The gqrx and MyriadRF PPAs are now updated to support Ubuntu 18.04 LTS. I tried to use as much as possible from the official repositories and only rebuild what was absolutely necessary:
All other packages are now provided by Ubuntu. This means we are making progress
New installation should work without problems, see for example the gqrx instructions.
If you upgrade, some of the packages may appear obsolete as they go from being provided by a PPA to being provided by Ubuntu. In such case uninstall the PPA version and let the package manager install the Ubuntu version. At the end it may be easier to reinstall the packages, e.g.
sudo apt-get purge --auto-remove gqrx sudo apt-get purge --auto-remove gqrx-sdr sudo apt-get purge --auto-remove libgnuradio*
and then, assuming you want gqrx:
sudo apt-get install gqrx-sdr