Hi Andras
Linux Mint Olivia was released in July, so I assume it is based on
Ubuntu 13.04, which has codename Raring. However, I thought this
selection happens automatically. In a terminal you type:
sudo apt-add-repository ppa:gqrx/releases
sudo apt-get update
and it should automatically select the right version, import the
signature, etc. You should now see gqrx and GNU Radio packages in the
software manager or synaptic.
Note that the number after the codename is just a build counter for
the package and you do not put it anywhere
Alex