Your tar command looks fine.
If you are prefixed to the directory where the file was downloaded and the file was successfully downloaded what you are doing should work so I'm guessing that the download is ending prematurely or the ftp site is busy and you are getting an error response save as the output instead of the actual kernel source.
Look at the size of the file using: ls -l
and see if the file size is in the expected size range (47MB)
You can also try this: file <name of file>
which should yield this - bzip2 compressed data
I have had similar problems while downloading from kernel.org.
This is what I do:
right click on the link and select "copy link location"
open a bash shell and execute the following command:
wget -c <middle click - which should paste the url>
so the command looks like:
wget -c http://kernel.org/pub/linux/kernel/v...6.22.6.tar.bz2
This command should show you the download progress while it's downloading the file.
If the command dies just press up arrow (which should recall the last command) and execute the same command again.
The -c tells wget to continue so you won't have to start over.