I am running Ubuntu 12.04 64bit dualbooting Windows 7.
My issue is with my D'Link DWA 140 RangeBooster N Adapter.

Apparently it uses the RaLink chip.

lsmod | grep ^rt 

gives:

rt2800usb              22684  0  

rt2800lib              58925  1 rt2800usb   

rt2x00usb              20762  1 rt2800usb   

rt2x00lib              55301  3 rt2800usb,rt2800lib,rt2x00usb   

My proper speeds should be actual download speeds of 2.0 MB/s ( ISP provides me with a 20Mbps connection). With this driver in Ubuntu, I barely get speeds of 50 KB/s.

Even then, it will momentarily disconnect at an estimated interval of 5 to 10 seconds everytime.

I have tried this guide to install the RaLink driver:

http://carlivar.tumblr.com/post/10230485625/fixing-rt2870-usb-wireless-in-ubuntu-or-debian

The problem with that guide was, with my first install of Ubuntu 12.04 I lost all Internet connectivity.
I am now on my second install of Ubuntu 12.04. I then tried this guide instead, I did every step:

http://www.cyberciti.biz/tips/linux-install-rt2870-chipset-based-usb-wireless-adapter.html

I managed to get through the whole thing without a problem, however upon doing:

lsmod | grep -i rt2870  

It returned blank. I had no internet connectivity and it did not recognize my D'Link adapter.

I have internet connection now because I removed the previous blacklist of those modules, disconnected and then reconnected the adapter to get it using the old driver.

A strange thing that confuses me is that, Ubuntu uses rt2800 while others recommend using rt2870 yet when I do this:

lsusb

I get this (truncated to show only relevant information):

Bus 001 Device 009: ID 07d1:3c0a D-Link System DWA-140 RangeBooster N Adapter(rev.B2) [Ralink RT3072]  

As you can see, it clearly says RT3072. I seriously have no clue what Ubuntu is or is not using in the background. I assume lsmod is telling me the truth. How can I fix this problem with my Internet connection? Its almost unusable. I wait for more than half an hour for it just to check if there are updates because the connection gets stuck in a state of temporary disconnection. It doesn't help that it cannot reach higher speeds than 50KB/s, and even thats rare.

This is not an issue with my adapter, as in Windows it works to its full potential. I have been having issues with this RaLink driver since 11.04. It's become so bad in 12.04 that I am pleading for help here.

Addendum

I have now also tried setting my wireless connection via Edit Connections. Under the Wireless tab, I edit my wireless and set IPv6 Settings to Ignore instead of Automatic as I have read elsewhere this also helps. In my case, this does NOT help.

I have also set my Wireless Power Management off via:

sudo iwconfig wlan0 power off  

This does switch off power management, but even this step does NOT help my connection from constantly speeding up one moment and dropping the next. I am getting really frustrated. I hope someone can guide me, or at least give me a tip that helped them previously regardless of hardware differences.