you to avoid the channels 802.11b: 1-14 which are much slower and not necessary within your environment.